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Abstract: Geometric structure, atomic vibrations and atomic charges and their thermally induced fluctuations have been calculated as a function of depth in, and thickness of, rutile TiO2(110) slabs, within the framework of the variable-charge potential of Swamy and Gale [V. Swamy, J.D. Gale, Phys. Rev. B 62 (2000) 5406] at 300K. Molecular dynamics simulations and lattice dynamics calculations were performed with a 2D periodic slab model for slab thicknesses between 3 and 11 triple layers (approximately 9–35Å). Odd–even oscillations with respect to the number of slab layers are found for the surface relaxation for very thin slabs, and for the (slowly converging) rumpling in the middle of the slab. The Ti and O atomic charges in the outermost three atomic layers differ from the rest of the slab (they are less ionic); the thermal vibrations do not alter this picture. The atomic mean-square amplitudes are some 50% larger (more for O, less for Ti) at the surface than in the middle of the slab and decay rather slowly to the bulk values. Comparisons with the results of a rigid-ion potential for titania [M. Matsui, M. Akaogi, Mol. Simul. 6 (1991) 238] are presented for non-electronic properties. [Copyright &y& Elsevier]

Several Li+- and Na+-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN)n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Bo¨hm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li+(MeCN) and Na+(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li+ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na+ is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common. [Copyright &y& Elsevier]

Results from molecular dynamics simulations for bulk and the (0 1 1) surface of reduced and unreduced CeO2 at 300 K are reported. The presence of vacancies in reduced ceria is found to give rise to many different local structural arrangements, and to a significant broadening of the peaks in the pair-distribution function. This broadening is mainly due to the appearance of these new structural arrangements, and it is not due to the increased ionic motions in the reduced systems. [Copyright &y& Elsevier]