The Effect of Model Cluster Expansion on the Results of Microscopic Description of the Properties of KDP type H-Bonded Ferroelectrics

The results of model cluster expansion for qualitative description of thermodynamics of a structural phase transition and other properties and for elucidation of the effect of domain boundaries were analyzed within the framework of the Ising model in the single-domain cluster approximation with independent quantum chemical determination of all required pseudospin Hamiltonian parameters. For a number of dimeric model clusters, it was shown that their application for the KDP/DKDP crystals in the first case is of low use. The key result about fundamental changes in the electronic spectrum of the H-bonded subsystem in all studied dimeric clusters obtained by various calculations methods can be used to map out a plan for modeling a more realistic structure of domain boundaries with subsequent analysis of the obtained data by different statistical methods.