Ir15 (100) Cluster
N adsorbs at the top and bridge positions for all methods and for
B97-D3, the hollow position as well; however, the bridge position is the
most favorable across all methods. For NH, B3LYP-D3 does not converge to
a bridge site, but B3LYP and B97-D3 do. B97-D3 shows an additional, less
favorable adsorption at the top position. Both B3LYP and B3LYP-D3
converged to hollow sites located only at the edges of the surface. Due
to edge effects on this hollow site, it is likely that bridge is the
most favorable site for NH. This is in agreement with adsorption of
monatomic O on Ir(100), which also has two unpaired electrons and
adsorbs at the bridge position.39 NH2and NH3 have only one favorable site – bridge and top
respectively.
Overall, all methods yield the same preferential adsorption sites on
both the (100) and (111) surfaces, with the exception of NH on (100).
B3LYP always gives the smallest binding energies, while its
dispersion-corrected form gives larger binding energies and B97-D3 gives
the largest binding energies.