Using density-functional theory, we provide the first conclusive evidence o
f the existence of a molecularly chemisorbed state for oxygen on the Rh (11
1) surface. Four species are identified: a paramagnetic state above the bri
dge site with a binding energy of 1.95 eV, a more weakly bound paramagnetic
state above the top site with a binding energy of 0.95 eV, and two nonmagn
etic states above the face-centered-cubic (fcc) and hexagonal-close-packed
(hcp) hollow sites each with a binding energy of 1.98 eV. We compare these
results with our calculations of the binding energy for atomic oxygen on th
e fcc and hcp hollow sites and an upper bound on the dissociation barrier t
o understand major portions of the dissociation reaction coordinate. Combin
ing our data with the experimental and theoretical results for oxygen disso
ciation on many other fcc (111) metal surfaces, we conclude that all these
metal surfaces possess similar minima corresponding to physisorption, molec
ular chemisorption, and dissociative chemisorption. Despite these similarit
ies, the differing binding energies and barrier heights account for the var
ying mechanisms of oxygen dissociation on different fcc (111) surfaces. (C)
2000 American Institute of Physics. [S0021-9606(00)70633-7].