THE PARISER-PARR-POPLE MODEL FOR TRANS-POLYENES .2. PARAMETRIZATION AND GROUND-STATE DYNAMICS

The parameter space of the Pariser-Parr-Pople model was surveyed to fit the bond alternation potential of trans-butadiene obtained by ab initio Hartree-Fock and correlation calculations. Since no unique best fit parameter set could be found, ab initio Hartree-Fock geometry optimization results on (C21H23)+, C22H24 and (C22H24)2+ found in the literature were taken as additional data. We found as resonance integral beta-0 = -2.4 eV and as on-site Coulomb repulsion parameter gamma-0 = 11.25 eV as optimum values in agreement with usually used values for these parameters. The electron-phonon coupling constant is found to be alpha = 1.9 eV/angstrom much smaller than the Su-Schrieffer-Heeger value for alpha. Ground state soliton dynamics are presented and it is shown that dynamical properties are verv sensitive to the parametrization. At the optimum parameter set, moving solitons exist in the system. From a dimerization potential we obtain a force constant which agrees with experiment.