On metal clusters below 2 nm, the electronic states are discrete, and the catalytic properties depend on the spacing around the Fermi level, resulting in a quantum size effect. In addition, for metal clusters with filled d-electrons, the s-shell effects also have an impact on the size of the gap around the Fermi level, especially near a shell closing. We are interested in finding a way to separate these electronic effects from other phenomena that exist at this length scale. We have used density functional theory to study the finite-size effects on relaxed gold and platinum clusters, ranging from 13 to 923 atoms, as well as, on their island analogs that have no shell structures or gaps around the Fermi level. Calculations of this size have been made possible by leadership computing resources, containing up to 40,960 nodes, at Argonne National Laboratory. Looking at the density of states, a metal-like band structure starts to form at around 147 atoms. Oscillation in oxygen binding was observed on gold particles, consistent with oscillations in the Fermi-level due to s-shell effects. We find that gold particles experience significant quantum size effects below the critical size of 561 atoms. In contrast, quantum size effect ends more quickly on platinum, at only 147 atoms.

Finite-size effects on gold and platinum clusters

247th National Meeting (2014)

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