Structure and elastic properties of Mg(OH)$_2$ from density functional theory

TL;DR

This study uses density functional theory and molecular dynamics to analyze the structure, lattice dynamics, and elastic properties of Mg(OH)$_2$, revealing hydrogen atom disorder and angular correlations up to 150 K.

Contribution

It provides new insights into the disordered hydrogen subsystem and its correlations in Mg(OH)$_2$, supported by computational modeling and comparison with experimental data.

Findings

Elastic constants agree with experimental data

Hydrogen atoms show disordered behavior with angular correlations

Rotational degrees of freedom decouple from lattice above 30 K

Abstract

The structure, lattice dynamics and mechanical properties of the magnesium hydroxide have been investigated with static density functional theory calculations as well as \it {ab initio} molecular dynamics. The hypothesis of a superstructure existing in the lattice formed by the hydrogen atoms has been tested. The elastic constants of the material have been calculated with static deformations approach and are in fair agreement with the experimental data. The hydrogen subsystem structure exhibits signs of disordered behaviour while maintaining correlations between angular positions of neighbouring atoms. We establish that the essential angular correlations between hydrogen positions are maintained to the temperature of at least 150 K and show that they are well described by a physically motivated probabilistic model. The rotational degree of freedom appears to be decoupled from the lattice directions above 30K.