Shell-model and first-principles calculations of vibrational, structural and ferroelectric properties of KH$_2$PO$_4$

TL;DR

This paper presents a shell model for potassium dihydrogen phosphate (KDP) fitted to ab initio results, accurately reproducing structural, vibrational, and ferroelectric properties, and successfully predicting phase transition behavior.

Contribution

The authors develop and validate a shell model for KDP based on ab initio data, enabling efficient simulations of its properties and phase transition.

Findings

Shell model accurately reproduces structural parameters.

Phonon spectra match experimental and ab initio data.

Phase transition temperature is predicted at approximately 360 K.

Abstract

We develop a shell model (SM) for potassium dihydrogen phosphate (KDP) which is fitted to ab initio (AI) results that include nonlocal van der Waals corrections. The SM is comprehensively tested by comparing results of structural, vibrational and ferroelectric properties with AI and experimental data. The relaxed structural parameters are in very good agreement with the AI results and the available experimental data. The $\Gamma$-point phonons and the total phonon densities of states (DOSs) in the ferroelectric and paraelectric phases calculated with the developed SM are in good overall agreement with the corresponding AI and experimental data. We also compute the effective Debye temperature as a function of $T$ which shows good accordance with the corresponding AI and experimental results. Classical molecular dynamics (MD) simulations obtained with the developed SM show a FE-PE phase transition at $\approx 360$ K in remarkable agreement with ab initio MD calculations.