Interpretation of EXAFS in ReO₃ using molecular dynamics simulations

Temperature dependent Re L₃-edge EXAFS signals from perovskite-type cubic ReO₃ have been successfully interpreted using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering approach. The force field model, required for MD simulations, has been determined by fitting the Re-O and O-O pairwise interatomic potentials to a set of experimental data (lattice parameter, elastic constants and bulk modulus) and phonon frequencies, theoretically calculated from the first principles at high symmetry points of the Brillouin zone. The MD simulations reproduce well the anisotropy of thermal vibration for oxygen atoms and confirm a deviation of the mean Re-O-Re angle from 180°. The atomic configurations from the MD simulations have been used to calculate the configuration-averaged EXAFS spectra at several temperatures. The use of the MD results allows a straightforward treatment of thermal disorder in the multiple-scattering contributions to the total EXAFS signal. Good agreement between calculated and experimental EXAFS signals has been found, that additionally supports the accuracy of our force field model.