DENSITY-FUNCTIONAL STUDY OF PHOSPHORUS AND ARSENIC CLUSTERS USING LOCAL AND NONLOCAL ENERGY FUNCTIONALS

Previous calculations of the structures of isomers of phosphorus clusters up to P11 (density functional calculations with simulated annealing, local spin density approximation to the exchange-correlation energy) have been extended to arsenic clusters. The structures of As(n) clusters are characterized by an almost uniform expansion (approximately 9%) of the corresponding P(n) isomers. All cluster isomers have also been studied using a nonlocal, gradient corrected (Becke-Perdew) energy functional. While the structures are almost unchanged, there are significant improvements in the cohesive energies of all clusters. We present a simple picture to show that the improvements arise from contributions both in the atoms and near the ''surface'' of the clusters.