The atomic orbitals of the Mg on Si antisite defect (Mg Si ) interact with the Mg 8 molecular orbitals surrounding the Si site, for which the energies are the same as those for V Si (Figures ). Since a Mg atom occupies a Si site in Mg Si , the atomic orbital energies of the Mg atom will be shifted downwards due to the Madelung potential, which is attractive for electrons at an an- The density of states of Mg 2 Si, with a Mg Si defect included, exhibits a set of peaks which is partially Mg Si -p character (d). These peaks correspond to the bonding t 1u states, since the peaks can hold up to 6 electrons total as they are completely filled when 2 electrons are added to the system (Mg -2 Si ) and empty when 4 electrons are taken away (Mg +4 Si ). The charge density distribution, which is calculated from states within the highlighted energy window for Mg 0