Orbital population and topology of Mg dihydride

Abstract

Resorting to ab initio methods to theoretically study the properties of materials provides a suitable avenue to delve into spaces not accessible to experimental techniques. Their benefits hinge on the precise selection of the electron charge density, which, together with a suitable Hamiltonian representing the system, provides access to each property of interest in the material. Using CRYSTAL17 software and polarization-quality double and triple zeta valence Gaussian basis sets, we performed an extensive study of the properties of Mg dihydride in its α and β structural states at zero pressure, highlighting that both hydrides are elastically stable and ductile, α-MgH2 exhibiting a semiconducting behavior and β-MgH2 showing a conducting character. The study of the orbital population revealed an Mg-H and Mg-Mg bonding state and an H-H anti-bonding one, the integrated population, ICOOP, showing a higher order bond in the cubic than in the tetragonal structure; and ICOHP exhibiting the β-MgH2 hydride as more unstable than α-MgH2. The charge density topology reflected Mg-H and H-H bond lengths little affected by the basis sets used, while their Laplacian topology revealed a region of charge concentration around Mg and a region of depletion around hydrogen and other critical points encountered, further revealing the ionic-covalente transition bond character for both structures.