Models for the amorphization of compressed crystals

A permanently bonded diamond network, with flexible bond lengths and angles, is characterized by computer simulation and used as the reference state for a perturbation treatment that favours tetrahedral bond angles. At low temperatures the perturbed system has three phases separated by two sets of van der Waals loops. The intermediate-pressure phase is an open crystal which, like ice or quartz, expands when cooled and collapses under pressure to an amorphous solid. Two-dimensional honeycomb networks show the same behaviour.