Precise and accurate determination of the pKw of heavy water via a new protocol within the Blue Moon ensemble: comparison to light water and implications for ab initio simulations

Water self-dissociation is one of the most studied reactions in aqueous medium, having received a special attention from the computational chemistry community. However, a precise and accurate in silico estimation of the pKw remained elusive for a long time, until very recent works finally reached this goal with a strong technical effort. In this work, I define a very accessible procedure within the Blue Moon ensemble approach that allows a precise determination of the pKw , correcting two effects present in the regular application of different constrained MD methods that caused a wrong description of the dissociated state. This approach, together with an extremely efficient ab initio setup within the Second-generation Car–Parrinello MD scheme, and a description of the electronic structure at the RPBE-D3 level, yields an estimation of the pKw of heavy water that is practically equal to the experimental value. The comparison of this result with the one in light water provides interesting conclusions, with important implications for the ab initio simulation of water.