97-24U

An equation of Ornstein-Zernike type for ($q$, $\omega _n$)-dependent pair proton correlation functions of ferroelectrics and antiferroelectric of KH$_2$PO$_4$\ and NH$_4$H$_2$PO$_4$\ type crystals is derived in the mean field approximation in the longe-range interactions (the reference system) and the four-particle approximation in the short-range correlations. We take into account the tunneling effects; therefore, the model Hamiltonians contain non-commuting spin operators. Deuterated crystals are also considered, for which expressions for dielectric susceptibilities are found.