CCSD(T) Calculations. CCSD(T) calculations were performed on H 2 O, O 2 , and H 2 as well as atomic O and H in order to benchmark density functional performance for the overall oxygen reduction reaction. All calculations used B2PLYP geometries, a UHF reference, and a cc-pv6z basis. For free energy evaluations, the ZPE, thermal, and entropic corrections were taken from B2PLYP calculations.