Electron correlation and structure dependencies of the second hyperpolarizability of ethylene

Abstract

We investigated an interesting behavior in electron correlation and Ž . structure dependencies of the second hyperpolarizability g of the ethylene model. The g values of the ethylene model with plain and twisted structures were examined using various ab initio MO methods. g was found to be largely changed depending on the rotation angle of the CH group in ethylene. The rotation-angle dependence of g is 2 remarkably different among Hartree]Fock and higher-order electron-correlation results. By applying hyperpolarizability density analysis, it was found that there are negative and positive contributions to g and that, especially, s electrons play an important role to determine the rotation-angle dependence of g at high-order electron correlation levels. Q 1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 177]183, 1999