EFFECTIVE-HAMILTONIANS OF POLYMETHINEIMINE, POLYAZINE AND POLYAZOETHENE - A DENSITY-MATRIX VARIATION APPROACH

A new variation method is proposed to determine the effective Hamilton ians for conjugated pi-electron systems. This method is based on the m inimization of the difference between the ground state reduced single electron density matrix calculated from the effective Hamiltonian and its ab initio counterpart under a set of well-defined constraints. App lications are made to various oligomers of polymethineimine (PMI), pol yazine (PAZ) and polyazoethene (PAE) at the Hartree-Fock level. Calcul ated are also the optical gaps of these oligomers. The effective Hamil tonians contain electron-electron Coulomb interactions and are suitabl e for the study of excited state dynamic processes such as nonlinear o ptical properties in pi-conjugated systems. (C) 1998 American Institut e of Physics.