Simulation of Modulated Structures in Quartz

Abstract

We report the results of molecular-dynamics calculation of equilibrium modulated phases of quartz in the vicinity of pressure induced α -β transition. A numerical method suitable for simulation of modulated phases in the vicinity of transition point was developed. The phase diagram with respect to the unit cell deformations was obtained from the pairwise interatomic potentials by [Tsuneyuki et al.: Phys. Rev. Lett. 61 (1988) 869]. The results show that the modulated structures with various wavevectors appear between α- and β-phases suggesting that the softening may occur at any point on the Σ line in the Brillouin zone and that a structure with large wavevector seems to be more probable than one with a small wavevector.