DFT/TDDFT study of electronic and optical properties of Surfacepassivated Silicon nanocrystals, Sin (n 5 20, 24, 26 and 28)

Density functional theory and Time-dependent density functional theory (TDDFT)-based calculations were performed on surface-passivated Silicon nanocrystals (SPSNs) of different sizes. The surface passivation was achieved using H, F and Cl atoms. Various properties of the resulting optimized structures SinHn, Sin Hn-1F and SinHn-1Cl (n = 20, 24, 26 and 28) like binding Energy, dipole moment, HOMO–LUMO gap, vibrational IR spectra and absorption wavelengths were determined. Surface passivation studies reveal that all the SPSNs are insulators and TDDFT study performed using two basis sets 6-31G and 6-31?G (d,p) shows that the maximum optical absorption of all the samples lie in the UV region, except for Si28H27F SPSN which shows maximum absorption at *588 nm. The absorption transitions in the SinHn, Sin- Hn-1F and SinHn-1Cl were characterized to be from pi?pi* transitions.