A molecular dynamics study of structural and dynamical correlations of CaTiO3

An effective interatomic potential which can be used to describe perovskite-type CaTiO3 in molecular dynamics (MD) simulations is proposed. The potential proposed consists of two-body interactions, which include steric repulsions due to atomic sizes, Coulomb interactions resulting from charge transfer between particles, and charge-induced dipole interactions due to the electronic polarizability of ions and dipole-dipole (van der Waals) attraction. The energetics of the three crystalline forms of CaTiO3 were calculated: the orthorhombic-Pbnm structure had the lowest energy, followed by the tetragonal-I4/mcm and cubic-Pm3m structures. The two phase transitions induced by temperature change were characterized through anomalies in the lattice parameters, elastic constants, bulk modulus, bond-angle distribution and the intensity of the first peak of the partial pair distribution function, gCa-O(r). Analysis of the pair distribution function is a sensitive means of detecting structural transformation in materials caused by small distortions. It is shown that the rise in structural symmetry with temperature is actually due to the tilting of the TiO6 polyhedra. The response of the system to external pressure was also analyzed. Extremely high pressure, up to 300 GPa, was applied and no significant modification attributable to a major structural change was observed. The proposed interatomic potential is in good agreement with experimental data, predicting the melting point, phonon vibrational density of sates, thermal expansion coefficient and specific heat at constant volume. The recrystallized polycrystalline CaTiO3 was reproduced in the simulation by cooling the liquid. It is shown that the presence of grain boundaries in the material is essential to reproduce the experimental data correctly.