EQUATION-OF-MOTION CALCULATIONS ON AN ISOLATED CHAIN OF POLYACETYLENE

An equation-of-motion (EOM) method for calculating the excited states of one-dimensional systems is discussed. This method is similar to con figuration-interaction theory except the ground state is constrained t o remain the Hartree-Fock ground state. Issues relating to the size-co nsistency of the method are briefly discussed. EOM calculations are pe rformed using the semi-empirical Hamiltonian appropriate for gas-phase polyenes. In these calculations, electrons and holes are created on t he Hartree-Fock ground state. In the low energy states, the electrons and holes get bound together by Coulomb forces into many-body excitati ons, 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 h ave significant contributions from both single and double electron-hol e pair configurations. It is speculated that dielectric screening may be much weaker for states with small electron-hole pair separations th an for states with large electron-hole pair separations. The effective particles present in the low-energy highly-correlated states may then remain essentially intact; while at the same time, dielectric screeni ng may significantly lower the energy of the free electron-hole pair, charge-separated states.