Post-stishovite transition in AlOOH-incorporated SiO2

In 2007, Lakshtanov et al. [Proc. Nat. Acad. Sci. 104, 13588 (2007)] showed that the incorporation of AlOOH into SiO$_{2}$ significantly reduces the transition pressure between stishovite and CaCl$_{2}$-type phases. In the present paper, we investigate theoretically the effect of hydrogen and aluminum on this transition. First-principles calculations show that aluminum has no effect on the transition pressure. However, hydrogen bonds play a crucial role, suggesting that a cooperative redistribution of hydrogens aids the post-stishovite transition. Large-scale molecular dynamics simulations using model potentials confirm this effect and reveal the nature of the hydrogen motion. This effect produces a strong temperature dependence on the transition pressure and should make the latter sensitive to hydrogen content in the material.