Quasiharmonic free energy and derivatives for three-body interactions

Quasiharmonic lattice dynamics applied to crystals of atoms interacting via general rotationally and translationally invariant short-ranged three-body forces is considered. Expressions for the static energy and its first and second derivatives, and the free energy and its first derivatives, are pres ented, where the differentiation is with respect to internal (atomic positi ons) and external (macroscopic deformation) strains. Some results of applyi ng the theory to cu quartz are given. The paper extends the work of Taylor et al. [M. B. Taylor et al., Phys. Rev. B 56, 14 380 (1997)] in which more careful consideration of the basic theory has been given, and detailed expr essions for pairwise short-ranged and Coulombic interactions were presented . [S0163-1829(99)00101-0].