Structure and Properties of (GaAs)n Clusters

Electronic and geometrical structures of neutral (GaAs)(n) clusters are computed using density functional theory with generalized gradient approximation and relativistic effective core potentials for n = 17-40, 48, and 54. To assess the accuracy of this approach, all-electron calculations are performed for smaller (GaAs)(n) clusters with n = 2-12 as well as for several isomers of (GaAs)(20). We examined the energetic preference of tubular vs non-tubular cages with increasing n and found that tubular cages are generally lower in total energy than the other cage isomers. Along with the cage structures, we probed structures cut off from a zinc-blend lattice, tailoring the surface atoms in such a way as to have no dangling bonds. The lowest energy state of (GaAs)(36) is found to have a bulk-like structure with 12 tetrahedrally coordinated inner atoms. We found that the HOMO-LUMO gap converges to the bulk GaAs value as n increases. Static electric dipole polarizability per atom of the cage structures does increase as n increases and exceeds substantially the GaAs bulk value