Dynamics and Energetics of Methane …
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3.3.4 Interaction Between Methane’s C–H Bond and IrO 2 Surface
Now that we have understood the origin of the peaks in the COOP curve for the
deformed methane molecule, which has the same structure as the one adsorbed on
the surface, we are ready to look into the interaction between the C–H bond and
the surface orbitals. First, the deformed CH 4 molecule is placed at the middle of the
vacuum slab on the IrO 2 (110) surface (see Fig. 15a), and then the COOP curve for
its C–H bond is calculated. The shape of the COOP spectrum is generally the same
as that shown in Fig. 13 because in this calculation there is no interaction between
the C–H bond and the surface, either. However, the location of the Fermi level is
different between the two calculations. In Fig. 13, the Fermi level is situated at the
same energy location as that of the HOMO of methane, while in the case of Fig. 15a
the Fermi level coincides with that of the IrO 2 surface slab. From this figure, it is clear
that the methane’s HOMOs are so close to the Fermi level that it would be reasonable
to assume they would become active orbitals for the adsorption of methane and the
following activation of its C–H bond.
In Fig. 15b is shown the COOP curve for the C–H bond of methane which is
strongly bound by the IrO 2 (110) surface. Comparing this COOP profile with that
shown in Fig. 15a, we see the peaks far from the Fermi level appear to remain
Fig. 15 COOP curve for the C–H bond of a deformed CH 4 molecule (highlighted by the red dashed
circle in the structure shown on the right-hand side of each COOP graph). In a the deformed CH 4
molecule is placed at the middle of the vacuum slab so that the interaction with the surface can be
negligible, while in b the methane-adsorbed structure is used for the COOP calculation. The energy
step size was set to 0.1 eV, the Gaussian smoothing was used with a standard deviation value of
0.2 eV, and a k-point sampling of 4 × 6 × 1 was used. The Fermi level (E F ) is set to zero (horizontal
dashed line)
121
3.3.4 Interaction Between Methane’s C–H Bond and IrO 2 Surface
Now that we have understood the origin of the peaks in the COOP curve for the
deformed methane molecule, which has the same structure as the one adsorbed on
the surface, we are ready to look into the interaction between the C–H bond and
the surface orbitals. First, the deformed CH 4 molecule is placed at the middle of the
vacuum slab on the IrO 2 (110) surface (see Fig. 15a), and then the COOP curve for
its C–H bond is calculated. The shape of the COOP spectrum is generally the same
as that shown in Fig. 13 because in this calculation there is no interaction between
the C–H bond and the surface, either. However, the location of the Fermi level is
different between the two calculations. In Fig. 13, the Fermi level is situated at the
same energy location as that of the HOMO of methane, while in the case of Fig. 15a
the Fermi level coincides with that of the IrO 2 surface slab. From this figure, it is clear
that the methane’s HOMOs are so close to the Fermi level that it would be reasonable
to assume they would become active orbitals for the adsorption of methane and the
following activation of its C–H bond.
In Fig. 15b is shown the COOP curve for the C–H bond of methane which is
strongly bound by the IrO 2 (110) surface. Comparing this COOP profile with that
shown in Fig. 15a, we see the peaks far from the Fermi level appear to remain
Fig. 15 COOP curve for the C–H bond of a deformed CH 4 molecule (highlighted by the red dashed
circle in the structure shown on the right-hand side of each COOP graph). In a the deformed CH 4
molecule is placed at the middle of the vacuum slab so that the interaction with the surface can be
negligible, while in b the methane-adsorbed structure is used for the COOP calculation. The energy
step size was set to 0.1 eV, the Gaussian smoothing was used with a standard deviation value of
0.2 eV, and a k-point sampling of 4 × 6 × 1 was used. The Fermi level (E F ) is set to zero (horizontal
dashed line)