Ferroelectricity and isotope effects in hydrogen-bonded KDP crystals

TL;DR

This study uses first principles calculations to explore how nuclear quantum effects and deuteration influence ferroelectricity and structure in hydrogen-bonded KDP crystals, revealing the microscopic origin of isotope effects.

Contribution

It provides a detailed quantum mechanical analysis of isotope effects in KDP, linking proton probability depletion to lattice expansion and ferroelectric behavior.

Findings

Deuteration reduces proton density at the O-H-O bridge center.

Lattice expansion couples with proton off-centering, affecting ferroelectricity.

The study explains the giant isotope effect through quantum and geometrical interactions.

Abstract

Based on an accurate first principles description of the energetics in H-bonded KDP, we conduct a first study of nuclear quantum effects and of the changes brought about by deuteration. Cluster tunneling involving also heavy ions is allowed, the main effect of deuteration being a depletion of the proton probability density at the O-H-O bridge center, which in turn weakens its proton-mediated covalent bonding. The ensuing lattice expansion couples selfconsistently with the proton off-centering, thus explaining both the giant isotope effect, and its close connection with geometrical effects.