Research On Electro-optic Tensor Of GaAs From Density Functional Perturbation Theory

In this paper, we introduce the density-functional theory (DFT) and the density-functional perturbation theory (DFPT) based on the 2n+1 theorem. The significance of the research on the electro-optic tensors of materials is proposed, and the decomposed expressions based on the DFPT of the electro-optic tensors are presented (according to the Born-oppenheimer approximation, the electro-optic tensor can be decomposed by the contribution of the ion and electron, respectively). To analyze the large electro-optic coefficients of the electro-optic materials, we select GaAs and c-BN that come from the III-V group. They have the same structure, but completely different electro-optic coefficients. The electro-optic tensors of GaAs and c-BN are calculated through the first-principles DFT. The absolute values of the electro-optic coefficients of GaAs are much higher than that of c-BN. By analyzing the composition of the electro-optic tensor, we find out that the contribution from electronics is the dominant factor. The results also indicate that the electro-optic tensor is according with the symmetry of the dot group. In addition, other relative features, such as the ground-state properties, piezoelectricity, lattice dynamics properties—phonon dispersion relation and Born effective charge are also obtained and analyzed.