Pressure effects on soft-mode dynamics in KDP-type ferroelectrics

Molecular dynamics simulation and the modified strong dipole-proton coupling (MSDPC) model are used to show how the soft mode of ferroelectric phase transition in KH2PO4 (KDP) changes its spectral shape at room temperature due to the decrease in the hydrogen-bond length. The effect of hydrogen-bond shortening, which simulates the effect of pressure increase in experiment, appears as the strong decrease in the soft-mode damping accompanied with the weak increase in the soft-mode frequency. These results are in accordance with the experimentally detected effect of pressure increase on the soft-mode Raman scattering spectra.