The structures, densities of electronic states, and HOMO-LUMO gaps of surface-passivated ZnSe and CdTe
nanocrystals are calculated using a first principles density functional pseudopotential method. The calculations
are performed in real space without an explicit basis. The surfaces of the nanocrystals are passivated using
fictitious partially charged hydrogen atoms. The value of the fractional charge is selected according to the type
of covalent bond. The results of these calculations show that the fractional charge approach effectively removes
the electronic states associated with the surface hydrogen atoms from the gap of group II-VI semiconductor
nanocrystals. At the same time, the energies of the other electronic states are not significantly affected by the
presence of partially charged hydrogen atoms on the nanocrystalline surface.
We apply first-principles computational methods to study the surface energy and surface stress of silver and
aluminum nanoparticles. The structures, cohesive energies, and lattice contractions of Ag and Al nanoclusters
are analyzed using an ab initio density functional pseudopotential technique combined with the generalized
gradient approximation for the exchange-correlation functional. Our calculations predict the surface energy of
Ag and Al nanoclusters to be in the range of 1.1-2.2 J/m2 and 0.9-2.0 J/m2, respectively. These values are
consistent with the surface energies of bulk silver and aluminum. The surface stress is estimated from the average
lattice contraction by considering the hydrostatic pressure on the surface of a spherical particle. A comparison
of the calculated surface energies and stresses indicates a significantly greater degree of surface reconstruction in
Al clusters than in Ag clusters.
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