Edward Norman Maslen 1935-1997

Written by S.R. Hall and A.McL. Mathieson.

Ted Maslen's premature death on 2 February 1997, during a long distance run, shocked his many friends and colleagues around the world. A man of great energy and diverse talents, he made substantial contributions to the community and to sport as well as to Australian science.

Introduction

Prior to the Second World War, only a few scientists in Australia were involved in atomic structure studies using X-ray diffraction techniques. These were J. Shearer in the Physics Department of the University of Western Australia, D.P. Mellor in the Chemistry Department of the University of Sydney and, to a limited extent, J.S. Anderson in the Chemistry Department of the University of Melbourne. At the University of Adelaide, in the Physics Department, there were studies of electron scattering by R.S. Burdon.

During the War, the countries that normally supplied scientific equipment and materials to Australia were fully occupied with the provision of war needs. So, by necessity, Australian scientists had to devise means of production and that without delay. Thus, for example, an optical glass industry was created, optical devices manufactured, radar equipment constructed, and so on, as detailed in Mellor's volume of 'Australia in the War of 1939-1945' [1].

With the end of the War, the sense of confidence in the capability of science to solve problems and to contribute to post-war development encouraged the Federal government to support scientific research. One result was an effort to introduce advanced techniques by attracting scientists from overseas to contribute their knowledge and by arranging that young scientists in Australia proceed overseas to learn and then return to develop their new skills. As a result, nuclei of X-ray crystallography groups were created in Sydney, Melbourne, Adelaide and Perth.

In Perth specifically, C.J. Birkett Clews was appointed to the Chair of Physics of the University of Western Australia, having studied structure analysis by single-crystal X-ray diffraction at the Cavendish Laboratory in Cambridge. He initiated a number of students into the subject, one of whom was E.N. Maslen. After graduating BSc (Hons) in Physics in 1956, Maslen went to Oxford as a Rhodes Scholar.

In Oxford, he worked with Dorothy Crowfoot Hodgkin (Nobel Prize, Chemistry, 1964). His work there was mainly on the X-ray structure determination of certain antibiotic compounds but even in this biochemical area he gave evidence of an interest in the more physical aspects of crystallography. In 1960, he was awarded his DPhil. On his return to the University of Western Australia as a lecturer in the Physics Department, he proceeded to lay the foundations for what was to become a major school of crystallography, thus becoming a key figure in the development of this subject in Australia. He was a pioneer and later an established figure in the investigation of chemical bonding by precision studies of the electron density distribution in crystals. He contributed to many theoretical and experimental aspects of X-ray diffraction and explored basic questions in quantum chemistry. Latterly he utilized the great potential of synchrotron X-radiation in his studies. He was responsible for the formation of the Crystallography Centre at the University of Western Australia in 1972 and was its director until 1993 when he became head of the Physics Department.

As a recognized authority in the precision electron-density study of crystals, Ted was prominent in presenting the work of his group at international meetings. As a result, he became a important figure in the activities of the International Union of Crystallography (IUCr). In 1995, he was elected a Fellow of the Australian Academy of Science (AAS).

Background

Edward Norman Maslen was born at Kalgoorlie on 8 August 1935. His parents were William Michael Maslen, born on 1 October 1907 at Greenbushes, WA and Nellie Victoria Maslen (née Detez) born on 27 March 1905 at Merredin, WA. His father joined the Accounts Branch of the State Public Service in 1924 and, following correspondence courses in accountancy and part-time studies in English and Economics at the University of Western Australia, was attached to the Public Works Water Supply Department as an accountant. It is of interest to note that, at this time, he took up rowing with the Swan River Rowing Club. Because of changes associated with the Depression of 1929, he was transferred to Kalgoorlie. He completed his accountancy studies in 1933 and secured qualification with the Commonwealth Institute of Accountants with top marks for the State in Mercantile Law and Taxation. In 1934, he was admitted to the Chartered Institute of Secretaries with the second-highest marks in Australasia. In 1940, he became Officer-in-Charge of the Water Supply Department in Geraldton where Ted's schooling began at Saint Patrick's College (formerly Christian Brothers' College). His mother used to say that, even as a youngster, Ted always got into things and you didn't know what he would be up to next, indicative of his inquiring mind and superabundant energy. Ted was the second child and had an older brother, Victor, and a sister, Sue. All three became physicists, graduates of the University of Western Australia. In 1951, Ted won a General Exhibition and, in 1952, went to the University of Western Australia and St George's College to do a science degree. He was an outstanding student, gaining the Geology Prize in his first year and a Hackett Scholarship for 1955. He also became involved in student affairs, being elected in 1955 as President of the Guild of Undergraduates. 1956 was a momentous year for Ted. Apart from his role as President, he was very active in a student appeal to raise funds for a medical school within the University. For the latter, while competing in an athletic meeting, he inadvertently spiked himself and as a result contracted tetanus which was then a serious and often fatal disease. This was front-page news for several days and, even now, many people identify him as 'the student for whom traffic was diverted to keep his Royal Perth Hospital ward quiet'. This episode provided a very positive spin-off. The publicity was largely responsible for ensuring a generous subscription to the medical school fund and there is a photograph of a young, beaming Ted Maslen sitting up in a hospital bed handing over a cheque for £10,000 to the fund raisers. While all this was going on, Ted was a candidate for a Rhodes Scholarship, the announcement of which was withheld until he recovered. He was awarded the scholarship in 1956 and went to Oxford University at St John's College for the next three years. He completed his DPhil. studying molecular structure by X-ray diffraction techniques under the supervision of Dr Hodgkin. This was an inspirational period for Ted and was a dominant factor in his life-long interest in crystallography.

At Oxford, he met Sheila Robinson. Sheila's parents were Cyrus William Robinson, born on 29 October 1903, and Nora Teresa Robinson, born on 3 July 1905, both of Sunderland, England. Sheila and Ted were married in 1960, just before Ted took up a lectureship in the Physics Department of the University of Western Australia. They had three sons, Patrick, Daniel and Mark and five daughters, Barbara, Rebecca, Nicola, Catherine and Frances. The youngest of the boys, Mark, is following in his father's footsteps, having graduated from the University of Western Australia with First Class Honours in Physics. Several of the children, Patrick, Barbara and Nicola have followed Ted's interest and have degrees in Physical Education. Rebecca has degrees in Law and Commerce, Frances is an accountant, Catherine a physiotherapist and Daniel is studying viticulture.

This record of Ted's formative years reveals the personal characteristics of energy, enthusiasm, determination and personal involvement that in adult life were to manifest themselves in his dedication to his scientific research, his concern for his family, his students and, in the wider context, the University and the community.

Scientific contribution

During his forty years as a scientist, Ted Maslen contributed to almost every facet of crystallographic research. His main interest came to be precision electron density studies, but he was prepared to embark enthusiastically on allied projects ranging from the purely theoretical such as the solution of quantum mechanical systems, to the totally practical such as the design of collimators and diffraction instruments. Above all he was a determined individualist, confident enough in his abilities to 'go it alone' in a new field if expertise was not close at hand.

Structure elucidation

X-rays are scattered by electrons and the periodic scattering from atoms in crystals leads to interference, that is, diffraction. The electron density distribution of a crystal can be determined from measured X-ray diffraction intensities, provided the relative phase of each diffraction vector is derivable from other considerations. The determined distribution corresponds to the time-averaged integrated electron density of the atoms in the crystal and includes features due to bonding and vibrational modes. This approach leads to an atomic structure of the molecule or ionic entity in terms of a three-dimensional electron density distribution, thus defining its geometric parameters. Neutron diffraction provides similar structural information but in terms of atomic nuclei, so that a combination of X-ray and neutron diffraction can be useful and instructive.

Maslen's initial X-ray diffraction experience was the structural study of a pyrimidine (1), as part of his Physics honours thesis at the University of Western Australia. His doctorate from Oxford was for work on X-ray structure analyses of larger molecules of natural origin, the important antibiotics, cephalosporin C (2) and phenoxymethylpenicillin (3). Analysis of the latter allowed exploration of how sharpened Fourier coefficients improved structure determination (45).

On return to the University of Western Australia, Maslen followed two structural lines: one derived from his experience at Oxford on natural product molecules, while the other, associated with the structural properties of molecules with charged groups, zwitterions, focused mainly on aromatic molecules with amino and sulphonic acid groups. In addition, as appropriate to a physics department, his interest was in more general diffraction matters, particularly in measurement procedures that could improve the precision of structural studies. In time, this theme assumed dominance.

In respect of natural products, this was a period when X-ray diffraction became an important physical procedure capable of revealing the total structure of these relatively complex organic molecules, including their absolute configuration and details of conformation. By comparison with the more conventional methods of organic chemical analysis and synthesis, the diffraction approach provided unambiguous information about molecular structure, even though, at that time, it was a slow process because each diffraction intensity on film needed to be estimated by eye and the electron densities had to be calculated manually or with very slow computers. An additional obstacle was that suitable heavy-atom derivatives of the target compounds were required to assist in the phasing process, and these had to form suitable crystals. Nevertheless, organic chemists keenly sought the results of these analyses and Maslen determined the structures of a number of derivatives of natural products (5-10) using heavy atom and anomalous dispersion techniques. For methyl melaleucate iodoacetate (7, 7a), the anomalous scattering of CuKa radiation by an iodine atom was utilised to establish the phase angles of many reflections. This led to an estimation of the imaginary component, Df”, of the scattering factor for iodine (48).

Maslen determined other natural product structures (11, 12) using the so-called 'direct methods' phasing procedures based on the statistical structure-invariant relationships of Jerome Karle and Herbert Hauptman (Nobel Prize, Chemistry, 1985) which did not require a 'heavy' atom. In the second case, the normalized structure factors were not distributed evenly through diffraction space due to high anisotropic atomic displacement parameters and Maslen established a correction (18) (see 49,50) that led to an improvement in the modelling of the distribution, and hence to the solution of the structure by 'direct methods'.

