Vibronic States of Polyacetylene, (CH)x

Electronic states of π-electrons coupled with lattice vibrations in a linear conjugated carbon chain, are calculated with a particular purpose of clarifiing the vibronic structure of bond alternation defect. First the vibronic Hamiltonian is derived from a general Hamiltonian. It is shown in the adiabatic approximation that the ground state of an odd number of carbon atoms corresponds to the bond alternation defect with an unpaired electron. Then taking account of the kinetic energy of lattice vibrations, the vibronic states of the defect is obtained. It is shown that the unpaired electron moves relatively freely. Finally a method to calculate self-consistently the electronic states and the lattice deformation in the presence of Coulomb interaction is presented. It is shown within the Hartree-Fock approximation that the ground state changes from CDW state to SDW state with increase of on-site Coulomb interaction.