Mechanical instability of α-quartz: A molecular dynamics study

Abstract

Pressure-induced amorphization in \ensuremath{\alpha}-quartz has been investigated using constant-pressure molecular-dynamics calculations with the two-body potential of van Beest, Kramer, and van Santen. Both the static properties and the crystalline-to-amorphous phase transition were very well reproduced. Through an analysis of the elastic moduli, the mechanism for the transformation is shown to be a mechanical instability driven mainly by a cooperative twisting and compression of the helical tetrahedral silicate units with an abrupt decrease in the ${\mathit{C}}_{12}$, ${\mathit{C}}_{23}$, ${\mathit{C}}_{13}$, ${\mathit{C}}_{14}$, and ${\mathit{C}}_{33}$ elastic moduli.