Real time approach for non-linear optical response of nano-scale systems

We present a real-time, time-dependent density-functional approach for the calculation of the frequency-dependent linear and non-linear optical response, which is based on the approach of Tsolakidis et al.\footnote{A. Tsolakidis, D. Sanchez-Portal and R.M. Martin, Phys. Rev. B {\bf66}, 235416 (2002).} Tensor components of linear polarizabilities and first order hyper-polarizabilities are extracted by fitting net time dependent polarizations with different electric field strengths. The method is computationally efficient and can be applied to large, molecular and nano-scale systems. Results are presented for C$_{60}$ and for a number of ``push-pull" molecules. Our results for the static limit are in good agreement with other density-functional calculations.