We calculated the adsorption energy of CH4 at the iron-oxo site MO to be -8.7 kJ/mol, of which 87% is contributed by dispersion interactions (PBE level of theory). See Figure for an energy diagram of the PBE and HSE06 relative energies. No energy barrier is observed for the adsorption in an NEB calculation tracking the movement of CH4 from the center of the pore to the iron-oxo site MO (see Figure ). Based on previous work, we initially hypothesized that a CH3 radical near the Fe(OH)2 site would be a local minimum on the potential energy surface after the C-H bond activation and therefore chose such a structure as a starting point for a geometry optimization. This optimization of CH3@Fe(OH)2 resulted in a CH3 radical structure at the Fe(OH)2 site with forces below the convergence criterion of 0.02 eV/Å, as expected, but a climbing image NEB calculation (Figure ) showed no transition state between the starting CH4@MO structure and the resulting CH3@Fe(OH)2 radical structure. Subsequent partial vibrational analysis (Fe and connected OH and CH3) revealed one low frequency imaginary mode of 27.4i cm -1 as shown in Figure , indicating that this species is a transition state ( 1 TS CH ) rather than the expected intermediate. The CH3 species in 1 TS CH is weakly physisorbed with a binding energy of -10.1 kJ/mol (HSE06; for PBE -11.3 kJ/mol) at the Fe(OH)2 site. Of this binding energy, 71% (65% for PBE) of the adsorption energy is contributed by dispersion interactions.