Effects of Native Vacancies on Nb-Doped MgH2 Using Density Functional Theory Calculations

In the present work, we considered the effect of Nb and charged vacancies on the properties of magnesium hydride. We performed spin-polarized ab initio calculations substituting an Mg atom by an Nb impurity. Then, some charged vacancies were included in the MgH2 + Nb system (VH, VMg, or VMg–H). In each case, three possible charge states were considered (+1, 0, or −1). We computed cohesion and formation energies, band gap, and magnetic moment. We also calculated the transition level energy value and the density of states. Nb states are located in the gap, and a magnetic moment is induced. In the case of the system with charged vacancies, we found that VH+ and VH0 are the more probable vacancies formed, and the states near the Fermi level (EF) are filled, thus getting an important reduction in the band gap.