The effect of palladium and platinum doping on the structure, stability and optical properties of germanium clusters: DFT study of PdGen and PtGen (n=1-20) clusters

Structural, electronic and optical properties of germanium clusters doped with palladium and platinum atoms MGen (M = Pd,Pt and n = 1-20) are investigated in the framework of the density-functional theory. From n >= 10 or 11, the cage-like structures where the doping atom is totally encapsulated inside a Ge-n cage are favored. Relative stabilities of different MGen clusters have been analyzed from the average binding energies, second energy differences, HOMO-LUMO gap, and the vertical ionization potential and electronic affinity. Our results show that the clusters of MGen (M = Pd,Pt) with n = 10, 12, 16 and 18 exhibit relative high stability. Optical absorption spectra are predicted to be unable to discriminate the endohedral and exohedral structures.