## Abstract

The frequency-dependent electronic second hyperpolarizability of increasingly large polysilane chains is computed for the most common nonlinear optical (NLO) processes at the time-dependent Hartree-Fock level with the 6-31G atomic basis set. Due to σ-conjugation, the longitudinal component (γ_{L}
^{e}) turns out to be dominant. Its nonresonant dispersion relations are described by the coefficients of the power expansion formula, γ_{L}
^{e}[(-ω_{σ}; ω_{a}, ω_{2}, ω_{3}) = γ_{L}
^{e}(0; 0, 0, 0)[1 + Aω_{L}
^{2} + Bω_{L}
^{4} + Cω_{L}
^{6} + ⋯], where ω_{L}
^{2} = ω_{σ}
^{2} + ω_{1}
^{2} + ω_{2}
^{2} + ω_{3}
^{2} and γ_{L}
^{e}(0; 0, 0, 0) is the static limit value. In the infinite chain length limit, the CHF/6-31G static longitudinal electronic second hyperpolarizability per Si_{2}H_{4} unit cell is estimated to attain 463 ± 10 × 10^{3} a.u. whereas the A coefficient reaches 27.8 ± 0.9 a.u. The accuracy that could be reached from using this power expansion expression for estimating the second hyperpolarizability for other optical frequencies is discussed.

Original language | English |
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Pages (from-to) | 737-743 |

Number of pages | 7 |

Journal | International Journal of Quantum Chemistry |

Volume | 70 |

Issue number | 4-5 |

Publication status | Published - 1 Dec 1998 |

## Keywords

- Electronic second hyperpolarizability
- Frequency dispersion
- Polysilane