title: Modeling of configurations and third-order nonlinear optical properties of methyl silsesquioxanes.
abstract: Configuration optimizations, excited state properties, and the frequency-dependent third-order nonlinear optical polarizabilities have been investigated on a series of methyl-silsesquioxane (MeT) cages [CH(3)SiO(1.5)](n) (n=4, 6, 8, and 10) using ab initio quantum mechanical methods coupled with the sum-over-states methods. The obtained electronic absorption spectra show a redshift as the cage size increases, and the absorption spectra are assigned as charge transfers from oxygen p type to silicon s type atomic orbitals. The calculated average third-order polarizabilities of <gamma> in the three optical physical processes (third-harmonic generation, the electric-field-induced second-harmonic generation, and degenerate four-wave mixing) have wide nonresonance regions. For all the considered species, the values of gamma decrease in the order of [MeT](4)>[MeT](8)(C(2v))=[MeT](10)>[MeT](6)>[MeT](8)(O(h)).
authors.affiliation: Fujian Institute of Research on the Structure of Matter, State Key Laboratory of Structural Chemistry, The Graduate School of the Chinese Academy of Sciences, Fuzhou, Fujian 350002, People's Republic of China.
authors.forename: J
authors.initials: J
authors.lastname: Shen
authors.forename: W-D
authors.initials: WD
authors.lastname: Cheng
authors.forename: D-S
authors.initials: DS
authors.lastname: Wu
authors.forename: X-D
authors.initials: XD
authors.lastname: Li
authors.forename: Y-Z
authors.initials: YZ
authors.lastname: Lan
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: Y-J
authors.initials: YJ
authors.lastname: Gong
authors.forename: F-F
authors.initials: FF
authors.lastname: Li
authors.forename: S-P
authors.initials: SP
authors.lastname: Huang