Density Functional Theory Study on the Structures and Electron Affinities of Neutral Asn and Anionic Asn-(n=2～5) Clusters

Three density functional theory approaches: the local-spin-density approximation Slater-VWN functional, the gradient-correction Becke88-LYP functional and the hybride Becke3-LYP functional are used in the geometry optimizations and frequency calculations on Asn(n=2~5) clusters and their anionic clusters, with 6-311+G(3df) basis sets. Several possible structures for each cluster sizenof neutral and anionic clusters have been investigated. Their equilibrium structures have been found. The equilibrium structures of neutral Asnclusters obtained in the present DFT calculations are compared with other theoretical results in literature and experimental data. The agreement between them is very good. The equilibrium structures of anionic Asn-clucters are predicted. The most stable structures of anionic Asn-(n=3~5) clucters determined by DFT calculations are as follows: a isosceles triangle (C2v) forAs3-, a roof-type(C2v) forAs4-, a pentagon(D5h) for As5-. These most stable structures of anionic Arsenic clusters are similar to those of anionic clusters formed by other group V elements including P, Sb, Bi. The adiabatic electron affinities (EAa) of these arsenic clusters are also calculated,which is in good agreement with the experimentalEAavalues of Asnclucters from the work by Lippaet al.The present theoretical study shows that Jahn-Teller effect is very obvious in determining the stable structure of Arenic clusters. In the D3hstructure of As3, the Td structure of As4-, and the D5hstructure of As5, the highest occupied molecular orbital(HOMO) for one structure in the ground state is all degenerate. These degeneracies result in Jahn-Teller distortions and make these structures with high symmetries unstable.