Density functional energetics of alpha-quartz for calibration of SiO2 interatomic potentials

All-electron, Gaussian basis density functional theory (DFT) total energies for alpha-quartz were generated on a substantial grid of points for eventual use in a first-principles check of calibration of a widely used effective interionic potential for SiO2. Unlike a previous all-electron, Gaussian basis calculation, we do not find a weak double minimum with respect to cell volume. Rather there is a weak double minimum with respect to internal cell parameters that is at the margins of numerical precision and, hence, may only be the signal of a very flat potential surface. The results show typical dependence on the choice of approximate DFT functional and differ from experimental values enough that both aspects may be problematic for parametrization of potentials.