AB-INITIO LONGITUDINAL POLARIZABILITIES OF CONJUGATED STEREOREGULAR POLYMERS WITH A CARBON BACKBONE

Ab initio coupled (random phase approximation) and uncoupled (sum over states) Hartree-Fock calculations of the asymptotic longitudinal pola rizabilities are carried out for conjugated infinite periodic systems with a carbon backbone: polyacetylene, polyyne, polydiacetylene, and p olybutatriene. Direct polymeric methods are employed and compared to v alues extrapolated from finite oligomeric longitudinal polarizability calculations and to available experimental values. For polybutatriene where finite oligomeric calculations failed to give the asymptotic val ue, we estimate the asymptotic longitudinal polarizabilities per unit length to be 19.3 and 68.4 atomic units in the minimal STO-3G atomic b asis at the uncoupled and coupled Hartree-Fock levels, respectively.