AB-INITIO STUDIES OF THE ELECTRONIC-STRUCTURE OF BE-93, BE-105, BE-111, AND BE-123 CLUSTERS

Ab initio self-consistent-field calculations are reported for electron ic states of beryllium clusters comprised of 93, 105, 111, and 123 ato ms. The respective clusters correspond to coordination shells 12-15 of a central Be atom with internuclear separations derived from the latt ice constants of the bulk metal. Ab initio effective core potentials h ave been employed to replace the Is electrons, thereby reducing the co mplexity of the calculations. In addition, use of the full D-3h point group symmetry of the clusters results in a substantial reduction of t he numbers of two-electron integrals that must be computed and process ed. Binding energies, orbital energies, electric field gradient, nucle ar-electrostatic potential, diamagnetic shielding constant, second mom ents, and Mulliken populations are calculated for selected electronic states. Calculated binding energies when compared among the different clusters as well as to smaller and larger fragments from earlier studi es provide evidence for the onset of convergence to the Hartree-Fock l imit of the bulk. Lowest-state ionization potentials are consistently above and agree to within 14% of the experimental workfunction. The ne t charge on the central beryllium atom decreases toward zero. The vari ability of observed bulklike behavior for the different properties ind icates that the transition between cluster and bulklike behavior is no t sharp and depends on the quantity of interest. (C) 1995 John Wiley a nd Sons, Inc.