Electronic structure and bonding in clusters: Theoretical studies

Abstract

The electronic structures of small Aln, n=5, 9, 13, clusters with bulk geometry are studied using the ab initio Hartree-Fock-LCAO method. The cluster ground states have always multiplicity higher than the lowest possible value. However, the energy difference between ground and lowest low spin state decreases with increasing cluster size. The energy range of the Aln cluster valence levels is comparable with the width of the occupied part of the 3 sp band in bulk Al. The different binding mechanisms that arise when a CO molecule interacts with Aln clusters in different coordination sites are analyzed in detail with the constrained space orbital variation (CSOV) method. Electrostatic and polarization contributions to the interaction are found to be important. Among charge transfer (donation) contributions π electron transfer from Aln to CO corresponding to π backbonding is energetically more important than σ electron transfer from CO to Aln characterizing the σ bond. © 1986 Springer-Verlag.