Resistivity mechanisms in phthalocyanine-based linear-chain and polymeric conductors: Variation of bandwidth with geometry

The Wolfsberg-Helmholtz correlation between overlap and exchange integrals has been employed along with a tight-binding band scheme to study the effects of various geometric distortions on the calculated bandwidths of the phthalocyanine-based polymeric conductor [Si(Pc)O]_n (Pc = phthalocyaninato). Importantly, the Wolfsberg-Helmholtz parameterization constant has been calculated for the overlapping, cofacial π systems in a dimeric fragment of the polymer by using coulomb and exchange integrals and molecular wave functions derived from an all-electron ab initio DVM-Xα calculation on the monomeric phthalocyanine subunit. The results indicate that bandwidths calculated by using a simple Wolfsberg-Helmholtz type correlation with properly calculated parameters are in remarkably good agreement with those calculated from DVM-Xα. Consequently, the determination of phonon- and libron-induced modulations of polymeric bandwidths in such conductors requires high-level electronic structure calculations only for the monomeric subunits. The phthalocyanine motions parallel to the Si-O-Si backbone and the rotations about this backbone appear to dominate the resistivity, since their electron/vibration coupling constants are large.