Ab initio calculation of second-harmonic-generation at the Si(100) surface- art. no. 205406

We present a microscopic, first-principles calculation of the second-harmon ic spectra of clean and Hydrogenated Si(100) surfaces. The differences betw een theoretical spectra obtained for different reconstructions, namely the 2 X 1 and the c(4 X 2) ones, are dramatically enhanced with respect to thos e obtained in linear optical response. The calculated spectral features are analyzed in detail, studying their relations with those of bulk and surfac e linear optical spectra. The inclusion of quasiparticle effects within the scissors operator approximation yields theoretical spectra in good agreeme nt with the experiments.