Linear scaling calculation for optical-absorption spectra of large hydrogenated silicon nanocrystallites

A linear scaling calculation of the optical-absorption spectra is performed for hydrogenated silicon nanocrystallites up to 13 464 Si atoms. The calculation is performed in real space and is based on a time-dependent representation of the linear-response function. The empirical pseudopotential method is used for potentials of silicon and hydrogen atoms. The peaks in higher excited states in the ultraviolet region of the calculated absorption spectra are shown to shift to higher energy with a decrease in size.