A study of the reaction H + O2 ⇌ HO2 ⇌ O + OH at four levels of density-functional theory

The minimum-energy pathway and the energetics of the reaction H + O2 ⇌ HO2 ⇌ O + OH have been computed at four levels of density-functional theory, involving local and nonlocal exchange and correlation terms. The four exchange-correlation potentials produce very similar geometries for the HO2 intermediate, and similar trajectories for the reaction path in the neighborhood of HO2; the pathways begin to differ more significantly at greater distances between reactant or product species, as the surface flattens out toward the asymptotic dissociation energy. The experimental energetics are reproduced most accurately by nonlocal exchange plus local correlation. Addition of a nonlocal correlation term worsens the agreement.