  Lattice dynamics and molecular dynamics studies of the oxides UO2 and Li2O in
their normal as well as superionic phase are reported. Lattice dynamics
calculations have been carried out using a shell model in the quasiharmonic
approximation. The calculated elastic constants, phonon frequencies and
specific heat are in good agreement with reported experimental data, which help
validate the interatomic potentials required for undertaking molecular dynamics
simulations. The calculated free energies reveal high pressure fluorite to
cottunite phase transitions at 70 GPa for UO2 and anti-fluorite to
anti-cotunnite phase transformation at 25 GPa for Li2O, in agreement with
reported experiments. Molecular dynamics studies shed important insights into
the mechanisms of diffusion and superionic behavior at high temperatures. The
calculated superionic transition temperature of Li2O is 1000 K, while that of
UO2 is 2300 K.
