Ab initio calculations of elastic and thermodynamic properties of fcc- 6LiF under high temperatures and pressures

The elastic and thermodynamic properties of fcc-(LiF)-Li-6 under high temperatures and pressures are investigated using the ab initio method and quasi-harmonic Debye model. The lattice constant of (LiF)-Li-6 at ground state is a little larger than that of LiF. When pressure is less than 10 GPa, crystal lattice is compressed easily at low temperature, and when P > 10 GPa, lattice can be compressed easily at high temperature. C-11 increases with pressure and reduces with temperature sensitively. C-12 and C-44 raise or decrease just a little with increasing pressure and temperature. Heat capacity of different pressure increases with temperature and closes to the Du long-Petit limit at higher temperatures. Debye temperature decreases with temperature, and increases with pressure. Furthermore, under lower pressure, thermal expansion coefficient raise rapidly with temperature, and the increasing trend will get slow at higher pressure.