Investigation of structure and hydrogen bonding of superhydrous phase B (HT) under pressure using first-principles density functional calculations

Abstract

High-pressure behaviour of superhydrous phase B (high temperature; HT) of Mg₁₀Si₃O₁₄(OH)₄ (Shy B) is investigated with the help of density functional theory-based first-principles calculations. In addition to the lattice parameters and equation of state, we use these calculations to determine the positional parameters of atoms as a function of pressure. Our results show that the compression induced structural changes involve cooperative distortions in the full geometry of the hydrogen bonds. The bond-bending mechanism proposed by Hofmeister et al. (Vibrational spectra of dense hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle, Am. Miner. 84 (1999), pp. 454–464) for hydrogen bonds to relieve the heightened repulsion due to short H- - -H contacts is not found to be effective in Shy B. The calculated O–H bond contraction is consistent with the observed blue shift in the stretching frequency of the hydrogen bond. These results establish that one can use first-principles calculations to obtain reliable insights into the pressure-induced bonding changes of complex minerals.

Keywords:

• DFT calculations
• superhydrous Phase B
• hydrogen bonding