Si78 double cage structure and special optical properties†
We performed first-principles calculations to study the structural stability of Si78 clusters with or without hydrogen passivation. The calculations reveal that an endohedral double cage isomer is more stable than the diamond-like structure, whereas the opposite is found for the hydrogen passivated isomers. In particular, the hydrogenated double cage and diamond-like structure may display blue shifts to the visible and UV regions, respectively. The IR vibration spectra, ionization potential (IP) and electronic density-of-states of the clusters were calculated and discussed.