Endohedrally doping the gold cage Au16- with an trivalent atom B, Al, Ga, and In: Density functional studies

It can be observed from the figure that the HOMOs of M@Au16--center are almost isoenergetic, however, the LUMOs of them shift upward much compared to that of Au16-. Therefore, the central M obvious enlarge the Eg by occupying the HOMO of Au16-, producing the larger Egs of 1.60, 1.30, 1.73, and 1.37 eV for M@Au16--center (M = B, Al, Ga, and In) respectively. Then, the LUMO + 1 of Au16- become the LUMOs of M@Au16--center. Therefore, the HOMOs ofM@Au16--center should be partly occupied by the M atom, while the LUMO of them should be mostly from the Au16- bodies. This scenario can be clearly seen from the wave functions of their HOMOs and LUMOs in figure, where the blue and yellow represent the negative and positive parts of the wave functions respectively.