Energetics and structure of Peierls-Hubbard chains in ground and excited states.

Abstract

The stationary states of a half-filled Peierls-Hubbard chain are calculated. To describe electron correlations, the wave functions as antisymmetrized products of strongly orthogonal geminals are used; wave functions and bond lengths are determined self-consistently by the variational method in an N=50 ring. The neutral soliton pair ${S}^{0}$${S}^{0}$ is obtained as corresponding to a local total-energy minimum above the perfectly dimerized ground state. The charged soliton pair ${S}^{+}$${S}^{\mathrm{\ensuremath{-}}}$ refers to the minimum in the subspace of wave functions which are odd with respect to charge conjugation. The creation energies for each of the pairs are estimated as functions of Hubbard parameter U and compared with the exact excitation energies of the uniform Hubbard chain. The electron correlation is shown to make the in-gap ${S}^{0}$${S}^{0}$ state stable even for a moderate electron-lattice coupling; the soliton width turns out to be much smaller than that in the U=0 model and comparable with the lattice constant. Applicability of the results to polyacetylene is discussed.