Structural and Electronic Properties of Medium-Sized Aluminum-Doped Boron Clusters AlBn and Their Anions

Binary boron-based compounds are expected to possess unique molecular architecture and chemical bonding. Here, we explore how incorporation of a valence isoelectronic Al atom into boron clusters containing from 10 to 20 atoms modifies the structures and properties of the initial clusters. The global minima structures of neutral and anionic Al-doped boron cluster in the size range from 10 to 20 have been identified using the Crystal structure AnaLYsis by Particle Swarm Optimization method. The states with the promising geometrical structures are reoptimized using density functional theory and triple-zeta basis sets. It is found that the geometries of the ground states of the AlBn and AlBn- clusters possess planar, quasi-planar, and exohedral topologies. A nearly circular planar AlB18- cluster with C-2v symmetry and a large energy gap 2.98 eV has been discovered. The calculated photoelectron spectra of the anions are well in accord with the experimental spectra. The chemical-bonding analysis suggests that both large HLG and double pi-aromaticity have much contribution to the electronic stability of AlB18- cluster. Our results elucidate the structural growth behavior of Al-doped boron clusters and enrich the growth pattern and chemical bonding nature of boron-based clusters.