Density Functional Theory Predictions of the Nonlinear Optical Properties in α-Quartz-type Germanium Dioxide

We calculated the lattice dynamics, the second-order nonlinear susceptibility, and the electro-optic response of the germanium dioxide in its alpha-quartz-type form (alpha-GeO2) from first-principles calculations based on density functional theory. No theoretical or experimental investigations of these nonlinear optical properties have been previously reported in the literature. The calculation of the infrared and Raman spectra of alpha-GeO2 allowed us to assign its experimental phonon modes, contributing to the clarification of a long-standing debate in the literature. The second-order nonlinear susceptibility and the electro-optic coefficients of alpha-GeO2 are predicted to be significantly higher than those reported for alpha-quartz. Thus, alpha-GeO2 should be a promissing candidate for nonlinear optical applications when compared to alpha-quartz.