Mg near the valence band maximum to Si 0 Mg near the conduction band minimum (i.e., a difference of 2 in the charge state) corresponds to populating the 2-electron antibonding a * 1 state residing in the band gap (Figure ). If E F is above the a * 1 state, then the state is filled and the Si Mg antisite defect has a neutral charge state; on the other hand, if E F is below the a * 1 state, then the state is unfilled and the Si +2 Mg charged defect forms. The transition in the charge state of the Mg Si antisite defect from +4 near the valence band maximum to -2 near the conduction band minimum (i.e., a difference of 6 in the charge state) is also explained by a filling of the 6-electron bonding t 1u states (Figure ). If E F is below the t 1u states, then the states are completely empty and devoid of 4 electrons, corresponding to the Mg +4 Si charged defect; on the other hand, if E F is above the t 1u states and near the conduction band minimum, then the states are completely filled and has 2 additional electrons, corresponding to the Mg -2