Electronic correlations and midgap absorption in polyacetylene

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Abstract
Electronic correlations are important when they lift degeneracies of Huckel models. Standard Pariser–Parr–Pople (PPP) parameters split the degenerate midgap absorption of neutral solitons in undoped trans polyacetylene (CH)x. The dipole intensity goes entirely to the upper state close to the optical gap Eg. PPP correlations lower slightly the nondegenerate transition at Eg/2 of charged solitons, which consequently provide all the E∼Eg/2 intensity. Exact symmetries of correlated states and finite‐chain computations are exploited in associating the midgap absorption of neat and lightly doped (CH)x entirely with charged solitons.

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