High pressure investigations on Hydrous Magnesium Silicate-Phase A using first principles calculations, H--H repulsion and O-H bond compression

TL;DR

This study uses first principles calculations to investigate the structural behavior of hydrous magnesium silicate Phase A under high pressure, revealing no phase transition up to 45 GPa and a unique H--H repulsion mechanism involving O-H bond reduction.

Contribution

It provides the first detailed computational analysis of Phase A's high-pressure behavior, highlighting a novel H--H repulsion mechanism distinct from previous models.

Findings

No phase transition up to ~45 GPa.

H--H distance limits at 1.85 Å.

Unique O-H bond reduction mechanism.

Abstract

We have carried out first principles structural relaxation calculations on the hydrous magnesium silicate Phase A (Mg7Si2O8(OH)6) under high pressures. Our results show that phase A does not undergo any phase transition upto ~ 45 GPa. We find that non-bonded H--H distance reaches a limiting value of 1.85 angstrom at about 45 GPa. The H--H repulsive strain releasing mechanism in Phase A is found to be dramatically different from the hydrogen bond bending one that was proposed by Hofmeister et al1 for Phase B. It is based on the reduction of one of the O-H bond distances with compression.