Finite-field approximation, optical properties

One of the main properties of interest in the field of conjugated polymers is the study of their dynamic nonlinear optical (NLO) response [112, 113]. It is a major challenge to obtain reliable dynamics of interacting electron systems. While for short oligomers there exist reasonable approximations for computing these properties [114], for longer chains even within model Hamiltonian approximations, the dynamic NLO coefficients had proved elusive. Yet most interest lies in the longer chains since the dynamic NLO properties exhibit dominant finite-size effects. 

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