High-pressure lattice dynamics and thermodynamic properties of Th:: An ab initio study of phonon dispersion curves

Phonon dispersion curves and thermodynamics of actinides are hardly accessible for both theory and experiments. In this paper we present an ab initio study of the thermodynamics properties of thorium within the framework of the quasiharmonic approximation and by using density-functional theory and the pseudopotential method. First we compare the phonon spectrum we obtained at zero pressure with inelastic neutron scattering experiments. Thereafter we use the phonon dispersions to obtain the PVT equations of state and derive thermodynamic quantities from the free energy. Then we compare our results for the thermal volume expansion, bulk modulus, heat capacity, or Debye temperature with experimental values when existing. The results show a promising agreement with experiment and propose several predictive behaviors.