S. M. Tomlinson

Molecular dynamics studies of hydrocarbon diffusion in zeolites

Molecular dynamics simulation techniques have been used to investigate behaviour of sorbed CH4 and C2H4 in zeolite ZSM-5. Our calculations allowed for framework in addition to molecular motions. Diffusion trajectories were obtained for the sorbed molecules. Simulated diffusion coefficients were in acceptable agreement with experiment.

Defects in LiNbO3—II. Computer simulation

Abstract Results of our recent shell-model calculations concerning the most important intrinsic and extrinsic defect structures in LiNbO 3 are presented. Suitable energy minimization techniques involved in this simulation approach guarantee the full account of crystal relaxation effects upon defects. Li 3 O-deficiency, reduction-induced changes of the intrinsic defect structure as well as the incorporation modes of impurity ions may consistently be explained. Finally, a detailed description of the Mg incorporation over the whole solution range is given.

Interatomic potentials for oxides

Abstract We review the current status of potential models for oxide materials, with emphasis on the applications of potentials in simulation studies. We pay special attention to transition-metal oxides, silicates and ternary metal oxides. Extensions of potentials beyond the two-body formulation are discussed.

Atomistic simulation studies of technologically important oxides

The methodology for obtaining potential-energy function parameters by empirical procedures is discussed, and the strengths and limitations of the technique are highlighted. Studies of three important and structurally complex oxides using lattice-simulation techniques that incorporate the Mott–Littleton method, based upon empirically derived potentials are described. These are the high-Tc superconductor La2CuO4, the electro-optic device material LiNbO3 and the sensor and pigment material TiO2.

Industrial Applications of Simulation Studies in Solid State Chemistry

Abstract This paper gives an account of some recent applications of computer simulation techniques to materials of industrial importance. The methodology used is fully discussed, and applications to zeolites, high Tc superconductors, superionic conductors and mantle-forming minerals are described.

Studies of cation dopant sites in metal oxides by EXAFS and computer-simulation techniques

A combination of extended X-ray absorption fine structure (EXAFS) experiments and computer simulations has been used to probe the environments of cation dopants in three oxide systems of technological importance, viz. lithium niobate (a material with applications in non-linear optics), tin oxide (a component in some types of gas sensor) and rare-earth-dopod β″-alumina (crystals that exhibit novel optical properties). In Fe3+-doped LiNbO3 this work clearly locates the Fe3+ ions predominantly on the Li+ sites rather than on the Nb5+ sites and helps resolve a long-standing problem concerning the nature of the dopant environment. The preferred mode of solution of Ga3+ ions in SnO2 is found to be substitution for the host cations with O2– ion vacancies as the charge-compensating defects. At the concentration of dopant studied (a few mol%) the association of impurity ions and these defects, with the formation of clusters, is shown to be favoured. At this stage of the work the precise location of rare-earth dopants in β″-alumina is difficult; however, the present investigation indicates that a combination of molecular-dynamics simulations and EXAFS should prove a viable approach to this problem.

An EXAFS study of dopant substitution in LiNbO3 and LiTaO3

Abstract We report an EXAFS study of Co and Fe doped LiNbO3 and LiTaO3. Our results show that the dopant ions occupy Li sites in both materials.

Hole-pairing mechanisms in La2CuO4

The authors consider various possible hole-coupling mechanisms in the high-Tc superconductor, doped La2CuO4. Negative-U processes are energetically unfavourable. It is possible that bipolaronic species may be stabilised when antiferromagnetic energies and coupling terms arising from the distortions of the CuO6 octahedra are taken into account.

Deriving an Empirical Potential for Ferroelectric LiNbO3

Abstract We describe the derivation of a potential model for ferroelectric lithium niobate, by means of fitting parameters in the potential to the experimentally determined structure and properties of the material. In doing so we highlight the strengths and limitations of the technique, compared to theoretical methods for calculating the parameters. We also see that it is important to include ionic polarisation directly in the fit, owing to the role of polarisation in stabilising the ferroelectric structure.

A computational study of zeolite beta

Lattice energy minimisation procedures have confirmed the structure of zeolite beta as an intergrowth of two polymorphic structures.