Maslen's work on amino-benzene-sulphonic acids and amides (13-17) was aimed at studying the interaction between substituent groups attached to a benzene ring and a comparison of their hydrogen-bonding. In the case of ß-sulphanilamide (16), three-dimensional X-ray film data (a major measurement effort at that time) were used in conjunction with two-dimensional counter neutron diffraction data. Since the neutron data referred to nuclei, this provided improved information about bond length variations in the disubstituted benzene and in the related charged and neutral groups. His X-ray study of orthanilic acid revealed peaks of electron density above and below the plane of the benzene ring adjacent to the C – C bonds, indicative of p bonding contributions. This, and several other studies, highlighted for Maslen the opportunities for acquiring detailed information on chemical bonding from diffraction measurements.

During the 1960s he did other structural studies (19-25) to resolve specific chemical problems. However, as structure solution methodologies were better established, Maslen's focus shifted more to determining the fine detail of electron density distributions around and between atoms. With the creation of the Crystallography Centre at the University of Western Australia in 1972, structure analysis came under the general supervision of Dr A.H. White of the Chemistry Department. Even so, Maslen's interest in this aspect of crystallography continued throughout the 1970s, as is indicated in (26-43).

Electron density and bonding

Maslen's precision electron density studies, and particularly his use of the promolecule concept, were his most important and prolific contributions to crystallography. He became a recognised expert and respected authority in this field, though, not infrequently, his research directions and findings were somewhat controversial. As in most of his endeavours, Ted was a confident individualist who was undeterred by the consensus view or from offering unconventional interpretations, and this occasionally led to interesting editorial exchanges when the work was submitted for publication. His advice to colleagues on these occasions was 'one must always be prepared to educate referees'.

The electron density associated with bonding between atoms relates only to the outer electrons of the individual atoms, and therefore constitutes only a minor component of the total electron density distribution determined from a diffraction study. It is best observed by calculating the electron density difference distribution (or map), Dr = rexp – rcalc between the experimental electron density, rexp, derived from the X-ray diffraction data, and the corresponding distribution, rcalc, calculated from the co-ordinates and scattering capabilities of the non-bonded spherical atoms in the structural model as modified by their vibrational characteristics. Because these differences are usually small, the choice of modelling parameters that influence rcalc is a highly critical step.

Maslen's initial studies were on the bonding densities between carbon atoms. He recognised the importance of appropriate X-ray scattering curves in the resolution of Dr and applied the only theoretical curves available at the time, namely that by McWeeny [2] concerning bonded carbon. His examination (75) of the theoretical values of McWeeny in relation to graphite showed that, within the aromatic plane of the molecule, there is little deviation from isotropy. Prior to this treatment, the imaginary contribution to the scattering factor had been largely ignored and so he undertook to derive this for carbon in the case of diamond and graphite. These results showed the relation of this component to the antisymmetric distribution arising from s bonding in the case of diamond and the build-up between the carbon atoms, a result similar to that demonstrated by Dawson [3].

To determine the extent to which conventionally-measured diffraction data contained evidence of bonding, Maslen carried out a literature survey of electron density distributions (77). He observed that, for trigonally-bonded carbon, the aromatic C-C bonds contain a residual central peak of maximum ~0.2eA-3 with half height extensions about 0.3A in and 0.75A perpendicular to the trigonal plane. The most critical conclusion from this study was that the use of least squares to refine the structural model as isolated spherical atoms could obscure the detail of electron density variations associated with bonding.

This latter realization focused his attention on the possible use of aspherical scattering factors in the multipole refinement approach of Stewart [4], which he first applied to 1,3,5-triacetylbenzene (78). In an extensive survey (79) of multipole applications he concluded that the use of bond-directed scattering factors (78) was preferable and this led to five studies using this approach (80-84). The first was a neutron diffraction study of powdered diamond, the second a re-analysis of the available X-ray data on diamond, while the third investigated different electron density models for silicon using existing highly-accurate absolute measurements. The fourth paper, on s-triazine, was a more complex study while, in the final paper, he examined melamine using nuclear-centred multipole density functions in which the radial exponents were varied.

In an invited review of advances in precision density studies (85), Maslen summarized the field at the time. He pointed out that 'it now appears possible to observe directly the effects of forces on the density, which previously were merely inferred. As a consequence, charge density analyses are being used to improve our understanding of a wide range of physical and chemical concepts and phenomena, such as the degree of ionicity and the strength of covalent forces in chemical bonding, the nature of metal-metal bonds, hydrogen bonding, photochemical reactions, superconductivity transitions and Jahn-Teller distortions.'

His review also foreshadowed a change in interest from the lighter elements and mono-atomic crystals to compounds containing heavier metals and longer-range interactions. This was at a time when heavy-atom structures were generally considered as unsuitable for precision analysis. In the study of several transition metal complexes (86, 87) he gave close attention to the region adjacent to the metal atom. In the redetermination (88) of the classical structure, copper sulphate pentahydrate, dominant density differences near two crystallographically-independent Cu atoms were related to the re-distribution of the Cu 3d electrons associated with bonding. He claimed that the polarized density resulted from second-nearest-neighbour interactions and that these were significant and important to bonding.

From this point on, Maslen showed a preference for studying families of compounds in which the structure remained unchanged except for the central metal atom. This enabled modifications in Dr distributions to be interpreted in terms of changes in the orbital distribution of the central metal atoms. In the study of Tutton's salts, (NH4)2M(SO4)2.-6(H2O)6, an isomorphous series with a divalent metal, M = Mg, Ni, Zn or Cu (95-99) by X-ray and neutron diffraction methods, Maslen observed that the Dr distributions near the metal atoms were similar except for differences arising from the d-electrons. An extensive examination followed of the nona-aqualanthanoid(III) tris(trifluoromethanesulphonates), [Ln(H2O)9](CF3SO 3)3 complexes with Ln = La through to Lu, which form an isomorphous series of hexagonal structures (100, 101), and these presented an intriguing series of closely-related electron density maps.

Maslen's earlier density studies had involved predominantly 'neutral' atoms. This was because the partitioning of the electron density distribution is more difficult when atomic charges are involved and the Hirshfeld partitioning approach preferred by Maslen had to be applied judiciously. For example, the charges he determined for a series of transition metal perovskites, KMF3, M = Mn, Fe, Co, Ni, and Zn (102-105) changed monotonically through the series but the polarization near Zn is significantly aspherical and the Zn, K and F atomic charges were +0.18, +0.47 and – 0.21e, respectively. That is, the determined polarity is consistent with conventional charges, but the magnitudes are less than the formal values (see also 121).

A study of the copper perovskite KCuF3 (105) by Maslen guided the analysis of the more-difficult-to-crystallize superconducting compound YBa2Cu3O7-x (106) in relation to determining a position-space model for the superconducting behaviour. It is evident from this and later studies (for example 126, 128, 133) that his views had moved away from the conventional wisdom of anion-anion interactions dominating the distribution of the electron density, to holding that the cation-cation interactions were more significant.

At about this juncture, Maslen's group became more concerned with the effect of extinction on their measurements of intensity. Extinction is an important universal effect in the measurement of intensities from even small single crystals and is due to multiple interference within the crystal. Correction for this effect is generally based on theoretical mathematical models derived originally by Darwin [5] and elaborated by Zachariasen [6] and others, which Maslen had used in his earlier Dr studies. However, in a careful analysis of data in relation to a-Al2O3 (67), Maslen revealed that the param
eters derived from this procedure were physically unrealistic, the corrections being rather sensitive to the weighting of the observations of the intense low-angle reflections. He devised an alternative procedure for the assessment of extinction, more closely allied to experiment. In this, corrections for extinction are evaluated in respect of equivalent reflections with different path lengths through the crystal (68, also 71-73). (Such 'corrected' intensities for equivalent reflections should, in principle, be equal.) Corrections by this procedure tended to be smaller than those based on minimizing the difference between Fobs and Fcalc. The reliability of this procedure is, however, dependent on knowing the crystal shape accurately, the crystal being asymmetric, and on precisely measured intensities for symmetry-equivalent diffraction data (that is, the method is optimal for high-symmetry space groups).

From this time on, Maslen placed increasing reliance on the use of synchrotron radiation at the Photon Factory at Tsukuba in Japan, especially using off-focus beams to ensure better beam uniformity. The much greater beam intensity and monochromaticity greatly improved the signal/noise ratio of the measurements and this was important because he and his colleagues were early users of 'microcrystals' (that is, crystals less than 1000 microns3 in volume) to minimize extinction effects. This reduced the effect of random errors in the measurements and substantially enhanced definition of the density distributions. These improvements in precision provided the basis for an investigation of optical, electrostatic and magnetic properties attributable to aspherical electron density. Maslen's study of rhombohedral carbonates with Ca, Mg, and Mn (115-120) showed a correlation of the Dr distributions with physical properties of optical anisotropy. Lattice mode frequencies predicted from eigenvalues of the T and L tensors for the CO3 rigid group motion in these structures were close to spectroscopic values. The Dr topography near the CO3 groups showed the influence of the cations and correlated strongly with the refractive indices.

Maslen's interest in heavy-atom bonding extended across much of the periodic table, and included the rare-earth elements. Typical synchrotron studies were the rare earth oxides (139, 140) and the perovskite-type orthoferrites (133-5) in which strong magnetic interactions between heavy-metal atoms gave rise to pronounced bonding effects that were readily studied by r methods.

Maslen's use of the modelling factors that determined electron density distributions evolved considerably over his career. However, underpinning much of these efforts was the consistent application of the Hirshfield approach to partitioning electron density in relation to the individual atoms. The reasons for this are discussed in the next section. Definitive articles on X-ray scattering (64) and X-ray absorption (65) were contributed by Maslen to the International Tables for Crystallography.

The promolecule

The choice of the non-interacting spherical ground-state atomic model for the calculation of rcalc is critical to the interpretation of the measured electron density distribution, and is referred to as the 'promolecule' or independent atom model (IAM). The method of partitioning the electron density distribution, so as to allocate the proper charge component to the individual atom, has an important bearing on the efficacy of this approach in the study of chemical bonding.

