Geometric, Electronic, and Optical Properties of Monomer and Assembly of Endohedral Aluminum Superatomic Clusters

Density functional computations are used to evaluate the geometric, electronic, and optical properties of endohedral aluminum clusters X@Al-12 (X = B, Al, Si, P) and their assemblies. All X@Al-12(+/0/-) clusters are perfect or slightly distorted icosahedral structures, with the exception of Al-13(+), which is highly distorted. The projected density of states (PDOS) onto the spherical harmonics of monomers clearly reveals superatom behavior and electron shell closings of F orbitals in a 40-electron species. The electronic absorption spectrum of SiAl12 is analyzed in terms of the superatom orbitals. The optimized structures of X@Al-12-Y@Al-12 (X-Y = Si-Si, B-P, Al-P) dimers are constructed by facing the sides of the monomers in a staggered fashion. The PDOS of the dimers mostly exhibit five hybridizations: S, P, SD, PF, and SDG. The exceptions are HOMO, which possesses a DFG hybridized character and lies between the PF and SDG regions, and LUMO, which possesses a DG hybridized character. By analyzing the simulated absorption spectra of the B@Al-12-P@Al-12 and Al-13-P@Al-12 heterodimers, charge transfers from B/Al@Al-12 to P@Al-12 are found in the visible region, weakly accompanying the opposite charge transfer. The heterodimers have substantial charge carriers, estimated as the difference in electron counts from the closed-shell Si@Al-12, with slight charge depletions (similar to 0.2). The charge distributions in B@Al-12 and P@Al-12 are essentially unaltered by the insertion of Si@Al-12 into the heterodimer, resulting in that the heterotrimer possesses a larger dipole moment than the heterodimer.