OICC Press Journal of Nanostructure in Chemistry 2193-8865 5 2 (June 2015) 2015 02 24 DFT/TDDFT study of electronic and optical properties of Surface-passivated Silicon nanocrystals, Sin (n = 20, 24, 26 and 28) 10.1007/s40097-015-0150-5 EN S. Chopra Department of Physics, AIAS, Amity University, Noida, IN B. Rai Department of Physics, AIAS, Amity University, Noida, IN Journal Article 2015 02 24 Abstract 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 Si n H n , Si n H n−1 F and Si n H n−1 Cl ( 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 Si 28 H 27 F SPSN which shows maximum absorption at ~588 nm. The absorption transitions in the Si n H n , Si n H n−1 F and Si n H n−1 Cl were characterized to be from pi→pi* transitions. Graphical Abstract