Localized-density-matrix, segment-molecular-orbitals and poly(p-phenylenevinylene) aggregates

The segment-molecular-orbital representation is developed and incorporated into the recently developed linear-scaling localized-density-matrix method. The entire system is divided into many segments, and the molecular orbital s of all segments form the basis functions of the segment-molecular-orbital representation. Introduction of different cutoff lengths for different seg ment-molecular-orbitals leads to a drastic reduction of the computational c ost. As a result, the modified localized-density-matrix method is employed to investigate the optical responses of large Poly(p-phenylenevinylene) agg regates. In particular, the interchain excitations are studied. The complet e neglect of differential overlap in spectroscopy hamiltonian is employed i n the calculation. (C) 1999 American Institute of Physics. [S0021-9606(99)3 0446-3].