Equation-of-Motion Calculations on an Isolated Chain of Polyacetylene

Abstract

Abstract An equation-of-motion (EOM) method for calculating the excited states of one-dimensional systems is discussed. This method is similar to configuration-interaction theory except the ground state is constrained to remain the Hartree-Fock ground state. Issues relating to the size-consistency of the method are briefly discussed. EOM calculations are performed using the semi-empirical Hamiltonian appropriate for gas-phase polyenes. In these calculations, electrons and holes are created on the Hartree-Fock ground state. In the low energy states, the electrons and holes get bound together by Coulomb forces into many-body excitations, or effective particles. These effective particles are delocalized over the entire polymer, but there is limited separation between the electrons and holes within the particle. The effective particles may have significant contributions from both single and double electron-hole pair configurations. It is speculated that dielectric screening may be much weaker for states with ...