Dynamics and Energetics of Methane …
125
Large positive and negative peaks can be found just below and above the Fermi level,
respectively, which is a signature of a strong, attractive interaction. The interaction
between the 2p z orbital of C and the 6p z orbital of Ir is also found important (see
Fig. 19c), but the 6p z orbital is located higher in energy, and so the interaction mainly
happens in a region way above the Fermi level. However, one should notice that these
orbitals appear to mix into the orbitals generated from the interaction between the
2p z orbital of C and the 5d z2 orbital of Ir in a second-order fashion. One may wonder
if the interaction between C
s 2p x and Ir
s 5d xz or between C
s 2p y and Ir
s 5d yz would
be of importance. In fact, we have checked them, and found that their contribution
to the total COOP curve is almost a half of the C(2p z )-Ir(5d z2 ) and C(2p z )-Ir(6p z )
contributions.
An alternative way to probe the interaction between the σ CH orbital and the surface
Ir orbitals is to take a look at the COOP profile calculated for the pair of the Ir and H
atoms (see Fig. 20a). This COOP curve looks similar to the one for the C–Ir COOP
curve. We observe positive bonding peaks in a range from −3 eV to −5 eV, while
the anti-bonding counterpart can be found at around E = 2 eV. The decomposition of
the total COOP curve into the atomic-orbital contributions, as shown in Fig. 20b–d,
reveals that the main contributor is the interaction between H
s 1s and Ir
s 6p z orbitals,
yet their contribution is a second-order manner. Also, the contributions from Ir
s 5d z2
and 5d yz orbitals are found important, as can be rationalized by the schematic drawing
of the orbital interaction pattern depicted above each COOP plot.
Fig. 20 a COOP curve calculated for the H atom of methane and the Ir atom on the surface. The
H–Ir COOP profile is decomposed into the contributions from the interaction between H s 1s and
Ir s 6p z orbitals (b), the one between H s 1s and Ir s 5d z2 orbitals (c), and the one between H s 1s
and Ir s 5d yz orbitals
125
Large positive and negative peaks can be found just below and above the Fermi level,
respectively, which is a signature of a strong, attractive interaction. The interaction
between the 2p z orbital of C and the 6p z orbital of Ir is also found important (see
Fig. 19c), but the 6p z orbital is located higher in energy, and so the interaction mainly
happens in a region way above the Fermi level. However, one should notice that these
orbitals appear to mix into the orbitals generated from the interaction between the
2p z orbital of C and the 5d z2 orbital of Ir in a second-order fashion. One may wonder
if the interaction between C
s 2p x and Ir
s 5d xz or between C
s 2p y and Ir
s 5d yz would
be of importance. In fact, we have checked them, and found that their contribution
to the total COOP curve is almost a half of the C(2p z )-Ir(5d z2 ) and C(2p z )-Ir(6p z )
contributions.
An alternative way to probe the interaction between the σ CH orbital and the surface
Ir orbitals is to take a look at the COOP profile calculated for the pair of the Ir and H
atoms (see Fig. 20a). This COOP curve looks similar to the one for the C–Ir COOP
curve. We observe positive bonding peaks in a range from −3 eV to −5 eV, while
the anti-bonding counterpart can be found at around E = 2 eV. The decomposition of
the total COOP curve into the atomic-orbital contributions, as shown in Fig. 20b–d,
reveals that the main contributor is the interaction between H
s 1s and Ir
s 6p z orbitals,
yet their contribution is a second-order manner. Also, the contributions from Ir
s 5d z2
and 5d yz orbitals are found important, as can be rationalized by the schematic drawing
of the orbital interaction pattern depicted above each COOP plot.
Fig. 20 a COOP curve calculated for the H atom of methane and the Ir atom on the surface. The
H–Ir COOP profile is decomposed into the contributions from the interaction between H s 1s and
Ir s 6p z orbitals (b), the one between H s 1s and Ir s 5d z2 orbitals (c), and the one between H s 1s
and Ir s 5d yz orbitals