THE HYPERPOLARIZABILITY OF TRANS-BUTADIENE REREVISITED

It has been stated that TDHF results for the dynamic second hyperpolar izability gamma(H) of trans-butadiene provide superior results to thos e obtained with electron correlation [P. Norman et al. J. Chem. Phys. 106, 1827 (1997)]. Using the newly developed correlated frequency depe ndent 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 and vibrational contributions, unlike TDHF, the EOM-CCSD method provides excellent agreement with experiment. The average gamma (H) at the experimental geometry in our best basis is 20.3 at omega=0. 043 a.u. and 28.0 at omega=0.0656 a.u. compared to experimental values of 20.2 +/-0.1 and 27.7 +/- 1.6, respectively. (C) 1998 American Inst itute of Physics.