title: Open-shell ground state of polyacenes: a valence bond study.
abstract: Applying the density matrix renormalization group (DRMG) method to a nonempirical valence bond (VB) model Hamiltonian, we studied polyacene oligomers of different lengths in the strong electron correlation limit. Geometrical optimizations were performed for the lowest singlet and triplet states of oligomers up to [40]-acene, and a convergence of the bond lengths toward the polymer limit is observed in the interior of the oligomer. For large oligomers, as well as for the polymer, the ground state can be reasonably determined to be a singlet. Furthermore, a high similarity between the singlet geometries and triplet geometries suggests an open-shell character for the singlet ground state. A reasonable speculation of the soliton-antisoliton pair character of the singlet ground state was supported by a spin distribution analysis of the triplet state wave function of large oligomers, with each of the two solitons being broadly delocalized over the upper or bottom edge of the oligomers, respectively.
authors.affiliation: Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of the Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210093, China.
authors.forename: Zexing
authors.initials: Z
authors.lastname: Qu
authors.forename: Dawei
authors.initials: D
authors.lastname: Zhang
authors.forename: Chungen
authors.initials: C
authors.lastname: Liu
authors.forename: Yuansheng
authors.initials: Y
authors.lastname: Jiang