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

We present a systematic study of the photo-absorption spectra of various SinHm 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 SiH4 and Si2H6 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.

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► The PA spectra of Si and hydrogenated Si clusters is calculated using TDDFT.
► For singly hydrogenated clusters we find that the PA spectra is red-shifted.
► The above effect diminishes with increase in Si atoms.
► For fully hydrogenated clusters the PA spectra is blue shifted.
► Hydrogenation can be used to manipulate the optical gaps for silicon nano-clusters.