01-10U

Within the proton ordering model with taking into account the short-range interaction and proton tunneling in the cluster approximation, and long-range interactions in the mean field approximation, we study the thermodynamic and static dielectric properties of the KH$_2$PO$_4$\ type ferroelectrics. We show that under the proper choice of the theory parameters for the crystals KH$_2$PO$_4$, RbH$_2$PO$_4$, KH$_2$AsO$_4$, RbH$_2$AsO$_4$\, a good quantitative agreement of the theoretical results with the corresponding exparimental data for the temperature dependence of spontaneous polarization, specific heat, longitudinal and transverse static dielectric permittivities, as well for the Curie-Weiss temperature and constant takes place. We study a change of character of the nonphysical behavior of the cluster approximation depending on the tunneling value.