Quantum Effects in Hydrogen-Bonded Ferroelectrics

The isotope effect and the quantum saturation effect in hydrogen-bonded ferroelectrics, such as KH2PO4 (KDP), are studied by using a simple coupled dipole-proton model under two opposite adiabatic approximations. The model of interacting tunneling protons and the model of interacting dipoles, as two traditional models for KDP, are reproduced from this study and results of the latter model correspond better to experimental findings in KDP. Therefore, the modified strong dipole-proton coupling model, as a more realistic model of interacting dipoles for KDP, and the path-integral Monte Carlo method are applied to estimate the quantum saturation effect in KDP.