Static polarizability of interactingπelectrons in conjugated polymers

The static polarizability per site, {α}(0)/N, of interacting {π} electrons is found exactly for N{≤}12 sites. The Pariser-Parr-Pople (PPP) model for trans-polyenes extrapolates to a polyacetylene (PA) polarizability of 7.4 A³ along the chain, more than an order of magnitude lower than for noninteracting electrons. Coulomb interactions in systems with electron-hole symmetry and a finite optical gap Eg are shown in general to decrease {α}(0)/N, by means of a bound that depends only on ground-state charge correlation functions. We also obtain the transverse polarizability of trans-polyenes of arbitrary length in one-electron theory, where the H\"uckel and Hartree-Fock {π} orbitals are closely related. The enhanced {π}-electron polarizabilities of finite polyenes and of soluble polydiacetylenic polymers are both consistent with PPP results using the identical microscopic parameters.