Dirac scattered-wave study of trigonal bipyramidal silver clusters Ag ₅^q+ (q=0,2-4)

The electronic structure of the neutral and cationic pentaatomic silver bare clusters is investigated by the Dirac scattered-wave (DSW) method. The results indicate that there is significant 5s_1/2-4d_5/2 hybridization in the bonding molecular orbitals, due to relativistic effects. Molecular hyperfine interactions (hfi) are calculated for the paramagnetic species Ag₅^q+ (q = 0, 2, and 4) through a first-order perturbation to the Dirac Hamiltonian. The ground state (²E′) orbital degeneracy of Ag₅ in D_3h geometry is removed by spin-orbit interaction leading to Kramers degeneracy, and consequently the D_3h geometry of Ag₅ will not distort due to Jahn-Teller effect. It is found that the hyperfine coupling constants calculated by using a four-component wave function for the Ag₅²⁺ and Ag ₅⁴⁺ clusters differ significantly from previously computed hfi using a second-order perturbation to the Schrödinger Hamiltonian. First ionization potentials and excitation energies are predicted for all the species as calculated by the spin-restricted transition state method.