Theoretical study of aluminum arsenide clusters:: Equilibrium geometries and electronic structures of AlnAsn (n=1-4)

The geometry, electronic configurations, harmonic vibrational frequencies and stability of the structural isomers of AlnAsn clusters (n=1-4) have been investigated using density functional theory. For dimers and trimers, the lowest energy structures are planar cumulenic rings (IIs, VIs) with D-nh symmetry. The caged structure with T-d symmetry (IXs) lie lowest in energy among the tetramers. The Al-As bond dominates the structures for many isomers so that one preferred dissociation channel is loss of the AlAs monomer. The atomic charges, hybridization and chemical bonding in the different structures are also discussed. Comparisons with valence-isoelectronic Si-2n, AlnPn and GanAsn clusters of same size, the properties of the aluminum arsenide clusters are analogous to those of their corresponding AlnPn,Si-2n counterparts. The results can explain the modification and refinement of Si phase in Al-Si alloy in the molecular level. (C) 2005 Elsevier Inc. All rights reserved.