Theoretical investigation of structural and thermo-mechanical properties of thoria up to 3300 K temperature

Abstract

We investigated thermo-mechanical properties of thoria up to a very high temperature (3300 K). We demonstrate that, using first-principles molecular dynamics, it is possible to predict thermal expansion of thoria in agreement with experiment. The new generalized gradient approximation functional within the density functional theory predicts, in agreement with experiment, not only the relative thermal expansion but also the absolute values of the lattice constant as a function of temperature. The molecular dynamics approach has an advantage over the previously used quasi-harmonic method, because it can be used even at temperatures (above 2700 K) where the longitudinal optical mode breaks in thoria. The calculated phonon dispersion agrees well with the experimental relation, measured using inelastic neutron scattering. The temperature, at which the negative frequency in the optical mode appears, coincides with the λ-type pre-melting transition reported in thoria.