Investigation of Vibrational and Thermodynamic Characteristics of ThC Under High Pressure and Temperature

In this paper, the structural, thermodynamic properties and phonon dispersion of thorium carbide are investigated through the density functional theory and the density-functional perturbation theory by using ab initio calculations within the framework of the plane-wave method. Ultrasoft pseudopotentials with GGA-PBE functional are utilized for the exchange and correlation potential. Thermodynamic properties of ThC are studied for the first time under the quasi-harmonic Debye-Gruneisen model as was implemented in the GIBBS2 code. Structural properties including lattice constant (a0), bulk modulus (B0) and the first derivative of the bulk modulus (B0') are calculated by fitting the third-order Birch-Murnaghan equation of state and compared to other theoretical and experimental works that revealed a good agreement. The phonon band structure is calculated from the density-functional perturbation theory for the lattice constant and investigated experimentally and the obtained phonon gap was about 185 cm-1. It was observed that the Debye temperature decreases with increasing the temperature at a constant pressure while it increases with increasing the pressure for all temperatures. The Vibrational Helmholtz free energy, the Gibbs free energy, the adiabatic bulk modulus, and the isothermal bulk modulus decreased with increasing the temperature at a given pressure.