ion site (Figure ). The s-and p-orbitals of the Mg atom will interact with the a 1g and t 1u states of Mg 8 , respectively, forming the same molecular orbitals as those for an interstitial defect (Figure ). Since there are 4 electrons from the Mg 8 complex and 2 valence electrons from the Mg atom, there are 6 electrons that fill the molecular orbitals of Mg 0 Si , which results in partially-filled bonding t 1u states (Figure ).