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Issue 26, 2018
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Anharmonic contribution to the stabilization of Mg(OH)2 from first principles

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Abstract

Geometrical and vibrational characterization of magnesium hydroxide was performed using density functional theory. Four possible crystal symmetries were explored: P[3 with combining macron] (No. 147, point group −3), C2/m (No. 12, point group 2), P3m1 (No. 156, point group 3m) and P[3 with combining macron]m1 (No. 164, point group −3m) which are the currently accepted geometries found in the literature. While a lot of work has been performed on Mg(OH)2, in particular for the P[3 with combining macron]m1 phase, there is still a debate on the observed ground state crystal structure and the anharmonic effects of the OH vibrations on the stabilization of the crystal structure. In particular, the stable positions of hydrogen are not yet defined precisely, which have implications in the crystal symmetry, the vibrational excitations, and the thermal stability. Previous work has assigned the P[3 with combining macron]m1 polymorph as the low energy phase, but it has also proposed that hydrogens are disordered and they could move from their symmetric position in the P[3 with combining macron]m1 structure towards P[3 with combining macron]. In this paper, we examine the stability of the proposed phases by using different descriptors. We compare the XRD patterns with reported experimental results, and a fair agreement is found. While harmonic vibrational analysis shows that most phases have imaginary modes at 0 K, anharmonic vibrational analysis indicates that at room temperature only the C2/m phase is stabilized, whereas at higher temperatures, other phases become thermally competitive.

Graphical abstract: Anharmonic contribution to the stabilization of Mg(OH)2 from first principles

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Publication details

The article was received on 18 Apr 2018, accepted on 01 Jun 2018 and first published on 05 Jun 2018


Article type: Paper
DOI: 10.1039/C8CP02490A
Citation: Phys. Chem. Chem. Phys., 2018,20, 17799-17808
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    Anharmonic contribution to the stabilization of Mg(OH)2 from first principles

    P. Treviño, A. C. Garcia-Castro, S. López-Moreno, A. Bautista-Hernández, E. Bobocioiu, B. Reynard, R. Caracas and A. H. Romero, Phys. Chem. Chem. Phys., 2018, 20, 17799
    DOI: 10.1039/C8CP02490A

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