Affiliations: [a] Departamento de Matemáticas y Computación, Escuela Politécnica Superior, Universidad de Burgos, Burgos, Spain | [b] Center for Atomic-Scale Materials Design, Department of Physics, Building 307, Technical University of Denmark, DK-2800 Lyngby, Denmark | [c] Departamento de Física Teórica, Atómica y Óptica, Universidad de Valladolid, Valladolid, Spain | [x] Department of Chemistry, University of Patras, Greece | [y] Department of Physics, University of Patras, Greece
Abstract: We report on first-principles quantum mechanical optimizations of the minimum energy equilibrium structure of neutral, Sin, and anionic, Sin−, pure silicon clusters, as well as the isoelectronic SinM doped clusters (M=Sc−,Ti,V+) for n=14–18. We have published previously some of these results, but additional analysis is contributed here for the first time, particularly for the pure anionic silicon clusters and doped SinTi compounds. The lowest energy isomer of the anionic Sin− cluster shows different geometry than the neutral cluster, except for n=15,17. The geometries of a few low-lying energy isomers of doped SinM does not relate to those of pure silicon clusters in the range of sizes considered in this work. For both pure and doped Si clusters, we analyze the trend of several electronic properties with the cluster size, like the binding energy, the addition energy of the impurity M to pure Si clusters, the second difference of total energy, the Homo-Lumo gap, the average Si-Si and Si-M distance, and the electron affinity. For Si16M doped clusters we found the largest binding energy, the highest second difference of energy, and the highest Homo-Lumo gap. These facts are manifestations of the special stability of Si16M clusters found in recent experimental mass spectra, which was rationalized in previous works as a combination of geometrical (near spherical cage-like structure) and electronic effects (l-selection rule of the spherical potential model). Here we present additional arguments, by comparing the partial orbital density of states of the near-spherical Frank-Kasper isomer of Si16Ti, with that of a non-spherical isomer of Si16Sc− anion. We have also computed the adiabatic electron affinity of pure and doped Si clusters. For doped clusters, the computed electron affinities are in very good agreement with available estimations from experimental photoelectrons spectra, but for pure neutral clusters the calculations underestimate by more than 18% the experimental values.
Keywords: Electronic and geometrical properties, stability, silicon-doped clusters
