First Principles Calculation of SiO2 at High Pressures

Total energy of SiO2 as a function of unit cell volume has been calculated for -quartz, rutile and CaCl2 structures using the density function theory (DFT) and Hartree-Fork (HF) method. According to the Murnaghan's equation of state, the bulk modulus B0 and B=dB/dp for these three structures have been obtained. The calculated results are all in good agreement with experimental and other theoretical data available in the literature, which indicate that SiO2 will transform from -quartz structure to CaCl2 structure as pressure increasing, and there is no phase transition between rutile structure and CaCl2 structure, namely they can coexist. By analyzing the changes of the lattice parameters, the electronic density of states, and the band gap under pressure, it is found that in -quartz SiO2 the energy band width and charge transfer increase with increasing pressure. Moreover, the Si─O bond length is shortened and the electric charges are redistributed.