Exploring the Landscape of MgO Polymorphs: Stability and the Electronic Band Gap of Promising Candidates

Magnesium oxide (MgO) is one of the most scientifically important minerals and materials, since it is chemically simple yet extremely stable, with many applications ranging from building materials, textiles, pharmaceuticals, and environmental applications, to catalysis, spintronics, and opto‐electronic applications. In addition to the experimentally observed rock salt structure as the global minimum on the energy landscape of MgO, a diverse set of local minima exist, exhibiting the CsCl, wurtzite, sphalerite, NiAs, anti‐NiAs, and 5–5 structure type, as well as the TiP, 4H, and 9R polytype structures, where their thermodynamic stabilities were evaluated through total energy and phonon calculations on an ab initio level. The electronic properties and the band gap were computed for each of the predicted MgO polymorphs using three different ab initio methods, and it was shown that the band gap nicely correlates with the Mg–O nearest neighbor distances in the modifications. This study shows the structural richness of MgO, which is reflected in, e.g., recent thin film experiments, and demonstrates its potential for tuning the band gap of MgO by employing different polymorphs.