3 Å is usually equated with the presence or absence of hemibonding, and this feature vanishes when semilocal functionals are replaced by hybrids, or when a self-interaction correction is introduced. The QM/ MM results are more ambiguous and reveal that the feature at small r O * O is quite sensitive to the fraction of exact exchange, diminishing in prominence when BLYP is replaced by functionals such as B3LYP or PBE0, and vanishing altogether for the BH&HLYP functional that contains 50% exact exchange. On the other hand, while our QM/MM simulations used a very large periodic simulation cell (1,024 water molecules), the QM region was limited to OH(H 2 O) 31 and the simulation timescale was restricted to < 5 ps, because exchange of QM and MM water molecules in the cybotactic region takes place on a timescale of only a few picoseconds. While the prevailing viewpoint in the literature is that the hemibonded solvation motif is an artifact, calculations on small OH(H 2 O) n clusters suggest that that hemibonded configurations are needed to explain the electronic absorption spectrum of OH(aq). The band maximum of that spectrum of appears at 230 nm (5.4 eV), which constitutes an enormous blueshift compared to the Ã 2 Σ + ← X 2 Π transition of gasphase OH, which appears at 307 nm (4.0 eV). It is suggested that the 230 nm transition does not involve the Ã 2 Σ + state of the radical at all, but instead arises due to an intense 1b 2 (H 2 O) → 2p( OH) charge-transfer transition, specifically associated with hemibonded con- figurations. Our QM/MM simulations seemed to confirm this mechanism. In summary, the situation is that scant attention has been paid to hemibonded configurations in condensed-phase ai MD simulations, because they were thought to be artifacts, yet these "artifacts" (or perhaps rare events or a minority population) seem to be necessary to reproduce the ultraviolet (UV) spectroscopy of OH(aq).