Ir15 (111) Cluster
N and NH adsorb at top, hexagonal close-packed, and face-centered cubic
positions using all methods – B3LYP, B3LYP-D3, and B97-D3. The HCP
position is most favored, closely followed by FCC. This is very similar
to the theoretical findings of Krekelberg et al., whose study used
periodic DFT methods PW91 and RPBE.38 They found that
HCP and FCC were equally favorable. NH2 adsorbs at the
bridge position for all methods and the top position for B3LYP-D3 and
B97-D3, with the bridge position being slightly more favorable.
NH3 also adsorbs at top and bridge positions for all
methods, and the top position is most favorable. This agrees with
Krekelberg’s theoretical findings, but is in conflict with an experiment
that found adsorption of NH3 at
FCC/HCP.38 Although for most of the molecules in this
study, more than one adsorption site is found possible, none of the
methods could find a minimum at the HCP or FCC position for
NH3.