Response of low quartz SiO₂ to the presence of an external static electric field: A density functional theory study

We present a systematic theoretical study of response properties of α -quartz SiO2 to an external static electric field in the framework of the density functional theory. The distortions of the electron density and crystalline structure by the application of the field are investigated and compared to x-ray scattering intensity variations obtained by Guillot when a macroscopic electric field of 28.8 kV/cm is applied along the crystallographic a axis. Our calculations show that the experimental macroscopic field produces mainly atomic displacements, with a negligible electronic contribution. The calculated displacements along the a axis are in good agreement with the experimental data obtained from structure factors while the perpendicular displacements are found to be smaller, as well as the rotations of the Si-O bonds in the two independent tetrahedra around the a axis. In this work, the direct gap, the high-frequency dielectric constant as well as the elastic and piezoelectric tensors are also computed in order to confirm the accuracy of our calculations.