ABINITIO CALCULATIONS OF AN M-CENTER ON THE AGBR(100) SURFACE - FORMATION, ELECTRONIC-STRUCTURE AND SPECTRUM OF A PRIMARY AG2 CLUSTER

Ab initio calculations of the geometry, electronic structure, ionization and excitation energies of an M-center on the AgBr(100) surface are reported. This structure, formed in the process of surface reduction, may be viewed as an Ag2 molecule adsorbed on the AgBr(100) surface with a ''pit'' and may become a primary center for photographic latent image formation. We found the equilibrium position of the Ag2 molecule 0.62 angstrom above the surface and the adsorption energy 0.88 eV. The SIGMA(g)-->SIGMA(u) excitation energies are greater by 0.6-1.0 eV and ionization potentials are 1.3-1.8 eV less than those for the free molecule. The results of the calculations which do and do not treat Ag 4d electrons explicitly match each other well. The adsorption energy is compared with that in other ab initio Ag(n)/AgBr(100) calculations.