Self-Consistent-Field Approach to Lattice Dynamics

The self-consistent-field theory of lattice dynamics is examined with particular emphasis on the physical assumptions entering this approach. The solution of the basic equation is generalized beyond that of earlier treatments to include damping and the corresponding frequency shifts of the collective modes. The expressions found for the damping and frequency shifts contain renormalized anharmonic force constants but otherwise are essentially the same as those derived in conventional perturbation theory.