Table 5.

Structural Parameters and Relative Energies for the Model Iron–Hydroperoxo Intermediate in Different Spin States, from DFT Calculations at the PBE, $\text{PBE}+U$, and B3LYP Levels

method		spin state	$d_{\text{Fe-proximal O}}$ (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.$	1.67	1.91	129.8	4.11
		$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	1.99	1.47	124.8	0.00
$\text{PBE}+U$		$S=\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.18	1.44	122.2	0.60
		$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.11	1.47	121.8	0.00
B3LYP		$S=\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	1.91	1.47	123.9	8.00
		$S=\raisebox{1ex}{$5$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$	2.00	1.47	123.9	0.00
expt21			2.00		126