Localized hyperpolarizability approach to the origin of nonlinear optical properties inTeO2-based materials

Abstract

We present an ab initio molecular orbital theoretical approach to the origin of nonlinear optical (NLO) properties in the $\mathrm{Te}{\mathrm{O}}_{2}$-based materials from the viewpoint of ``electron pairs'' assigned to the individual chemical bond. Localized static dipole moments, linear polarizabilities, and hyperpolarizabilities of the individual chemical bonds in the $\mathrm{Te}{\mathrm{O}}_{4}$ and $\mathrm{Te}{\mathrm{O}}_{3}$ structural units are calculated in terms of the localized molecular orbitals. While no significant difference is found between these structural units in both the static bond dipole moment and the linear polarizability, the hyperpolarizabilities exhibit large differences. The $\mathrm{Te}{\mathrm{O}}_{4}$ structural unit shows much higher second hyperpolarizability than the $\mathrm{Te}{\mathrm{O}}_{3}$ structural unit. It is shown that the lone pair of the electrons on Te atom has the very large nonlinear response property, which should cause the high third-order NLO efficiency of the $\mathrm{Te}{\mathrm{O}}_{2}$-based materials. Geometric dependency of the second hyperpolarizability is also discussed on the basis of the calculations on the several deformed structural units.