Maslen carefully scrutinized the two available schemes for partioning, those of Bader and of Hirshfeld, using theoretical wavefunctions for forty heteronuclear diatomic molecules (141). The atomic charges derived by these procedures were compared closely with electronegativity differences and with dipole moments. The Hirshfeld procedure, in which component electron distributions are overlapping and continuous, was preferred and applied thereafter by Maslen and his colleagues in estimating atomic charges from X-ray diffraction data.

He illustrated the importance of the promolecule approach in determining chemical properties from electron densities with the study of atomic radii, atomic charges derived from partitioning and electrostatic energies (142). These results were compared with the corresponding quantities from theoretical and experimental studies of a large number of diatomic molecules. He pointed out that the promolecule intrinsically contains useful chemical information, the effect of which on the Dr distribution is sometimes mistakenly attributed to chemical bonding.

Subsequently, Maslen showed that the differences between experimental and accurate Hartree-Fock binding energies are strongly correlated with the classical
electrostatic interaction between spherical atoms for a large number of diatomic and polyatomic molecules (143). These results led to an estimate for the molecular extra correlation energy. He extended this approach (144) to test the IAM model with calculations of cohesive energies that compared favourably with the Madelung energies for a wide range of solids. IAM energies provide better estimates for the alkali halide lattices than do the Madelung energies.

In respect of atom size and charge in the alkali halides LiF, NaF and LiCl (145), Maslen claimed that the lowering of the potential energy, due to overlap of atomic electron densities, is an accurate approximation to the bonding energy.

Maslen also applied the IAM approach to the 3d transition metals (146), a class of solids the cohesive energy of which is not approximated by the classical electrostatic overlap energy due to the near-degenerate nature of the ground states. He showed that if the 3d metals were regarded as being in prepared states prior to bonding, the bonded electrostatic energies are better approximations to the observed binding energies.

Maslen's study of diatomic molecules led to a re-appraisal (147) of Berlin's theorem [7]. It had been observed experimentally that the central build-up of difference electron density typical of carbon-carbon bonds did not occur in the case of bonds N–O, O–O, Cl–Cl, and so on. Berlin's theorem underpinned the common assumption that an increase in the electron density at the mid-point of a covalent bond is essential to the stability of the bonded nuclei. While Berlin's theorem focused on the total electron density, which must be positive everywhere, the difference between the experimental density and the spherical model density may be positive or negative. In studies of theoretical electron densities for N2 and F2, Maslen observed that the only substantial contribution to the overall binding appeared to come from regions along the internuclear axis and close to the nuclei. According to this interpretation, the build-up of density near the mid-point of the bond plays almost no role in binding the nuclei and is not a necessary condition for binding.

Somewhat later, in his final publications in this area (148-152), Maslen stated that it was physically reasonable to subdivide the total electron density of the promolecule in proportion to each atom's contribution to the electrostatic potential. He assessed atomic charges as the differences between atomic numbers and the integrals of partitioned electron densities. Promolecular charges evaluated for 160 lattice-compounds indicated that cations acquire control over the electron distribution at the expense of the anions. He attempted to show a consistent relationship between the ground state electron configurations and the atomic radii in which the invariant component of the radius associated with the atomic cores can be equated with the value at which the integral of the density equals the number of the core electrons. The tests made on diatomic molecules were promising and would presumably have been pursued further had it not been for Maslen's untimely death.

Theoretical chemistry

During the 1980s, part of Maslen's research activity, and that of his students, was directed towards the application of the emerging symbolic computing methodologies. His use of algebraic packages, such as Mathematica and REDUCE, to tackle quite daunting quantum mechanical problems, was a tribute to his remarkable scientific versatility.

Maslen's papers (153-157) marked the first phase of a very determined attempt to find an exact closed-form expression for at least the ground-state wave function of helium. Though not successful in this, his work did lead to the discovery of a closed form for a second-order term in the expansion of that wave function, that had eluded previous attempts by others over a long period. Maslen's introductory paper opened by challenging the pessimistic view of the possibility of finding exact solutions for three – and four-body systems and series methods were applied in conjunction with a spherical polar co-ordinate system to the problem. However, simple exact expressions could only be obtained for early members of the series: even if this hurdle could be overcome, there still remained an infinite number of arbitrary coefficients to be determined. Maslen showed that this number could be reduced dramatically by taking account of the expected asymptotic behaviour of the wave function. The summary paper reflected on the question 'can an exact solution be obtained' and it concluded that this could be done if, in some representation, only a finite number of the arbitrary coefficients were non-zero. This set of papers greatly clarified the problems involved in seeking an exact wave function for helium.

Maslen followed with five exploratory papers (158-162) which, in addition to other useful results, threw light on the mathematical form of the exact wave function for helium and studied the relative merits of several sets of co-ordinates.

His next three papers (163-165) represent a second attempt to obtain the exact wave function for helium and great use is made of computer algebra to handle the heavy mathematical calculations. The first of these papers included an echo of his earlier comment in stating that the outlook for simple closed-form helium wavefunctions is more favourable than is generally believed. In (164), use is made of spherical polar co-ordinates to achieve full reduction of the second-order term to a closed form. However it was clear that the task of extending this achievement to higher-order terms would be immense. Paper (166) presents some useful reduction formulae for generalized hypergeometric functions of one variable while (167) derives a compact analytical formula for two-electron two-centre integrals over Slater functions. This work of Maslen and his co-workers has been recognized by Myers et al [8] as 'impressive both in its accomplishments and its innovative use of symbolic algebra'.

Primary research goal

While much of Ted Maslen's research was directed at understanding and resolving specific problems, a consistent goal throughout his career was the development of a unified view of chemical bonding. Probably the most succinct insights into what he saw as his 'holy grail' are contained within an eight-page document entitled A Unified View of Chemical Bonding, prepared in 1993 for internal circulation to his research students.

In this he states that to understand chemical bonding, precise knowledge is needed of the properties of atoms relevant to the interaction that brings them together. He observed that the topographies of the experimentally-determined aspherical densities are usually consistent with the view that the valence electrons that overlap with the cores of their neighbours are transferred by exchange repulsion to the interatomic regions of low electrostatic potential. However, he also stated his belief that regions remote from the atomic sites would reveal density information important to understanding physical and chemical phenomena. Thus from an initial concern with the density distribution between individual atoms, a more diversified view related to the distribution of cations is evident. Although his early death prevented a full development of this approach, his indelible legacy to the field of high-quality measurements and their perceptive evaluation has undoubtedly contributed significantly to the ultimate understanding of the chemical bond in terms of electron density distributions.

Contributions to academia

On his return to Australia from Oxford in 1960, Maslen began, with characteristic vigour, to activate the crystallography group. Though he expected of his students no less than he demanded of himself – the highest possible academic standards – his genuine concern for their progress and welfare meant that postgraduates were quickly attracted to his group. Over the years he supervized more than forty MSc and PhD students.

At Oxford, Maslen had been one of the early crystallographers to use electronic computers for structure determination. When he returned to Perth there was only one computer in Australia, SILLIAC, at the University of Sydney and Maslen made use of the facilities provided at that machine by Dr H.C. Freeman's group of crystallographers there. Although access to SILLIAC was a vast improvement over the use of calculators, a cycle of computing could still take the Perth group several weeks, and a local computer was clearly desirable. Maslen successfully campaigned, with Dr R. Dingle of the Physics Department and Dr J. Ross of the Psychology Department, for the purchase of a computer, and in 1962 an IBM 1620 was installed. Throughout the 1960s, crystallographers were the major users of the computing facility, both at the University of Western Australia and at most other university computing centres around the world. Maslen was a member of the University's Computer Coordinating Committee for many years and encouraged the University to take an important step in purchasing one of the world's first commercial time-sharing digital computers, a DEC PDP6, which was delivered in 1966. An attempt to control a Hilger and Watts four-circle diffractometer with the PDP6 was unsuccessful, but provided useful training for some students in real-time computing and machine control. Maslen soon recognised the potential of the minicomputer and
microcomputer as cost-effective computing options for crystallographers and physicists, and in the mid-1970s he argued vigorously that mainframe computers were no longer economical for universities.

During the period 1970-80, Maslen contributed much to university administration. In 1970, he became Chair of the University of Western Australia's Physical Sciences Research Grants Sub-committee. The 1970 Cole Report to the University Senate recommended that large-scale instrumentation be shared between departments. The combined efforts of Maslen and A.H. White of the Chemistry Department led to the establishment in 1972 of the Crystallography Centre with Maslen as director and White as deputy director. He held many other administrative posts, being an elected member of Professorial Board 1972-78 and 1984-86, a member of the University Research Committee 1973-78, of the Radiation Safety Committee from 1974 (Chair from 1977), and a member of the St George's College Council, 1978-87.

In addition, there were extra-curricular commitments: as a member of the Cancer Council (Western Australia) 1971-81, of the Radiological Council (Western Australia) 1974-85, and of the CSIRO State Committee for Western Australia 1976-80. He was a member of the Western Australian Rhodes Scholarship Selection Committee 1970-75 and was secretary from 1978. Indifferent to the conventional trappings of ceremony, Maslen would arrive at the annual selection meeting, held at Government House under the chairmanship of the Governor, on his battered bike with his well-worn green case containing the papers and reports. While he had no direct say in the choice of the Scholar, he was an adept secretary, bringing an item of relevant information to the committee's attention at the crucial moment.

With some reluctance, Maslen became Head of the Physics Department in 1993. The department, like others in Australia, faced problems with decreasing student numbers and reduced budgets. Maslen played a leading role in developing biophysics courses at the University and it is arguable whether, without his leadership, this programme, which has grown from a handful of second-year students in 1995 to representation at all levels, would have happened at all.

