1ST-ORDER ANHARMONIC CORRECTION TO THE FREE-ENERGY OF A COULOMB CRYSTAL IN PERIODIC BOUNDARY-CONDITIONS

The free energy of the classical one-component plasma is calculated analytically in the crystalline phase for both fcc and bcc lattices to O(T2), where T is the temperature. By application of thermodynamic perturbation theory, we explicitly evaluate the effect of three- and four-phonon interactions on the partition function. Periodic boundary conditions are applied to make contact with previous numerical work, in which the O(T2) term was assumed to be negligible. We find that it is much larger than previously thought. This increases the thermodynamic stability of the crystal phase over previous estimates. © 1990 The American Physical Society.