Periodic pseudopotential Hartree–Fock study of α-quartz structure SiO2 and GeO2

Periodic pseudopotential Hartree–Fock calculations have been performed on the quartz structure of silica and germanium dioxide. It is shown that the tilt angle is the most important structural parameter. This parameter emphasizes the role of the oxygen polarization function which appear to be necessary to recover the correct geometry of low quartz. The structure of β-quartz is rationalized on the basis of the energy dependence upon the tilt angle and the absence of β-structure in GeO2 is explained. Finally the behavior of both oxides under pressure is discussed.