Table 3.

Structure and Energetics of a Larger Model System Including the Histidine Beta Carbons^a

method	spin state	$d_{\text{Fe}-\text{S}}$ (Å)	$d_{\text{Fe}-\text{proximal O}}$ (Å)	$d_{\text{O}-\text{O}}$ (Å)	${\angle }_{\text{Fe}-\text{O}-\text{O}}$ (deg)	energy (kcal/mol)
PBE	$S=\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.40	1.83	1.39	126.3	−0.35
	$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.56	1.84	1.37	155.9	0.00
$\text{PBE}+U$	$S=\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.58	2.26	1.35	125.7	−0.41
	$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.56	2.31	1.35	125.9	0.00
B3LYPb	$S=\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.51	2.12	1.34	127.3	−0.82
	$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.50	2.27	1.34	128.6	0.00

^aHistidine beta carbons were kept fixed during geometry optimization, while all the other atoms are allowed to relax.

^bIn the B3LYP calculations, the 6–31+G* and 6–31G* atomic basis sets are used for the superoxide radical anion and the remaining atoms, respectively.