Table 1. Fe–O694 Distance Determined by QM/MM Geometry Optimization of Ferrous SLO with QM-L Region and Various Functionals^a.

	without solvent			with solvent
	Min-5C	Min-6C	energy difference (kcal/mol)b	Min-5C	Min-6C
B3LYP	3.09	2.36	4.3	2.85	2.36
B3LYP-D3	3.35	2.36	–1.8	2.65	2.36
B3P86	3.24	2.36	4.7	2.93	2.36
M06-L	3.14	2.37	0.3	2.71	2.37

^aDistances are given in Å, and energies are given in kcal/mol. The initial coordinates were chosen to correspond to 5C or 6C geometries for the corresponding geometry optimizations. The QM region and the MM region including all residues within 20 Å of the Fe center were optimized simultaneously.

^bThe energy difference is the energy of the 6C minimum subtracted from the energy of the 5C minimum without solvent. Note that this energy difference corresponds to these two specific minima, but there are many related minima of each type with different energies on the potential energy surface. Because this energy difference does not include the effects of conformational sampling, it cannot be used to determine the relative populations of these two states. This energy difference is only given for the system without solvent because for the solvated system, the 5C and 6C systems have a slightly different number of solvent molecules due to the solvation procedure. Other local minima have different energies and span a range.