POLARIZABILITY CALCULATIONS WITH THE SCF METHOD .3. ETHYLENE, BUTADIENE, AND HEXATRIENE

We evaluate the nonlinear third-order electric susceptibilities of ethylene, trans-butadiene, and trans-hexatriene by combining the Pariser-Parr-Pople method and the extended Hückel method. It follows from the nature of the calculations that the theoretical results are quite sensitive to approximations since the final results are obtained from various positive and negative contributions. If we allow for a possible 10% error in each contribution, then our result and the corresponding error margins are γ=-0.03±0.03 for ethylene, γ=1.35±0.75 for trans-butadiene, and γ=9.92±5 for trans-hexatriene, all values are expressed in terms of 10-36 esu. We feel that these values are consistent with experimental results obtained by Ward and Elliott. © 1980 American Institute of Physics.