The position of Physics Head in the mid-1990s was not easy. Redundancies were necessary. Almost without exception, however, his colleagues considered Maslen to be the right man at the helm for the times. His dealings with university administrators were not always so well received. In the first place, Maslen was very direct or, as a senior colleague put it, 'for him diplomacy was just another term for telling lies'. This is not to say that he was intentionally rude or abrasive but he was scrupulously honest and curried no favours, at any level. Ted was tenaciously outspoken and even passionate, both in committee and in correspondence. On campus and elsewhere, he was viewed as a valuable ally and a formidable foe.

In a letter in which Maslen expressed his concerns about current university decision-making, he wrote: 'Traditional academic protocols are a distillation of the collective wisdom over generations. Those protocols have never become tiresome restrictions on brilliant minds, but, on occasions, have held in check the mediocre and the hare-brained.'

Contributions to the profession

In 1974, Ted was Chairman of Topic 1, 'Real Atoms in Crystals', of the International Conference on 'Real Atoms and Real Crystals' that was sponsored by the International Union of Crystallography (IUCr) and the Australian Academy of Science (AAS) and held in Melbourne. He was Vice-President of the Society of Crystallographers in Australia (SCA) 1978-79 and its President 1980-81. He was a member of the IUCr Commission on Charge, Spin and Momentum Density 1975-81 and was elected to the IUCr Executive in 1984. For the 1987 Triennial Congress, Perth was selected as the conference venue and Ted appointed Chair of the Organising Committee. In order to contain costs, the Crystallography Centre eschewed professional support to deal with organizational details. In the event, there was a significant profit, the SCA, which underwrote the conference, being the beneficiary. This outcome arose for two reasons: attendance was greater than had been originally planned for, and the registration fees were in US dollars and there was a fortuitous shift in exchange rates during the conference. The resultant income is now used to help students attend crystallographic conferences. In 1997, in recognition of Ted's
efforts in respect of the Congress, these funds were called the 'E.N. (Ted) Maslen 1987 Studentships and Scholarships'.

Maslen's membership of the IUCr Executive ended in 1990 but, because he was a strong advocate of electronic publishing for IUCr journals, he was appointed to the post of IUCr Director of Archiving and Crystallographic Information 1990-1993. Prior to that he had chaired a working party on crystallographic information (1987-1990). This eventually resulted in the development of the Crystallographic Information File [9] that was adopted by the IUCr for data exchange and is now used widely in the structural sciences for journals and databases. He later became the Chairman of the IUCr Committee on Electronic Publishing, Dissemination and Storage of Information 1993-96.

Maslen also made a foundational contribution to the Australian Institute of Nuclear Science and Engineering (AINSE) neutron-scattering group set up in the late 1950s as an interface between the Atomic Energy Commission and the universities. He was one of the first neutron scattering users at Lucas Heights and his group established an excellent collaborative presence at that facility. In the early years of the group, he would drive across the Nullarbor to AINSE with a car-load of research students. The driving was shared so that continuous progress could be made, and at change-over time the fresh driver would be required to fill the tank before getting behind the wheel. It then became a competition to see who could drive the car furthest on a single tankful of petrol. These cross-country expeditions on the then-unsurfaced Nullarbor 'highway' were part of student folklore. On one occasion Maslen managed to obtain some cheap accommodation for himself and his students in Sydney, only to find that no-one could sleep because of the incessant foot traffic outside their rooms in this particular Kings Cross Hotel. He complained to an incredulous hotel management but was given a refund.

On the sporting field

For his whole life, Ted was an intensely keen and competitive sportsman, especially in rowing and athletics. He is often remembered for his sporting achievements as a student. Although the University Athletic Club had been long established, there were just six members when Ted joined in 1952.

With him, there were no half-measures. For the next three summer vacations, he worked as a weighbridge clerk on the wheat bins some hundreds of kilometres from Perth but did not miss a Saturday afternoon competition at suburban Leederville Oval, travelling the long distance on his motor cycle. He was elected Captain of the Club in 1955. He also took up rowing at the University of Western Australia, joining the university boat club in 1952 and becoming club Captain in 1954.

At Oxford, he enthusiastically took to both academic work and sporting endeavour. One morning, he and a friend went by train to London, changed into running gear and ran non-stop from Marble Arch back to St John's – some sixty miles. His rowing prowess was honed at Oxford. His Isis eight took the Head of the River in 1957 and was the reserve crew for that year's annual Oxford-Cambridge clash. He was successful also in double sculling events. The trophy oars, suitably inscribed, hang proudly in the Maslen home. Ted acquired an Oxford half-blue.

In Perth, to ensure time for exercise, he carefully controlled how his time was allocated. As the family increased, Sheila had greater need of the car and Ted started to ride his bicycle to university. He rose at 5:30am, attended early morning mass and made breakfast and lunch sandwiches for the family, and then rode his bike some fifteen kilometres to the University of Western Australia campus. At the university, his end-of-day regime included an hour's run, often in the company of students and other staff, and then home by bike.

In spite of a tendency for his shoulder to dislocate, he liked to play cricket and football. On one such occasion when playing football at Oxford, his shoulder dislocated and he quietly asked a colleague in the other team if he would mind pulling on the arm to get it back into the socket. Ted played on but his colleague's concentration never quite recovered and Ted's team won easily.

In Western Australia, Ted stroked the senior eight from 1960 to 1970. University had not won a State eight's championship in eight years, then in 1963 Ted stroked a novice crew to victory. He subsequently rowed for Western Australia in the Kings Cup. In 1964, having stroked the University eight, the coxless four and the coxed four and been undefeated for the whole season, Ted was named Oarsman of the Year.

He was President of the University Athletic Club from 1960 to 1962. The club went on to become the State's most successful, and he remained a member for forty-five years. He was the ultimate 'club man'. He would run, walk, hurdle, jump, pole vault, to help his team score points and to encourage others. Ted is most fondly remembered for his Herculean efforts in the steeplechase. This event was always run on the hottest part of the day and Ted was always there – without a hat, and barefoot on a scorching track – trying to win or get a place, but above all to run a personal best time and score points for his club. He always gave 110% and invariably finished in a state of exhaustion, from which he quickly recovered to compete in the 5,000 metres a little later in the day, again to finish in a state of exhaustion but pleased with a good day's distance running.

In 1977 at the Australian Veterans' Championships Ted raced against Albie Thomas, Olympian and former world record holder for the mile. In a fast and hard-fought race Ted came to the line a second in front of that great Olympian in 4 minutes 15 seconds – an Australian veteran record for the mile. That was the highlight of his athletic career, he said. The Western Australian State steeplechase records for the veteran classes, M35, M40, M45, M50 and M60 were all held by Ted.

Service to the community

Ted gave outstanding service to the South Perth City Council, serving as a councillor for thirteen years between 1976 and 1995 as an independent. He not only kept an eye on the big planning picture but was conversant with detail at a local level to ensure maintenance of lifestyles and quality of life. He was one of the earliest to protest, on behalf of the inner Perth municipalities, at the mounting traffic volumes being disgorged into the city each day. He thus became an early advocate of ensuring that these traffic volumes were kept off suburban streets not designed for the high-density traffic, but directed to streets that were.

He was an ideal councillor in at least one important respect. In a State where party politics exists, but not overtly, in local government, Ted was genuinely of an independent mind and spirit. His personal politics remained his private affair. He believed strongly that solutions to problems lay in better information, planning and action. He often surprised authorities by his knowledge in their area of expertise and, on detailed investigation, he was more often than not successful with his proposed solution. In such cases, he was always fair, always direct, but uncompromising in getting at the truth.

Party politics aside, Ted in the local council did not 'politic' in the personal or factional sense. Again, as would appear consistent with his general intellectual rigor, he took the view that logic and merit would, or at least should, be the deciding factors. Thus he did not need to resort to the histrionics that might fall to others in public life. There was also an element of what was proper and what was improper in one's conduct. He obviously felt that, at a political and a personal level, the task could be done without the bitterness or division that so often passes as public debate in Australia.

A memorial tribute

A memorial evening was held to honour Ted on 2 June 1997 in Winthrop Hall at the University of Western Australia. This evening, only the third such occasion in the history of the University, reflected the esteem in which he was held as an undergraduate, a Guild President, a Rhodes Scholar and a member of the Physics Department for 37 years. It brought together his many friends and colleagues from academia, science, sport and the community. Among the many tributes paid to Ted on this evening, some of which have been included in this record, the most poignant were those made on behalf of his ex-students by Roger Price. Ted saw his responsibility for his many students, and their careers, as being more important than his own academic advancement. It was this selfless dedication to the discipline and to science that makes it fitting to close this record with a selection of his student's reminsciences:

'He let people be themselves, and did not push his students, but whenever you showed enthusiasm for a project, Ted matched it many times over.'

'Ted gave the uncanny impression that you were the sole focus of his time and energy.'

'At 5 in the morning at the Photon factory in Japan, Ted and I finally found the reflection we had been looking for after several days with little sleep and over 18 hours without a break...then my experiment began in earnest. I have Ted to thank for these data which formed the basis of my PhD. Anyone less concerned for my welfare as a student would have given up.'

'One of the reasons why Ted was held in such high regard by the young of his discipline was that he understood that doing good, coal-face science is hard work. Pursuit of scientific knowledge at the frontier is as difficult as any human endeavour that you can name. And invitations for physicists to endorse a breakfast cereal are few and far between. It tests mental endurance, inventiveness, and often lays siege to self-esteem. It demands a willingness to destroy one's most cherished intellectual edifices when the evidence is unassailable.'

'As a student at the threshold of the great intellectual journey, you need a mentor, a friend, and an expert guide through the thicket (and sometimes the minefield) of existing publications, half-formed ideas, blind alleys and conjectures on which you must base your own research. Ted was all of these.'

'He was "one of us" – whether it was when he shed his shoes but otherwise remained fully clothed for a cricket match, when he bounded out of the Physics Department every afternoon at 5 o'clock wearing a raggy singlet for a run through Kings Park accompanied by that day's fellow joggers, or when he expressed frank delight in a student's solution of a complex algebraic problem – the kind of delight reminiscent of the best moments of wonderment in one's early career as a student.'

