First-Principles Determination of the Structure of Magnesium Borohydride

TL;DR

This study uses ab initio calculations to predict new stable structures of magnesium borohydride under pressure, aligning well with experimental data and advancing understanding of its phase behavior.

Contribution

The paper introduces two new low-enthalpy tetragonal structures of Mg(BH4)2 predicted by evolutionary calculations, supported by simulated XRD and EOS data.

Findings

Identified two new stable tetragonal phases of Mg(BH4)2.

Predicted structures match experimental XRD patterns.

Quantified properties like density and bulk modulus.

Abstract

The energy landscape of Mg(BH4)2 under pressure is explored by ab initio evolutionary calculations. Two new tetragonal structures, with space groups P-4 and I41/acd are predicted to be lower in enthalpy, by 15.4 kJ/mol and 21.2 kJ/mol, respectively, than the earlier proposed P42nm phase. We have simulated X-ray diffraction (XRD) spectra, lattice dynamics, and equations of state (EOS) of these phases. The density, volume contraction, bulk modulus, and the simulated XRD patterns of I41/acd and P-4 structures are in excellent agreement with the experimental results.