Kusalik and co-workers have suggested that the hemibonded H 2 O • • • OH motif is an alternative structure that lies 2-3 kcal/mol higher in energy than the hydrogen-bonded structure HOH • • • OH, on the basis of semilocal DFT simulations using the same OH(H 2 O) 63 simulation cell that is employed here. Calculations on OH(H 2 O) 7 clusters at the level of second-order Møller-Plesset perturbation theory (MP2), where SIE is absent, also support the existence of hemibonded local minima. If the hemibonded configurations are indeed rare, and ), the same level of theory used to determine spin leakage in the previous QM/MM calculations. especially if the use of a hybrid functional reduces the O * • • • O distance relative to that obtained using semilocal functionals, then it is easy to see how a distinct hemibonding feature in g(r O * O ) might be hidden beneath the much larger hydrogen-bonded feature, especially in warmer water.