LATTICE-DYNAMICS OF A PAIR-POTENTIAL MODEL OF ALPHA-QUARTZ

A pair potential for SiO2 proposed by Tsuneyuki, Tsukada, Aoki, and Matsui [Phys. Rev. Lett. 61, 869 (1988)] is used to calculate a range of lattice dynamical properties of alpha-quartz. The potential energy of the structure is minimized, and the phonon frequencies are calculated for the structural parameters corresponding to the energy minimum. Frequencies calculated throughout the Brillouin zone are used to construct a frequency distribution function and the harmonic contributions to the thermodynamic functions are calculated. The coefficients of thermal expansion perpendicular and parallel to the c axis are calculated in a perturbative approximation. The expansion coefficient parallel to the c axis is found to be negative at low temperatures, in agreement with experiment. The elastic, dielectric, and piezoelectric constants are also calculated.