Ab initio polarizabilities of polyenic chains with conformational defects

We present an ab initio Hartree-Fock study of the electronic polarizabilities of the C2n+1H2n+3+ (2 < n < 11) and C2nH2n+2++ (2 < n < 15) oligomers of polyacetylene. After a complete geometry optimization implemented through the GAUSSIAN 92 program, the longitudinal components of the linear polarizabilities were analytically determined and the second hyperpolarizabilities calculated through a finite field procedure. While the first hyperpolarizabilities of the bipolaron-like structures vanish (since inversion symmetry is preserved), the dominant component beta(xxy) of the soliton chains was obtained analytically. We confirm that the polarizabilities of these polyenic oligomers are quite sensitive to the nature of the conformational defect present.