Static polarizability and second hyperpolarizability of closed- and open-shell π-conjugated polymers.

The static longitudinal linear polarizability (α) and second order hyperpolarizability (γ) for neutral and charged, closed- and open-shell trans-polyacetylene (PA) chains C2nH2n+2, C2n-1H2n+1, C2n-1H2n+1+, C2nH2n+2+, and C2nH2n+22+ are systematically investigated and compared. The polarizabilities are calculated within the Pariser-Parr-Pople model, and the electron correlation effect is included through density matrix renormalization group. It turns out that for both α, and γ, two neutral PA chains C2nH2n+2 and C2n-1H2n+1 give similar values, while both singly charged and doubly charged systems present significantly larger magnitude of α and γ values than the two neutral chains. The two singly charged PA chains C2n-1H2n+1+ and C2nH2n+2+ give more apparent nonlinear optical responses than doubly charged case C2nH2n+22+ and both present negative second order hyperpolarizabilities for short to medium sized oligomers. The sign inversion of γ values in singly charged PA molecules is anticipated to take place at the much longer length than ever observed due to the significant effects of electron correlation and geometry. [ABSTRACT FROM AUTHOR]