Ab initio investigations on lattice dynamics and thermal characteristics of ThO2 using Debye–Einstein model

In this study, the lattice dynamics and thermal characteristics of thorium dioxide are calculated using the first-principle calculations based on the density functional theory (DFT). The Gibbs free energy, isothermal bulk moduli, Debye temperature, thermal Gruneisen parameter as well as vibrational contributions of Helmholtz free energy, internal energy and entropy of thorium dioxide are studied for the first time under high temperatures and pressures. Thermal properties are compared using generalized gradient approximation (GGA) and local density approximation (LDA) under a novel model based on the quasi-harmonic Debye–Einstein method. The results of the simulation reveal that the lattice constant calculated by LDA is less than the one calculated by GGA, while the Gibbs free energy, Debye temperature, adiabatic and isothermal bulk modulus obtained from LDA are greater than ones obtained from GGA. The volumetric thermal expansion coefficient and vibrational contribution of entropy obtained from GGA and LDA increase with rise in temperature.