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

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Abstract
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.