Chemical Trend of Pressure-Induced Metallization in Alkaline Earth Hydrides

The pressure-induced metallization of alkaline earth hydrides was systematically investigated using ab initio methods. While BeH2 and MgH2 present different semimetallic phases, CaH2, SrH2, and BaH2 share the same metallic phase (P6/mmm). The metallization pressure shows an attractive decrease with each increment of metal radius, and this trend is well correlated with both the electronegativity of alkaline earth metals and the band gap of alkaline earth hydrides at ambient pressure. Our results are consistent with current experimental data, and the obtained trend has significant implications for designing and engineering metallic hydrides for energy applications.