Polarization fluctuations in ferroelectric models

We consider the relation between the finite-wave-vector susceptibility (q) of the six-vertex model family and the macroscopic susceptibility. This is nontrivial because (q) is singular at q=0. Using exact results for the macroscopic susceptibility, we infer the analytic form of the anisotropy parameter appearing in the pair-correlation function at large separation. Proceeding phenomenologically, we consider the effect of relaxing the ice rules, and the effect of short-ranged interactions other than the ice rules (e. g. , polarization gradient energies).