Linear and nonlinear optical response of dimethyl-amino-nitro-stilbene (DANS): Coupled oscillator representation versus sum-over-states picture

The first-, second-, and third-order optical polarizabilities of dimethyl-amino-nitro-stilbene (DANS) have been calculated on the basis of a coupled oscillator picture and compared to the results obtained within the sum-over-states formalism. The two approaches lead to a very similar description for both static and dynamic responses. The correspondence between the nature of the dominant oscillators and the essential excited states contributing primarily to the linear and nonlinear optical response is emphasized.