Structural Evolution and Electronic Properties of TaSin-/0 (n = 2-15) Clusters: Size-Selected Anion Photoelectron Spectroscopy and Theoretical Calculations

The structural evolution and electronic properties of TaSi_n^-/0 (n = 2-15) clusters are explored using anion photoelectron spectroscopy accompanied by quantum chemical calculations. The Ta atom in TaSi_n^-/0 is inclined to interact with more Si atoms and has high coordination numbers. The theoretical calculations show that TaSi₂^-/0 have trianglur structures and TaSi₃^-/0 adopt pyramid structures, while the geometries of TaSi_n^-/0 (n = 4-7) are all exohedral structures dominated by bipyramid-based configurations with the Ta atom face-capping the Si_n motifs. TaSi₈^-/0 and TaSi_9-10^- have boat-shaped geometries, whereas TaSi_9-10 neutrals adopt bipyramid-based geometries instead of boat-shaped ones. TaSi₁₁^- and TaSi₁₂ are confirmed as the critical size of transiting from exohedral to endohedral structures for anionic and neutral clusters, respectively. TaSi_12-15^-/0 have pentagonal or hexagonal prism-based geometries. Natural population analysis shows that the electron transfers from Si_n skeletons to Ta atom. The second-order energy differences (Δ₂E) and incremental binding energy (ΔE^I) values exhibit strong odd-even alternations, suggesting that the TaSi_n-odd^-/0 clusters are more stable than the adjacent TaSi_n-even^-/0 ones, except that TaSi_12^-/0 are more stable than TaSi_11^-/0 and TaSi_13^-/0.

Appearance of V-encapsulated tetragonal prism motifs in VSi10- and VSi11- clusters

The structural and electronic properties of V-doped silicon clusters, VSi10-/0 and VSi11-/0, were investigated by using mass-selected anion photoelectron spectroscopy in combination with theoretical calculations. Photoelectron spectroscopy of VSi10- and VSi11- clusters with spectral similarity reveals that the two cluster structures resemble each other. Interestingly, theoretical calculation studies provide definitive evidence of the global minima for the two clusters to be V-encapsulated tetragonal prism motifs with extra Si atoms bicapped and tricapped, respectively. The enhanced stability of the tetragonal prism unit in VSi10- and VSi11- is due to the strong interactions between 3d (V) and 3p (Si) orbitals, and more charge transfers from the Sin framework to the encapsulated V atom. The tetragonal prism unit possessed by both the VSi10- and VSi11- clusters is observed for the first time in the current work, and may offer new ideas in developing components for Si-based nanodevices.

Structural and electronic properties of exohedrally doped neutral silicon clusters LnSin (n = 5, 10; Ln = Sm, Eu, Yb)

Lanthanide-doped silicon clusters have been extensively studied in the fields of optoelectronics, magnetism and nanomaterials during the last decade. Herein, systematic structure searches for typical neutral clusters of lanthanide-doped silicon clusters LnSin (n = 5, 10; Ln = Sm, Eu, Yb) have been performed by means of density functional theory coupled with the "stochastic kicking" global search technique. It is found that the Ln atom in LnSin prefers to locate on the surface of Sin to form an exohedral structure, and this exohedral configuration may dominate the nascent structure of LnSin. The spin density and Mulliken population analyses indicate that LnSin clusters possess remarkable magnetic moments (except for YbSin), which are mainly supplied by the Ln 4f electrons (except for Yb). Density of states visually shows the significant spin polarization for open-shell structures of SmSin and EuSin. As for the YbSin (n = 5, 10) system, it has a closed-shell electronic structure with a large HOMO-LUMO gap of 2.72 eV. Bonding analysis, including localized orbital locator and electron density difference, shows that the Si-Si covalent interaction and Sm-Si electrostatic interaction are important for the structural stability of LnSin.

B12-containing volleyball-like molecule for hydrogen storage

A stable core-shell volleyball-like structure of B12@Li20Al12 has been proposed using first-principles calculations. This structure with T h symmetry is constructed with a core structure of I h-B12 and a volleyball-like shell of Li20Al12. Frequency analysis and molecular dynamics simulations demonstrate the exceptional stability of B12@Li20Al12. The chemical bonding analysis for B12@Li20Al12 is also conducted to confirm its stability and 46 multi-center two-electron σ bonds are observed, which are widely distributed throughout the core-shell structure. For the hydrogen storage capacity of the B12@Li20Al12, our calculated results indicate that about 58 H2 molecules can be absorbed at most, leading to a gravimetric density of 16.4 wt%. The exceptionally stable core-shell volleyball-like B12@Li20Al12 combined with its high hydrogen storage capacity indicates that it can be one of the outstanding hydrogen storage materials of the future.

Au20Si12: A hollow Catalan pentakis dodecahedron

A stable hollow Au₂₀Si₁₂ cage with I_h symmetry has been predicted using first-principles density functional theory. The stability of the cage-like Au₂₀Si₁₂ structure is verified by vibrational frequency analysis and molecular dynamics simulations. A relatively large highest occupied molecular orbital-lowest unoccupied molecular orbital gap of 1.057 eV is found. Electronic structure analysis shows that clearly p-d hybridizations between Si atoms and Au atoms are of great importance for the stability of Au₂₀Si₁₂ cage. The cage-like Au₂₀Si₁₂ structure may have potential applications in semiconductor industry and microelectronics.

Cu20Si12: A Hollow Cage Constituted of a Copper Dodecahedron and a Silicon Icosahedron

A stable hollow copper silicide cage with Ih symmetry, Cu20Si12, constituted of a copper dodecahedron and a silicon icosahedron, was investigated using density functional theory. Molecular dynamics simulations show that Cu20Si12 retains its geometric topology up to an effective temperature of about 962 K. The molecule has a HOMO-LUMO gap of 1.099 eV, indicating its relatively high chemical stability. These frontier molecular orbitals show clear characteristics of hybridization between Si 3p and Cu 3d electrons. This proposed structure helps to extend the range of high-symmetry molecular polyhedral species. The hollow space within Cu20Si12 can be used to accommodate other atoms or molecules and emphasizes the benefit of studying endohedral fullerenes.

Sc20C60: a volleyballene

An exceptionally stable hollow cage containing 20 scandium atoms and 60 carbon atoms has been identified. This Sc20C60 molecular cluster has a Th point group symmetry and a volleyball-like shape that we refer to below as "Volleyballene". Electronic structure analysis shows that the formation of delocalized π bonds between Sc atoms and the neighboring pentagonal rings made of carbon atoms is crucial for stabilizing the cage structure. A relatively large HOMO-LUMO gap (∼1.4 eV) was found. The results of vibrational frequency analysis and molecular dynamics simulations both demonstrate that this Volleyballene molecule is exceptionally stable.

Structures and electronic properties of silicene clusters: a promising material for FET and hydrogen storage

Structures and electronic properties of clusters of an all-Si analogue of graphene, silicene, have been studied through quantum chemical calculations. The structures of the six-membered rings show interesting chair like puckering, which for large sheet-like clusters form ordered ripples. Binding energies, HOMO-LUMO gaps and polarizabilities for the silicene clusters show interesting monotonic trends analogous to polyacenes. Stacking of two silicene layers leads to the formation of closed 3D clusters with high symmetry and strong Si-Si bonds. The heat of hydrogenation of silicene to form silicanes is overwhelmingly exothermic and leads to the opening up of the HOMO-LUMO gaps. Thus, analogous to graphanes, silicanes are predicted to be interesting materials for hydrogen storage and for their band engineering properties.