Thursday, November 29, 2012

1211.6521 (Qiang Zhu et al.)

Unexpected Stoichiometries in Mg-O System under High Pressure    [PDF]

Qiang Zhu, Artem R. Oganov, Andriy O. Lyakhov
Using ab initio evolutionary simulations, we explore all the possible stoichiometries for Mg-O system at pressures up to 850 GPa. In addition to MgO, our calculations find that two extraordinary compounds MgO$_2$ and Mg$_3$O$_2$ become thermodynamically stable at 116 GPa and 500 GPa, respectively. Detailed chemical bonding analysis shows large charge transfer in all magnesium oxides. MgO$_2$ contains peroxide ions [O-O]$^{2-}$, while non-nuclear electron density maxima play the role of anions in the electride compound Mg$_3$O$_2$. The latter compound is calculated to have a much narrower band gap compared to MgO and MgO$_2$. We discuss conditions at which MgO$_2$ and Mg$_3$O$_2$ might exist in planetary conditions.
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