'Ted was an eccentric, in the sense that the term is used to describe those charismatic, unconventional and fulfilled individuals who greatly enrich our lives.'

About this memoir

This memoir was originally published in Historical Records of Australian Science, vol.13, no.3, 2001. It was written by:

  • S.R. Hall, Crystallography Centre, University of Western Australia.
  • A.McL. Mathieson, Chemistry Department, La Trobe University, Victoria.

Numbers in brackets refer to the bibliography; numbers in square brackets refer to the references.

Acknowledgments

We thank Dr Victor W. Maslen, brother of Ted, for providing details relating to family matters and for preparing the summary of material for the section on theoretical chemistry. Thanks are also due to Ted's collaborators, Mark Spackman and Victor Streltsov, for their help with the precision density and promolecule sections, and to Allan White for his contributions. We are grateful for permission to use items from the memorial service at the University of Western Australia contributed by David Carr, Cyril Edwards, Michael McCall, Bernard Moulden, Phillip Pendal and Roger Price.

References

  1. Mellor, D.P. The Role of Science and Industry. Series 4, Vol. 5 of 'Australia in the War of 1939-1945', Canberra: Australian War Memorial.
  2. McWeeny, R. X-ray scattering by aggregates of bonded atoms IV. Applications to the carbon atom. Acta Cryst. 7, 180-186 (1954).
  3. Dawson, B. Aspherical atomic scattering factors for some light atoms in sp3, sp2 and sp hybrid valence state approximations. Acta Cryst. 17, 997-1009 (1964).
  4. (a) Stewart, R.F. Generalized X-ray scattering factors. J. Chem. Phys. 51, 4569-4577 (1969). (b) Stewart, R. F. Valence structure from X-ray diffraction data: an L-shell projection method. J. Chem. Phys. 53, 205-213 (1970).
  5. Darwin, C.G. The reflection of X-rays from imperfect crystals. Phil. Mag. 43, 800-829 (1922).
  6. Zachariasen, W.H. A general theory of X-ray diffraction in crystals. Acta Cryst. 23, 558-564 (1967).
  7. Berlin, T. Binding regions in diatomic molecules. J. Chem. Phys. 19, 208-213 (1951).
  8. Myers, C.R., Umrigar, C.J., Sethna, J.P. and Morgan III, J.D. Fock's expansion, Kato's cusp condition and the exponential ansatz. Phys. Rev. A44, 5537-5546 (1991).
  9. Hall, S.R., Allen, F.H., and Brown, I.D. IUCr Commission on Crystallographic Data, Commission on Journals, Working Party on Crystallographic Information. The Crystallographic Information File (CIF): A New Standard Archive File for Crystallography. Acta Cryst. A47, 655-685 (1991).

Bibliography

Structure analysis

  1. Maslen, E.N., Jukes, D.E. and Clews, C.J.B. The crystal and molecular structure of 2:5 diamino-4-mercapto-6-methyl pyrimidine. Acta Cryst. 11, 115-121 (1958).
  2. Hodgkin, D.C. and Maslen, E.N. The X-ray analysis of the structure of cephalosporin C. Biochem. J. 79, 393-402 (1961).
  3. Abrahamsson, S., Hodgkin, D.C. and Maslen, E. N. The crystal structure of phenoxymethylpenicillin. Biochem. J. 86, 514-535 (1963).
  4. Clews, C.J.B., Maslen, E.N., Rietveld, H.M. and Sabine, T.M. A neutron diffraction examination of p-diphenylbenzene. Nature 192, 154-155 (1961).
  5. Maslen, E.N., Nockolds, C.N. and Paton, M.G. The stereochemistry of lirioresinol-B. Aust. J. Chem. 15, 161-162 (1962).
  6. Duffield, A.M., Jefferies, P.M., Maslen, E.N. and Rae, A.I.M. The structure of bruceol. Tetrahedron 19, 593-607 (1963).
  7. Hall, S.R. and Maslen, E.N. The determination of the crystal structure of methyl melaleucate iodoacetate. Acta Cryst. 18, 265-279 (1965).
    7a. Chopra, C.S., Fuller, M. W., Thieberg, K.J.L., Shaw, D.C., White, D.E., Hall, S.R. and Maslen, E.N. Triterpenoid compounds: VI Constitution of melaleucic acid 2. Tetrahedron Letters, 1847-1852 (1963).
  8. Oh, Y.-L. and Maslen, E.N. The crystal and molecular structure of davallol iodoacetate. Acta Cryst. 20, 852-864 (1966).
  9. O'Connell, A.M. and Maslen, E.N. The crystal structure of beyerol monoethylidene iodoacetate. Acta Cryst. 21, 744-754 (1966).
  10. Paton, M.G. and Maslen, E.M. The crystal structure of dibromoeriostoic acid. Acta Cryst. 22, 120-133 (1967).
  11. Oh, Y-L. and Maslen, E.N. The crystal and molecular structure of isoeremolactone. Acta Cryst. B24, 883-897 (1968).
    11a. Oh, Y-L. and Maslen, E.N. The structure and stereochemistry of isoeremolactone. Tetrahedron Letters, 3291-3294 (1966).
  12. Huber, C.P., Hall, S.R. and Maslen, E.N. The crystal structure of oxotuberostemmonine. Tetrahedron Letters, 4081-4084 (1968).
  13. Rae, A.I.M., and Maslen, E.N. The crystal structure of sulphanilic acid monohydrate. Acta Cryst. 15, 1285-1291 (1962).
  14. Hall, S.R. and Maslen, E.N. The crystal structure of metanilic acid. Acta Cryst. 18, 301-306 (1965).
  15. O'Connor, B.H. and Maslen, E.N. The crystal structure of a-sulphanilamide. Acta Cryst. 18, 363-366 (1965).
  16. O'Connell, A.M. and Maslen, E.N. The crystal structure of b-sulphanilamide. Acta Cryst. 22, 134-145 (1967).
  17. Hall, S.R. and Maslen, E.N. The crystal structure of orthanilic acid. Acta Cryst. 22, 216-228 (1967).
  18. Maslen, E.N. A method for allowing for thermal anisotropy in evaluating Wilson plots and normalised structure factors. Acta Cryst. 22, 945-946 (1967).
  19. Rietveld, H.M. and Maslen, E.N. The crystal structure of cadmium n-butyl xanthate. Acta Cryst. 18, 429-436 (1965).
  20. Paton, M.G. and Maslen, E.N. A refinement of the crystal structure of yttria. Acta Cryst. 19, 307-310 (1965).
  21. O'Connor, B.H. and Maslen, E.N. The crystal structure of Cu(II) succinate dihydrate. Acta Cryst. 20, 824-835 (1966).
  22. O'Connor, B.H. and Maslen, E.N. A second analysis of the crystal structure of copper (II) diethyldithiocarbamate. Acta Cryst. 21, 828-830 (1966).
  23. Jones, R.O. and Maslen, E.N. The crystal structure of the p-complex [C6H4(CO)2 ]2. Z. Krist. 123, 330-337 (1966).
  24. Rae, A.I.M. and Maslen, E.N. An X-ray diffraction study of nickel cyanide ammoniate. Z. Krist. 123, 391-396 (1966).
  25. Robinson, D.J., Kennard, C.H.L., Maslen, E.N. and Temple, D.M. Crystal structure of [1,1,4,4,-tetraethylpiperazinium] dichloride-4-(p-nitroaniline). J. Chem. Soc. B, 1317-1322 (1970).
  26. Dewan, J.C., Kepert, D.L., Raston, C.L., Taylor, D., White, A.H. and Maslen, E.N. Crystal structures of tris(NN-diethyldithiocarbamato)oxo-niobium(V) and – vanadium (V). J. Chem. Soc. (Dalton), 2082 – 2086 (1973).
  27. Brotherton, P.D., Maslen, E.N., Pryce, M.W. and White, A.H. Crystal structure of collinsite. Aust. J. Chem. 27, 653-656 (1974).
  28. Maslen, E.N., Engelhardt, L.M. and White, A.H. X-ray crystal structure of {7,8,15,17, 18,20-hexahydrodibenzole[e,m]pyrazino-[2,3-b][1,4,8,11]tetra-azacyclo -tetradecinato(2-)}nickel(II) and of {7,8,15 16,17,18-hexahydrodibenzo[e,m][1,4,8,11] tetra-aza-cyclo-tetradecinato{2-)} nickel(II). J. Chem. Soc. (Dalton), 1799-1803 (1974).
  29. Hall, S.R., Maslen, E.N. and Cooper, A. The crystal and molecular structure of 3a,6a-dihydroxy-5b-cholan-24-oic acid, C24O4H40. Acta Cryst. B30, 1441-1447 (1974).
  30. Maslen, E.N., Cannon, J.R., White, A.H. and Willis, A.C. The crystal structure of 3-methyl-5-phenylpyrazole. J. Chem. Soc. (Perkin II), 1298-1301 (1974).
  31. Maslen, E.N., Raston, C.L. and White, A.H. Crystal structure of bis(2,2':6',2'-terpyridyl)cobalt(II) bromide trihydrate. J. Chem. Soc. (Dalton), 1803-1807 (1974).
  32. Brotherton, P.D., Wege, D., White, A.H. and Maslen, E.N. Crystal and molecular structure of tetracarbonyl–(7,7-dimethoxynorborn-2-ene)chromium(0). J. Chem. Soc. (Dalton), 1876-1878 (1974).
  33. Maslen, E.N., Dewan, J.C., Kepert, D.L., Trigwell, K.R. and White, A.H. Stereochemistry of the MX4Y system (M = metal; X = unidentate, Y = bidentate ligand): Crystal structure of tetrachloro-[1,2-bis(dimethylarsino)-3,3,4,4 -tetrafluorocyclobut-1-ene]rhenium(IV). J.Chem. Soc. (Dalton), 2128-2132 (1974).
  34. Maslen, E.N., Raston, C.L., Skelton, B.W. and White, A.H. Crystal structure of bis(hydrazine)bis(hydrazinecarboxylato) cobalt(II). Aust. J. Chem. 28, 739-744 (1975).
  35. Maslen, E.N., Raston, C.L. and White, A.H. Crystal structure of aqua(2,2':6',2':6',2''-quaterpyridyl)sulphitocobalt(III) nitrate monohydrate. J. Chem. Soc. (Dalton), 323-326 (1975).
  36. Maslen, E.N., Raston, C.L., White, A.H. and Yandell, J.K. Crystal structure of trans-aquabis(ethylenediamine)sulphitocobalt(III) perchlorate monohydrate. J. Chem. Soc. (Dalton), 327-329 (1975).
  37. Maslen, E.N., Greaney, T. M., Raston, C.L. and White, A.H. The crystal structure of catena-di-m-acetylacetonato-cadmium(II). J. Chem. Soc. (Dalton), 400-402 (1975).
  38. Maslen, E.N., Toia, R.F., White, A.H. and Willis, A.C. Crystal structure of (5E,12E)-7b-acetoxybertya-5,12-diene-3,14-dione. J. Chem.Soc. (Perkin II), 1684-1689 (1975).
  39. Greaney, T.M., Raston, C.L., White, A.H. and Maslen, E.N. Crystal structure of potassium tris(acetylacetonato)cadmate(II) monohydrate. J. Chem. Soc. (Dalton), 876-879 (1975).
  40. Maslen, E.N., Sheppard, P.N., White, A.H. and Willis, A.C. Crystal structure of the tricyclic diterpene derivative 18-hydroxydecipia-2(4), 14-dien-1-oic acid. J. Chem. Soc. (Perkin II), 263-266 (1976).
  41. Maslen, E.N., Raston, C.L. and White, A.H. Crystal structure of an epoxycembradienol, 3,15-epoxy-4-hydroxycembra-7(Z),11(Z)-diene. Tetrahedron, 33, 3305-3311 (1977).
  42. Maslen, E.N., Raston, C.L. and White, A.H. Crystal structure of (Z)-cembr-4-ene-15,19,20-triol. Aust. J. Chem. 30, 2723 – 2727 (1977).
  43. Baker, E., Maslen, E.N., Watson, K.J. and White, A.H. Crystal and molecular structure of the ferrous ion complex of A23187. J. Amer. Chem. Soc. 106, 2860-2864 (1984).

