Electronic Properties of Small Neutral and Charged Beryllium Clusters

We determine the atomic and electronic structures for neutral and singly positively chargedberyllium clusters containing from two to six atoms using density functional theory in the local spin density approximation. Ions are moved with a steepest descent method and the electronic wave functions optimized using a fictitious dynamics with simulated annealing, as conceived by Car and Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]. Shell-like orbitals, filling angular momentum states in the order: 1s 1p 2s 1d are obtained. We employ a Mulliken population analysis using an atomic basis to examine how the shell orbitals arise from atomic orbitals. This analysis also allows us to associate the electron density distribution and, in the case of a charged cluster, the distribution of the hole with atomic sites and with regions of overlap between atom pairs. We show quantitatively that the contribution to the bonding density from delocalization of the 1s state is hampered by the appearance of the antibonding 2s state. In the case of charged clusters we observe the tendency of the hole to distribute itself near the most exterior atomic sites in geometries of high symmetry. Keywords