Vibrational Enthalpies of Solid Crystalline Materials

Abstract

Specific heat at constant pressure is traditionally a difficult thermodynamic quantity to obtain from first-principles calculations. While theoretical avenues to Cp(T) do exist—most notably, the quasi-harmonic approximation—there are many materials for which this approximation is not valid. One of those materials is Ge. In this paper, we demonstrate how a new method—termed the Beyond Quasi-Harmonic method—takes into account all anharmonic vibrations by showing how our results are significantly better than those achieved through using the quasi-harmonic model. In addition, we calculate Cp(T) for 3C-SiC, a material for which there are surprisingly few experimental results. For 3C-SiC, our results agree well with the available experiments, and for Ge, our results agree very well with the generally accepted values.

Keywords

• Beyond Quasi-Harmonic method
• specific heat
• heat capacity
• supercell preparation
• vibrational enthalpy
• vibrational energy