Diffusion quantum Monte Carlo calculation of the binding energy of positronium hydroxide

Using the diffusion quantum Monte Carlo method, the binding energy of positronium hydroxide (alternatively, the positronium affinity of the hydroxyl radical) has been calculated at a new level of accuracy and found to be 0.63+/-0.15 eV. Using the same methods, we also calculate the electron affinity of the hydroxyl radical to be 1.86+/-0.14 eV, which is in agreement with the experimental value. To the authors' knowledge, this is the only calculation of these quantities for which this essential consistency is demonstrated.