Outlining the connection between the Δ 0 and the ST and PF formalisms is useful for practitioners who directly compute microstate free energies (including corresponding tautomerization free energies for which no pK a is defined) or microstate transition pK a values for single deprotonation reactions where a specific reaction direction is by definition implied. The general algorithm is as follows, with subscript order p , implying the reaction → -+ H + for any total charge on and subscript order Δ 0 meaning the reaction (+ H + ) → (+ H + ) with neutral . For all states not equal to the neutral reference microstate we have