General diffraction matters

  1. Maslen, E.N. An X-ray collimator for single crystal goniometers. J. Sci. Instrum. 35, 110-111 (1958).
  2. Abrahamsson, S. and Maslen, E.N. The use of diverging functions in the solution of three-dimensional Patterson syntheses. Z. Krist. 118, 1-32 (1963).
  3. Rae, A.I.M. and Maslen, E.N. An analysis of possible methods for refining a non-centrosymmetric structure containing a partial centre of symmetry. Acta Cryst. 16, 703-704 (1963).
  4. Paton, M.G. and Maslen, E.N. The scattering length of ytttrium for thermal neutrons. Acta Cryst. 19, 679-680 (1965).
  5. Hall, S.R. and Maslen, E.N. An experimental determination of Df” for iodine. Acta Cryst. 20, 383-389. (1966).
  6. Maslen, E.N. A method for allowing for thermal anisotropy in evaluating Wilson plots and normalised structure factors. Acta Cryst. 22, 945-946 (1967).
  7. Maslen, E.N. An expression for the temperature factor of a librating atom. Acta Cryst. A24, 434-437 (1968).
  8. Maslen, E.N. The refinement of structures with non-crystallographic molecular symmetry. Acta Cryst. B24, 1165-1170 (1968).
  9. Maslen, E.N. A phase refinement of the crystal structure of benzotrifuroxan. Acta Cryst. B24, 1170-1172 (1968).
  10. Maslen, E.N. On the accuracy of electron density distributions with particular reference to structures with non-crystallographic molecular symmetry. Acta Cryst. B24, 1172-1175 (1968).
  11. Maslen, E.N. Higher order mechanistic models for thermal motion in crystal structures. Crystallographic Computing. Copenhagen: Munksgaard, pp. 227-242 (1970).
  12. Maslen, E.N. The effect of models for thermal motion and two-centre scattering on charge density analysis. Acta Cryst. A28, S8 (1972).
  13. Maslen, E.N. A procedure for the refinement of accurate diffraction data from molecular crystals. Acta Cryst. A25, S126 (1969).
  14. Delaney, W.T., Furina, R., Maslen, E.N., Price, P.F. and Varghese, J.N. Population analysis of molecular crystals: – density function or error sponge? Conference 'Diffraction studies of real atoms and real crystals'. Abstract 45. I.U.Cr. and Australian Academy of Science (1974).
  15. Davis, C.L., Maslen, E.N. and Varghese, J.N. Minimizing the variance in densities evaluated by Fourier synthesis. Acta Cryst. A34, 371-377 (1978).
  16. Davis, C.L. and Maslen, E.N. Minimizing the variance in integrals and derivatives of the electron density. Acta Cryst. A34, 743-746 (1978).
  17. Coppens, P., Dam, J., Harkema, S., Feil, R., Lehmann, M.S., Goddard, R., Kruger, C., Hellner, E., Johansen, H., Larsen, F.K., Koetzle, T.F., McMullan, R.K., Maslen, E.N. and Stevens, E.D.I.U.Cr. Commission on Charge, Spin and Momentum Densities. Project on comparison of structural parameters and electron density maps of
    oxalic acid dihydrate. Acta Cryst. A40, 184-195 (1984).
  18. Maslen, E.N. Problems in high precision electron density studies. Methods and applications in crystallographic computing: Proceedings of the International Summer School on Crystallographic Computing, Kyoto. Oxford: Clarendon Press, pp. 333-340 (1984).
  19. Spadaccini, N. and Maslen, E.N. Extinction in the KMF3 perovskites. Acta Cryst. A43, C-104 (1987).
  20. Maslen, E.N. The statistical significance of difference densities. Acta Cryst. A44, 33-37 (1988).
  21. Maslen, E.N., Fox, A.G. and O'Keefe, M.A. Section 6.1.1. X-ray scattering. In: International Tables for Crystallography. Volume C – Mathematical, Physical and Chemical Tables (Dordrecht: Kluwer), 476-516 (1992).
  22. Maslen, E.N. Section 6.3 X-ray absorption. In: International Tables for Crystallography. Volume C – Mathematical, Physical and Chemical Tables (Dordrecht: Kluwer), 520-529 (1992).
  23. Maslen, E.N. When automatic structure solution fails. Communicatedabstracts OCM-04.03.04. Acta Cryst. A49, 138-139 (1993).
  24. Streltsov, V.A. and Maslen, E.N. On least squares estimation of extinction corrections. Acta Cryst. A48, 651-653 (1992).
  25. Maslen, E.N. and Spadaccini, N. Corrections for extinction from equivalent reflection intensities. Asian Crystallographic Association Inaugural Meeting, Singapore. Acta Cryst. A49, Abstract 15V-63 (1992).
  26. Maslen, E.N., Streltsov, V.A., Ishizawa, N. and Satow, Y. Synchrotron x-ray study of the electron density in corundum a-Al2O3. Asian Crystallographic Association Inaugural meeting, Singapore. Acta Cryst. A49, Abstract 15V-68 (1992).
  27. Maslen, E.N. and Streltsova, N.R. On the reproducability of electron density maps for ideal perovskites. Asian Crystallographic Association Inaugural meeting, Singapore. Acta Cryst. A49, Abstract 15V-76 (1992).
  28. Maslen, E.N., Streltsov, V.A., Streltsova, N.R., Ishizawa, N. and Satow, Y. Synchrotron X-ray study of the electron density in a-Al2O3. Acta Cryst. B49, 973-980 (1993).
  29. Maslen, E.N., Spadaccini, N., Ito, T., Marumo, F., Tanaka, K. and Satow, Y. A synchrotron radiation study of potassium zinc fluoride perovskite. Acta Cryst. B49, 632-636 (1993).
  30. Maslen, E.N. and Spadaccini, N. Extinction corrections from equivalent reflections. Acta Cryst. A49, 661-667 (1993).
  31. du Boulay, D. and Maslen, E.N. Absorption, extinction and dead-time correction for high precision imaging with synchrotron sources. Acta Cryst. A49, 376, Abstract PS-14.01.12 (1993).

