Accelerated Computation of Free Energy Profile at Ab Initio QM/MM Accuracy via a Semi-Empirical Reference-Potential. IV. Adaptive QM/MM

In this work, we developed a novel adaptive QM/MM scheme and applied it to a study of the nucleophilic addition reaction. In this approach, the simulation was performed with a small QM region (without solvent molecules), and the thermodynamic properties under other potential energy functions with larger QM regions (with a different number of solvent molecules and/or different level of QM theory) are computed via the reference-potential method. The results show that this reweighting process is numerically stable, at least for the case studied in this work. Furthermore, this method also offers an inexpensive way to examine the convergence of the QM/MM calculation with respect to the size of the QM region.