Spin Densities and Correlations in Regular Polyene Radicals

Abstract

Positive and negative ground-state spin densities are obtained exactly for regular Pariser-Parr-Pople radicals up to eleven carbons and Heisenberg antiferromagnetic chains up to fifteen spins. Molecular Pariser-Parr-Pople parameters for the ratio $|\frac{{\ensuremath{\rho}}_{\ensuremath{-}}}{{\ensuremath{\rho}}_{+}}|$ of total negative and positive spin densities extrapolate to \ensuremath{\sim} 0.43 for fifty sites, slightly above the ENDOR value for polyacetylene. Correlations in interacting Heisenberg systems lead to long-range interactions between spin solitons and a shifted midgap state.