The localized-density-matrix method Chen, G. H. Chem. Phys. Lett. 1998, 292, 379) is employed to simulate the optical responses of very large carbon nanotubes and polyacetylene oligomers containing 10 000 carbon atoms. The Pariser-Parr-Pople Hamiltonian is used to describe the π electrons in these systems, and the time-dependent Hartree-Fock approximation is employed to calculate the linear optical responses. In the calculation, the fast multipole method or the cell multipole method is employed to evaluate the effects of Coulomb interaction. It is illustrated that the computational time scales linearly with the system size for carbon nanotubes while high accuracy is achieved.

No abstract

Photo-induced electronic excitations of poly(p-phenylenevinylene) (PPV) aggregates are simulated and characterized using a recently developed linear-scaling localized-density-matrix (LDM) method. The intra-and inter-chain components of excitations are analyzed and quanti®ed for dierent inter-chain distances. The excitations for the absorption and luminescence in PPV ®lm and its derivatives are identi®ed and are found analogous to those of H-aggregates. Their energy shifts upon aggregation are determined mainly by the inter-chain kinetic energy reduction and the Coulomb interaction of the electron±hole pair. It is concluded that the luminescence is caused by the intra-chain electron±hole pairs. Ó

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 orbitals of all segments form the basis functions of the segment-molecular-orbital representation. Introduction of different cutoff lengths for different segment-molecular-orbitals leads to a drastic reduction of the computational cost. As a result, the modified localized-density-matrix method is employed to investigate the optical responses of large Poly(p-phenylenevinylene͒ aggregates. In particular, the interchain excitations are studied. The complete neglect of differential overlap in spectroscopy hamiltonian is employed in the calculation.

No abstract