Lattice Statistics of Hydrogen Bonded Crystals. II. The Slater KDP Model and the Rys F-Model

Abstract

The Slater KDP model, a simple hydrogen bonded ferroelectric model, and the Rys F‐model, a simple hydrogen bonded antiferroelectric model, have been treated using both high‐ and low‐temperature series for the partition function. The high‐temperature series is a modification of the residual entropy of ice series discussed in I. For each model a temperature is found at which the high‐temperature series and the low‐temperature series are identically equal. For the KDP model this equality gives a transition temperature and a latent heat is easily calculated, both of which are exact. It so happens that these exact results agree with previous analyses which used only mean field approximations. For the F‐model the formal equality of the series gives the first evidence for a phase transition. Although the latent heat calculation throws some doubt on the existence of a transition, after further discussion of the series it is concluded that there most probably is a phase transition.