The difference between oxide and hydrogen passivation of small Si nanocrystals is explored by all-electron, hybrid functional DFT calculations with unrestricted geometry optimization. Oxide passivation lowers the band gap by about 2.4 eV for Si35 cores and by about 1.5 eV for Si66 cores. The oxide-passivated nanocrystals have optically forbidden, indirect-gap-type transitions whereas the hydrog...
