1ST-PRINCIPLES CALCULATION OF THE ELECTRONIC AND OPTICAL-PROPERTIES OF LINBO3

The electronic structure and optical properties of rhombohedral LiNbO3 have been studied by a first-principles method in the local-density approximation (LDA). An approximate k-dependent and energy-dependent self-energy-correction scheme is then applied to the LDA result, yielding a direct band gap of 3.56 eV at GAMMA. It is shown that the calculated dielectric function with the self-energy-corrected eigenvalues is in much better agreement with the optical and refractive index data than those from LDA. The calculated negative optical birefringence is in excellent agreement with experiment. Valence-charge analysis indicates the ionic formula for LiNbO3 to be Li0.98Nb3.67 (0-1.55)3.