QUANTUM-CHEMICAL APPROACH TO ZERO-DIMENSIONAL ANTIFERROELECTRICS AND QUANTUM PARAELECTRICS OF THE K_3H(SO_4)_2 FAMILY

摘要

The application of different quantum-chemical methods to the evaluation of coupling parameters of the Ising model (J_(ij)) is treated for the TKHS family crystals. Two approaches to the J_(ij) parameter evaluation are developed. The use of calculated J_(ij) values for the description of some distinctive features of the TKHS-like materials is discussed. The critical hydrogen concentrations (x_c) resulting in the disappearance of the low-temperature structural phase transition for isotopically mixed H-D crystals are examined.