DENSITY-MATRIX-ELECTRONIC-OSCILLATOR REPRESENTATION OF OPTICAL SPECTROSCOPY OF SEMICONDUCTOR NANOCRYSTALS

The optical response of CdSe semiconductor nanocrystals is investigate d using the reduced single-electron density matrix in real space, calc ulated by means of the time-dependent Hartree-Fock technique. The spec troscopic signatures of exciton confinement are analyzed using the fre quency-dependent electronic coherence matrix (off-diagonal density-mat rix elements). The effects of Hartree and the Fock (exchange) type Cou lomb interactions on the exciton binding energy are discussed. The lat ter result in almost dark excitons situated energetically below the ma in transition. Off-diagonal Coulomb matrix elements lead to larger exc iton binding energies compared with previous calculations, and result in a better agreement of the size dependence of the lowest optical tra nsition with experiment. (C) 1997 American Institute of Physics.