Electron density and bonding

  1. Rae, A.I.M. and Maslen, E.N. The importance of the imaginary part of the scattering factor of bonded carbon. Acta Cryst. 19, 1061-1063 (1965).
  2. Rietveld, E.G., Maslen, E.N. and Clews, C.J.B. An X-ray and neutron diffraction refinement of the structure of p-terphenyl. Acta Cryst. B26, 693-706 (1970).
  3. O'Connell, A.M., Rae, A.I.M. and Maslen, E.N. A discussion of the distribution of bonded electron density. Acta Cryst. 21, 208-219 (1966).
  4. O'Connor, B.H. and Maslen, E.N. The electron density distribution in 1,3,5-triacetylbenzene. Acta Cryst. B30, 383-389 (1973).
  5. Allen-Williams, A.J., Delaney, W.T., Furina, R., Maslen, E.N., O'Connor, B.H., Varghese, J.N. and Yung Fook Hong. Charge density analyses for molecular crystals using Bragg diffraction data: the effects of error. Acta Cryst. A31, 101-115 (1975).
  6. Price, P.F., Maslen, E.N. and Moore, F.H. Electron-density studies. I. A neutron diffraction powder study of diamond. Acta Cryst. A34, 171-172 (1978).
  7. Price, P.F. and Maslen, E.N. Electron-density studies. II. Further comments on the electron density in diamond. Acta Cryst. A34, 173-183 (1978).
  8. Price, P.F., Maslen, E.N. and Mair, S.L. Electron-density studies. III. A re-evaluation of the electron distribution in crystalline silicon. Acta Cryst. A34, 183-193 (1978).
    82a. Price, P.F., Maslen, E.N. and Mair, S.L. Detailed charge density studies of crystalline silicon. International Union of Crystallography Xth International Congress. Abstract 17.3.11, S225 (1975).
  9. Price, P.F., Maslen, E.N. and Delaney, W.T. Electron densities. IV. A comparison of techniques for charge density analysis and their application to s-triazine. Acta Cryst. A34, 194-203 (1978).
  10. Price, P.F., Varghese, J.N. and Maslen, E.N. Electron density studies. V. The electron density in melamine (2,4,6-triamino-s-triazine) with and without exponent refinement. Acta Cryst. A34, 203-216 (1978).
    84a. Varghese, J.N., O'Connell, A.M. and Maslen, E.N. The X-ray and neutron crystal structure of 2,4,6-triamino-1,3,5-triazine (melamine). Acta Cryst. B33, 2102-2108 (1977).
  11. Maslen, E.N. Electron density, chemical bonding and solid state interactions. Acta Cryst. A34, S27 (1978).
  12. Maslen, E.N., Ridout, S.C., Varghese, J.N., and White, A.H. Electron density distributions in transition metal complexes. Acta Cryst. A34, S21 (1978).
  13. Maslen, E.N. Applications of electron density studies to complexes of the transition metals. In: Electron and magnetization densities in molecules and crystals, ed. P. Becker (NATO Advanced Study Institute Series B: Physics, Volume 48). New York: Plenum Press, pp.779-789 (1980).
  14. Varghese, J.N. and Maslen, E.N. Electron density in non-ideal metal complexes. I. Copper sulphate pentahydrate. Acta Cryst. B41, 184-190 (1985).
  15. Maslen, E.N., Spadaccini, N., Watson, K.J. and White, A.H. Electron density in non-ideal metal complexes. II. Sodium bis(carbonato)cuprate(II). Acta Cryst. B42, 430-436 (1986).
  16. Maslen, E.N., Spadaccini, N. and Watson, K.J. Electron density distribution in potassium bis(carbonato)cuprate(II). Proc. Indian Acad. Sci. (Chem. Sci.) 92, 443-448 (1983).
  17. Maslen, E.N. and Ridout, S.C. Electron density in non-ideal metal complexes. III. Bis(hydrazine)bis(hydrazinecarboxylato)cobalt(II). Acta Cryst. B43, 352-356 (1987).
    91a. Maslen, E.N., Ridout, S.C. and White, A.H. The electron distribution in bis(hydrazine)-bis(hydrazinecarboxylato)cobalt(II). International Union of Crystallography Xth International Congress. Abstract 17.3.10, S225 (1975).
  18. Vaalsta, T.P. and Maslen, E.N. Electron density in chromium sulfate pentahydrate. Acta Cryst. B43, 448-454 (1987).
  19. Maslen, E.N. and Spadaccini, N. Electron density in potassium bis(dithiooxalato-S,S')nickelate(II). Acta Cryst. B43, 461-465 (1987).
  20. Hester, J.R., Maslen, E.N., Glazer, A.M. and Stadnicka, K. Jahn-Teller distortion of the electron density in a-nickel sulfate hexahydrate. Acta Cryst. B49, 641-646 (1993).
  21. Maslen, E.N., Ridout, S.C., Watson, K.J. and Moore, F.H. The structure of Tutton's salts. I. Diammonium hexa-aquamagnesium (II) sulfate. Acta Cryst. C44, 409-412 (1988).
  22. Maslen, E.N., Ridout, S.C. Watson, K.J. and Moore, F.H. The structure of Tutton's salts. II. Diammonium hexa-aquanickel(II) sulfate. Acta Cryst. C44, 412-415 (1988).
  23. Maslen, E.N., Watson, K.J., Ridout, S.C. and Moore, F.H. Electron density in diammonium hexa-aquazinc(II) sulfate – an X-ray and neutron study. Acta Cryst. C44, 1510-1514 (1988).
  24. Maslen, E.N., Watson, K.J. and Moore, F.H. Crystal structure and electron density of diammonium hexa-aquacopper (II) sulfate. Acta Cryst. B44, 102-107 (1988).
  25. Maslen, E.N., Ridout, S.C. and Watson, K.J. Electron density in non-ideal metal complexes. IV. Hexa-aquametal(II) ammonium sulphates. Acta Cryst. B44, 96-101 (1988).
  26. Chatterjee, A., Maslen, E.N. and Watson, K.J. The effect of the lanthanoid contraction on the nona-aqualanthanoid(III) tris(trifluoromethanesulfonates). Acta Cryst. B44, 381-386 (1988).
  27. Chatterjee, A., Maslen, E.N. and Watson, K.J. Electron densities in crystals of nona-aqualanthanoid(III) tris(trifluoromethanesulphonates). Acta Cryst. B44, 386-395 (1988).
  28. Buttner, R.H. and Maslen, E.N. Electron difference density in KZnF3 perovskite. Z. Krist. 185, 656 (1988).
  29. Buttner, R.H. and Maslen, E.N. Electron difference density in potassium zinc fluoride perovskite. Acta Cryst. C44, 1707-1709 (1988).
  30. Maslen, E.N. and Spadaccini, N. Electron density, thermal motion and bonding interactions in the perovskite structures KMF3 with M = Mn, Fe, Co and Ni. Acta Cryst. B45, 45-52 (1989).
  31. Buttner, R.H., Maslen, E.N. and Spadaccini, N. Structure, electron density and thermal motion of KCuF3. Acta Cryst. B46, 131-138 (1990).
  32. Buttner, R.H., Maslen, E.N. and Spadaccini, N. A position-space model for superconductivity in YBa2Cu3O7-x. Acta Cryst. B48, 21-30 (1992).
  33. Buttner, R.H. and Maslen, E.N. Structural parameters and electron difference density in Y2BaCuO5. Acta Cryst. B49, 62-66 (1993).
  34. Hsu, R.M., Maslen, E.N. and Ishizawa, N. A synchrotron X-ray study of the electron density in Y2BaCuO5. Acta Cryst. B52, 569-575 (1996).
  35. Hsu, R.M. and Maslen, E.N. A synchrotron X-ray study of Dr in Y2BaCuO5. Asian Crystallographic Association Inaugural meeting, Singapore. Acta Cryst. A49, Abstract 15V-69 (1992).
  36. Hester, J., Hsu, R. and Maslen, E.N. Second-nearest-neighbour interactions and the electron density in Y2BaCuO5. Acta Cryst. A49, Abstract PS-14.02.13, 381-382 (1993).
  37. Hsu, R. and Maslen, E.N. Effect of second-nearest-neighbour interactions on the electron density in Y2BaCuO5 and LiTaO3. Crystal XIX: Meeting of the Society of Crystallographers in Australia (Ballarat). Abstract P15 (1995).
  38. Buttner, R.H. and Maslen, E.N. Electron difference density and vibration tensors in SrTiO3. Acta Cryst. B48, 639-644 (1992).
  39. Buttner, R.H. and Maslen, E.N. Electron difference density and structural parameters in CaTiO3. Acta Cryst. B48, 644-649 (1992).
  40. Buttner, R.H. and Maslen, E.N. Structural parameters and electron difference density in BaTiO3. Acta Cryst. B48, 764-769 (1992).
  41. Maslen, E.N., Streltsov, V.A. and Streltsova, N.R. (I.) X-ray study of the electron density in calcite, CaCO3. Acta Cryst. B49, 636-641 (1993).
  42. Maslen, E.N., Streltsov, V.A. and Streltsova, N.R. (II.) X-ray study of the electron density in magnesite, MgCO3. Acta Cryst. B49, 980-984 (1993).
  43. Maslen, E.N., Streltsov, V.A., Streltsova, N.R. and Ishizawa, N. Electron density and optical anisotropy in rhombohedral carbonates. III. Synchrotron X-ray studies of CaCO3, MgCO3 and MnCO3. Acta Cryst. B51, 929-939 (1995).
  44. Maslen, E.N., Streltsov, V.A. and Streltsova, N.R. X-ray study of the electron density in rhombohedral carbonates, CaCO3, MgCO3, MnCO3. Acta Cryst. A49, Abstract PS-14.02.15, 382-383 (1993).
  45. Ishizawa, N., Maslen, E.N., Streltsov, V.A. and Streltsova, N.R. Diffraction study of the electron density and optical anisotropy in rhombohedral carbonates. Photon Factory Activity Report 1993, Vol. 11, p. 305 (1994).
  46. Maslen, E.N., Streltsov, V.A. and Streltsova, N.R. Synchrotron X-ray study of electron density and optical anisotropy in rhombohedral carbonates. Crystal XVIII: Meeting of the Society of Crystallographers in Australia (Medlow Bath). Abstract p. 33 (1994).
  47. Hester, J.R., Maslen, E.N., Spadaccini, N., Ishizawa, N. and Satow, Y. Electron density in potassium tetrachloropalladate (K2PdCl4) from synchrotron radiation data. Acta Cryst. B49, 842-846 (1993).
  48. Hester, J.R., Maslen, E.N., Spadaccini, N., Ishizawa, N. and Satow, Y. Accurate synchrotron radiation Dr maps for K2SiF6 and K2PdCl6. Acta Cryst. B49, 967-973 (1993).
  49. Hester, J.R., Maslen, E.N., Spadaccini, N., Ishizawa, N. and Satow, Y. Synchrotron radiation vibration amplitudes and Dr maps for K2SiF6 and K2PdCl4. Asian Crystallographic Association Inaugural meeting (Singapore). Abstract 15V-67 (1992).
  50. Hester, J.R. and Maslen, E.N. Electron density – structure relationships in some perovskite-type compounds. Acta Cryst. B51, 913-920 (1995).
  51. Maslen, E.N. and Streltsov, V.A. Electron density imaging with synchrotron radiation. AsCA'95: 2nd Conference of the Asian Crystallographic Association (Bangkok). Abstract 1A14 (1995).
  52. Maslen, E.N., Streltsov, V.A., Streltsova, N.R. and Ishizawa, N. Synchrotron X-ray study of the electron density in a-Fe2O3. Acta Cryst. B50, 435-441 (1994).
  53. Maslen, E.N., Spadaccini, N., Ito,T., Marumo, F. and Satow, Y. A synchrotron radiation study of strontium titanate. Acta Cryst. B51, 939-942 (1995).
  54. du Boulay, D., Maslen, E.N., Streltsov, V. A. and Ishizawa, N. A synchrotron X-ray study of the electron density in YFeO3. Acta Cryst. B51, 921-929 (1995).
  55. du Boulay, D., Maslen, E.N. and Streltsov, V.A. A synchrotron X-study of the electron densitry in YFe2O3. Proceedings of IC'94. (Roy. Aust. Chem. Inst.) D49 (1994).
  56. du Boulay, D. and Maslen, E.N. The structural variation within the rare earth orthoferrites and aluminates. Proceedings of IC'94. (Roy. Aust. Chem. Inst.) D50 (1994).
  57. du Boulay, D. and Maslen, E.N. Structure and electron density in rare earth aluminates and orthoferrites. Crystal XIX: Meeting of the Society of Crystallographers in Australia (Ballarat). Abstract WPM2.3 (1995).
  58. Hsu, R., Maslen, E.N., Streltsov,V.A. and Ishizawa, N. Synchrotron radiation imaging of the deformation electron density in LiNbO3 and LiTaO3. AsCA'95: 2nd Conference of the Asian Crystallographic Association (Bangkok). Abstract 3P42 (1995).
  59. Maslen, E.N., Streltsov, V.A. and Ishizawa, N. A synchrotron X-ray study of the electron density in C-type rare earth oxides. Acta Cryst. B52, 414-422 (1996).
  60. Maslen, E.N. and Streltsov, V.A. Synchrotron X-ray study of the electron density in C-type rare earth oxides. Crystal XIX: Meeting of the Society of Crystallographers in Australia (Ballarat). Abstract P29 (1995).
  61. Maslen, E.N., Streltsov, V.A. and Ishizawa, N. A synchrotron X-ray study of the electron density in SmFeO3. Acta Cryst. B52, 406-413 (1996).
  62. Etschmann, B.E., Maslen, E.N. and Streltsova, N.R. Deformation densities in simple rare earth compounds. Acta Cryst. A49, Abstract PS-14.02.14, 382 (1993).
  63. Streltsov, V.A. and Maslen, E.N. Synchrotron electron density-property relationship for metal oxides. IUCr synchrotron radiation satellite meeting, Argonne National Laboratory. Abstract, 111-03, p. 29 (1996).
  64. Maslen, E.N., Streltsov, V.A., Streltsova, N.R. and Ishizawa, N. Synchrotron X-ray density in the layered LaOCl structure. Acta Cryst. B52, 576-579 (1996).
  65. Milne, A.M. and Maslen, E.N. Electron density in the spin crossover complex trans-[N.N'-ethylenebis(salicylidenaminato)] bis(imidazole)iron(III) perchlorate. Acta Cryst. B44, 254-259 (1988).
  66. Chantler, C.T. and Maslen, E.N. Charge transfer and three-centre bonding inmonoprotonated and diprotonated 2,2'-bipyridylium decahydro-closo-decaborate(2-). Acta Cryst. B45, 290-297 (1989).

