We use a polarizable continuum approach to study the acidity of tert-butyl alcohol in water at ambient, near-critical, and supercritical conditions. In the most straightforward calculation, the bare ionic species (the tert-butoxy anion and the hydronium cation) are placed in cavities surrounded by a dielectric continuum, using a dielectric constant corresponding to the state point. A second method is first to solvate these ions with a small number of explicit water molecules and then surround this cluster with the dielectric. This is the cluster-continuum approach. We discuss the advantages and disadvantages of these two schemes and we also discuss various ways in which the second method can be implemented. No method showed quantitative agreement with all available experimental results but the first, straightforward method was the most successful in predicting the correct trends. From both a numerical and a theoretical point of view, we believe this is the method of choice.
(c) 2004 American Institute of Physics.