Molecular and lattice dynamical study on modulated structures in quartz

It is shown that atomistic simulations using the Tsuneyuki potential for silica (SiO2) correctly reproduce the major experimentally observed properties of the incommensurate (INC) phases in quartz, such as the phase sequence, the direction of the modulation, the coupling of the soft optic with the TA modes, the dispersion surface anisotropy, the stress dependence of the transition temperature, etc. The obtained phase diagram is topologically equivalent to those predicted from general INC phase theories. At high temperature, our results give a short period modulation with kapproximate tob/3 as predicted by the new model for the origin of INC phase in quartz [Aslanyan , J. Phys.; Condens. Matter 10, 4565 (1998); 10, 4577 (1998)].