Becke-Johnson damping, which was included to account for long-range van der Waals interactions. ωB97X-D has previously been shown to be able to reproduce geometries and energetics calculated using ab initio wavefunction methods, unlike other common density-functional approximations which do not predict stable gas-phase enolate intermediates. Some wavefunction calculations were also performed, where geometries were optimized using second-order Møller-Plesset perturbation theory (MP2), and subsequent coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] calculations were performed on the MP2-optimized geometries; this method is henceforth denoted as CCSD(T)@MP2.