Size-consistent quasiparticle representation of nonlinear optical susceptibilities in many-electron systems

The optical response of a many-electron system is calculated by mapping it onto a coupled set of classical oscillators representing the electron-hole pair components of the reduced single-electron-density matrix. This classical representation is rigorously established using a Poisson bracket relation. Expressions for the nonlinear optical susceptibilities obtained using a Green's-function solution of the oscillator equations of motion are used to analyze the size scaling of the off-resonant response and the resonant structure of the response. (C) 1996 American Institute of Physics.