It has been stated that TDHF results for the dynamic second hyperpolarizability ␥ ʈ of trans-butadiene provide superior results to those obtained with electron correlation ͓P. Norman et al. J. Chem. Phys. 106, 1827 ͑1997͔͒. Using the newly developed correlated frequency dependent EOM-CCSD method we critically address this question. Using three geometries and three basis sets to assess the importance of the right choice of these parameters, and estimating orbital relaxation, triple excitations

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... d vibrational contributions, unlike TDHF, the EOM-CCSD method provides excellent agreement with experiment. The average ␥ ʈ at the experimental geometry in our best basis is 20.3 at ϭ0.043 a.u. and 28.0 at ϭ0.0656 a.u. compared to experimental values of 20.2 Ϯ0.1 and 27.7Ϯ1.6, respectively.