Landau potential of a KDP crystal in the cluster approximation of the pseudospin model

Abstract

A relation between the microscopic and phenomenological descriptions of the ferroelectric phase transition in a KDP crystal has been considered. The microscopic description has used the pseudospin model in the cluster approximation taking into account tunneling of a proton on a hydrogen bond and yields the Landau potential. The temperature dependence of the coefficients of the first terms in the expansion of the Landau potential in powers of a small order parameter is presented graphically. The calculation results are given for positive and negative values of the long-range interaction parameter γ of the microscopic theory, and their difference is emphasized.