Photo-absorption spectra of small hydrogenated silicon clusters using the time-dependent density functional theory

Abstract

We present a systematic study of the photo-absorption spectra of various Si n H m clusters ( n = 1 – 10 , m = 1 – 14 ) using the time-dependent density functional theory (TDDFT). The method uses a real-time, real-space implementation of TDDFT involving full propagation of the time dependent Kohn–Sham equations. Our results for SiH 4 and Si 2H 6 show good agreement with the earlier calculations and experimental data. We study the photo-absorption spectra of silicon clusters as a function of hydrogenation. For single hydrogenation, we find that in general, the absorption optical gap decreases showing a significant red shift for small sized clusters and as the number of silicon atoms increases the effect of a single hydrogen atom on the optical gap diminishes. For further hydrogenation the optical gap increases and for the fully hydrogenated clusters the optical gap is larger compared to corresponding pure silicon clusters corresponding to a blue shifted spectra.