Evolution of the structural and bonding properties of aluminum-lithium clusters

Abstract

We report a detailed study of the electronic structure, energies, and the nature of bonding in various Al-Li clusters: Al_nLi_n(n=1-11), Al₂^-, Al₂^2-, Al₂Li, Al₂Li^-, and Al₆Li₈. We use the standard Born-Oppenheimer molecular dynamics within the framework of density-functional theory. The growth structure in these clusters is found to occur in two broad categories: the first (for n=2-4) has the structure of a bent rhombus, and the second (n=7-9,11) has the structure of a pentagonal ring. A substantial charge transfer between the atoms is observed in nearly all the clusters with the exception of Al₂Li₂. In this cluster, a hybridization of the 2s orbital of Li with the 3p orbital of Al is observed. In clusters with more than six Al atoms, the eigenvalue spectrum is divided into two main groups: at the lower end of the energy spectrum, jelliumlike orbitals are observed, while at the higher end, localized bonds are seen. The localized bond formation appears to result from the interaction between p electrons on each of the Al atoms. We also have found a tetravalent structure for Al atoms within the Al-Li cluster arising due to a charge transfer from the Li atoms to the Al atoms.