Ab initio molecular orbital calculation of the second hyperpolarizability of the carbon disulfide molecule: electron correlation and frequency dispersion

The second hyperpolarizability (γ) of the carbon disulfide molecule is calculated by the ab initio molecular orbital method considering basis set dependence, electron correlation and frequency dispersion. The quality of the basis set is found to influence strongly the correlation correction. The 6-31G basis set augmented with diffuse p and d functions (6-31G + pd overestimates the correlation effect on the second hyperpolarizability. The 6-31G + pdd basis set, made by augmenting the 6-31G + pd basis set with one more semi-diffuse d function, gives γ values similar to those with a more accurate 6-31G(3d) + pd basis set at both the Hartree-Fock and correlated levels.