Molecular mechanics study on the α-quartz/β-quartz transition

Abstract

Molecular mechanics calculations have been performed on the α/β-quartz phase transition. By applying a volume constraint the size of the unit cell of α-quartz was changed. At a transition volume V_tr= 0.1208 nm³ the symmetry of β-quartz was achieved. Calculated volume–pressure data are in agreement with experimental data. The negative pressure applied at the transition volume (–3.35 GPa) is in agreement with the experimental relation between pressure and transition temperature (dT_tr/dp). During the calculations the vibrational modes, the heat of formation and the structural parameters were followed as a function of the constrained volume. From a molecular mechanics point of view β-quartz is shown to be the stable structure at unit-cell volumes larger than V_tr.