For the SAMPL7 pK a challenge, participants were required to submit predictions ina novel format, reporting transition free energies between microstates as in the "Δ 0 " formalism outlined in Gunner et al. (and similar to the work of Selwa et al. ). Here, the pH-dependent free energy change between "states" and is defined by rewriting the well-known Henderson-Hasselbalch equation for, e.g., the general reaction (Eq. 3) in the form