Palestrante:Seminário do DFMC - Dr. Anderson Silva Chaves (UNICAMP- IFGW - DFMC)

Resumo:

The knowledge of the atomic structure of metal nanoclusters stabilized by ligands is a necessary prerequisite to understand their physical and chemical properties. However, our atom-level understanding is far from satisfactory, for instance, as for 55-atom Pt and Au nanoclusters. Here, we report a density functional investigation of the role of ligand effects using the PH3 (one lone-pair) and SH2 (two lone-pairs) molecules on the relative stability of the Pt55 and Au55 nanoclusters. In gas-phase, distorted reduced core (DRC) structures with 7 to 9 atoms in the core region are about 5.34 eV (Pt55) and 2.20 eV (Au55) lower in energy than the icosahedron (ICO) model with Ih symmetry and 13-atoms in the core. However, the stability of the ICO structure increases by increasing the number of ligands from 1 to 18, in which both DRC and ICO structures are nearly degenerated in energy at the limit of 18 ligands, which can be explained as follows. In gas-phase, there is a strong compr ession of the cationic core-region by the anionic surface atoms (Coulomb interactions), and hence, the strain release in gas-phase is obtained by reducing the core size (number of atoms), which leads to the distorted reduced core structures. However, the addition of ligands on the anionic surface reduces the charge transfer between core and surface regions, which contributes to decrease the Coulomb interactions and the strain on the core region of the ICO structure, and hence, it stabilizes a compact ICO structure. Our insights are supported by several structural, electronic, and energetic analysis.