Geometrical and electronic structures of small Wn (n=2-16) clusters

The geometrical and electronic structures of W-n (n=2-16) clusters are investigated within the framework of a gradient-corrected density functional theory. The close-packed configurations are preferred for small tungsten clusters up to n=16. The most energetic favorable structures of W-14, W-15, and W-16 clusters, exhibiting similar electronic band structures, are all formed based on body centered cubic (bcc) unit. The clusters with size of n=8, 12, and 15 are found to be more stable with respect to their respective neighbors. The analyses of atomic orbit projected density of states and highest occupied molecular orbital, lowest unoccupied molecular orbital isosurfaces indicate that 5d electrons play a dominant role in the chemical activities of tungsten clusters. The clearly s-d hybridizations are primary presented in bonding W atoms of smaller clusters, as the cluster sizes increase, the 6p orbitals are gradually involved in chemical bonding. Our calculated vertical ionization potentials (VIPs) indicate that the W-8 and W-12 clusters correspond to the high VIPs. The vertical electron affinities are slightly underestimated in our investigation, but follow the trends of experimental data in principle.