The promolecule

  1. Maslen, E.N. and Spackman, M.A. Atomic charges and electron density partitioning. Aust. J. Phys. 38, 273-287 (1985).
  2. Spackman, M.A. and Maslen, E.N. Chemical properties from the promolecule. J. Phys. Chem. 90, 2020-2027 (1986).
  3. Spackman, M.A. and Maslen, E.N. An empirical estimate of the correlation energy. Chem. Phys. Letters 126, 19-25 (1986).
  4. Trefry, M.G., Maslen, E.N. and Spackman, M.A. Electrostatic, Madelung and cohesive energies for solids. J. Phys. C: Solid State Phys. 20, 19-28 (1987).
  5. Henderson, J.A. and Maslen, E.N. Atom size and charge in alkali halides. Acta Cryst. A43, C-102 Abstract 06.2-1 (1987).
  6. Maslen, E.N. and Trefry, M.G. 3d-transition metals: Electron promotion and the independent atom model. J. Phys. Chem. Solids 49, 753-759 (1988).
  7. Spackman, M.A. and Maslen, E.N. Electron density and the chemical bond. A reappraisal of Berlin's theorem. Acta Cryst. A41, 347-353 (1985).
  8. Etschmann, B.E. and Maslen, E.N. Atomic charge in diatomic promolecules and in promolecular solids. Proceedings of IC'94. Roy. Aust. Chem. Inst. 1, D5 (1994).
  9. Etschmann, B.E. and Maslen, E.N. Atomic charges for promolecular solids. Crystal XVIII: Meeting of the Society of Crystallographers in Australia (Medlow Bath, N.S.W.). Abstract, Vol. 1, WPM1.2 (1994).
  10. Etschmann, B.E. and Maslen, E.N. Properties of the promolecule. IUCr XVII Congress, Seattle, USA. Acta Cryst. A53 Abstract PS.09.02.07, C-352 (1996).
    150a. Maslen, E.N. and Etschmann, B.E. Bonding without Ionisation. Aust. J. Phys. 53, 299-316 (2000).
  11. Etschmann, B.E. and Maslen, E.N. Atomic radii from electron densities. Crystal XIX: Meeting of the Society of Crystallographers in Australia (Ballarat, Victoria). Abstract P5 (1995).
  12. Maslen, E.N. and Etschmann, B.E. Atomic radii from electron densities. AsCA'95: 2nd Conference of the Asian Crystallographic Association (Bangkok, Thailand). Abstract 3P46 (1995).
    152a. Etschmann, B.E. and Maslen, E.N.). Atomic Radii from Electron Densities. Aust. J. Phys. 53, 317-332 (2000).

Theoretical chemistry

  1. Davis, C.L., Maslen, E.N. and Varghese, J.N. On exact analytical solutions for the few-particle Schrodinger equation. I. A perturbation study. Proc. Roy. Soc. A384, 57-88 (1982).
  2. Davis, C.L. and Maslen, E.N. On exact analytical solutions for the few-particle Schrodinger equation. II. The ground state of helium. Proc. Roy. Soc. A384, 89-105 (1982).
  3. Davis, C.L. and Maslen, E.N. On exact analytical solutions for the few-particle Schrodinger equation. III. Spatially symmetric S states of two identical particles in the field of a massive third partricle. J. Phys. A: Math. Gen. 16, 4237-4253 (1983).
  4. Davis, C.L. and Maslen, E.N. On exact analytical solutions for the few-particle Schrodinger equation. IV. The asymptotic form and normalizability of the wavefunction. J. Phys. A: Math. Gen. 16, 4255-4264 (1983).
  5. Davis, C.L. and Maslen, E.N. Series wave functions for the helium atom. Int. J. Quant. Chem. 17, 217-225 (1983).
  6. Abbott, P.C. and Maslen, E.N. Expansion of two-body potentials in hyperspherical harmonics. J. Phys. B: At. Mol. Phys. 17, L489-492 (1984).
  7. Gottschalk, J.N. and Maslen, E.N. Three-body S-state wavefunctions: symmetry and degrees of freedom associated withnormalisation of the exact wavefunction. J. Phys A: Math. Gen. 18, 1687-1696 (1985).
  8. Abbott, P.C. and Maslen, E.N. A model wavefunction including electron correlation for the ground state of the helium isoelectronic sequence. J. Phys. B: At. Mol. Phys. 19, 1595-1605 (1986).
  9. McIsaac, K., Gottschalk, J.E. and Maslen, E.N. Closed form expressions for an integral involving the Coulomb potential. J. Computational Physics, 67, 479-481 (1986).
  10. McIsaac, K. and Maslen, E.N. Exact wavefunctions for few-particle systems: the choice of expansion for Coulomb potentials. Int. J. Quant. Chem. 31, 361-368 (1987).
  11. Abbott, P.C. and Maslen, E.N. Coordinate systems and analytic expansions for 3-body atomic functions: I. Partial summation for the Fock expansion in hyperspherical coordinates. J. Phys. A: Math. Gen. 20, 2043-2075 (1987).
  12. Gottschalk, J.E., Abbott, P.C. and Maslen, E.N. Coordinate systems and analytic expansions for three-body atomic wavefunctions: II. Closed form wavefunctions to second order in r. J. Phys. A: Math. Gen. 20, 2077-2104 (1987).
  13. Gottschalk, J.E. and Maslen, E.N. Coordinate systems and analytic expansions for three-body atomic wavefunctions: III. Derivative continuity via solutions to Laplace's equation. J. Phys. A: Math. Gen. 20, 2781-2803 (1987).
  14. Gottschalk, J.E. and Maslen, E.N. Reduction formulae for generalised hypergeometric functions of one variable. J. Phys. A: Math. Gen. 21, 1983-1998 (1988).
  15. Maslen, E.N. and Trefry, M.G. Two-center molecular repulsion integrals over Slater functions. Int. J. Quant. Chem. 37, 51-68 (1990). Erratum. 38, 871-872 (1990).

General

  1. Maslen, E.N. X-ray physics in Western Australia. The Australian Physicist, February, 29-30 (1976).
  2. Maslen, E.N. A systems approach to computing for charge density studies. Computing in Crystallography: Proceedings of the International Union of Crystallography Computing School, Bangalore. Indian Institute of Sciences Publication 15.01-15.14 (1980).
  3. Allen, F.H., Bugg, C.E. and Maslen, E.N. Editorial, electronic submission and publication of structural results in Acta Crystallographica. Acta Cryst. A47, 637-639 (1991).
  4. Maslen, E.N. Promises and pitfalls in electronic information. Acta Cryst. A49, Abstract DS-18.03.05. 414 (1993).

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