Atomic and molecular forms of oxygen on Ag(331). Theoretical analysis using the DFT method

Oxygen adsorption on Ag(331) is analyzed in a cluster approximation using t he density functional theory (DFT) method. Adsorption centers (AC) for the bridge (S2) and three-center (S3) coordinations of oxygen are identified on the stepwise face Ag(331) and the Ag-O bond energies at these centers are calculated. For atomic adsorption, the Ag-O bond strength varies from 50 to 65 kcal/mole, depending on AC.;The heat of molecular adsorption Delta H = 5 kcal/mole for S2(L1-L2) type AC. The molecule is oriented parallel to Ag( 110) between the terraces with R(O-O) = 1.34 Angstrom. Calculations showed that the ground state of the O-2/Ag20(331) system is a triplet, brit a part of spill density is delocalized on silver atoms, so that the spin density oil oxygen rho(s)(O) = 0.46 (rho(s) = 1.0 for the free O-2 molecule). The e nergy of the singlet state is 9 kcal/mole greater than that of the ground s tate.