Hyperpolarizabilities of molecules with frequency dependence and electron correlation

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Abstract
Frequency dependent second hyperpolarizabilities of N2 and the prototype organic molecule trans‐butadiene are reported using generalized time dependent Hartree–Fock (TDHF) theory for several frequencies of applied fields. A monotonic increase of the values (positive dispersion) is observed for every nonlinear optical process in a range of frequencies for the applied field. Correlation effects are estimated using a second‐order many body perturbation theory and coupled cluster singles and doubles relaxed density method for the analytical determination of the induced dipole moment. Such hybrid results for DC‐induced second harmonic generation provide reasonable values in comparison with experiment for N2. However, dispersion and correlation effects in trans‐butadiene are both found to be large and could be nonadditive.