MECHANICAL INSTABILITY OF ALPHA-QUARTZ - A MOLECULAR-DYNAMICS STUDY

Pressure-induced amorphization in a-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 tetrahedal silicate units with an abrupt decrease in the C-12, C23, C-13, C-14, and C33 elastic moduli.