Theoretical and Computational Chemistry

Proton Transfer in Bulk Water using the Full Adaptive QM/MM Method: Integration of Solute- and Solvent-Adaptive Approaches

Hiroshi C. Watanabe Keio University


The quantum mechanical/molecular mechanical (QM/MM) method is a hybrid molecular simulation technique that increases the accessibility of local electronic structures of large systems.
The technique combines the benefit of accuracy found in the QM method and that of cost efficiency found in the MM method.
However, it is difficult to directly apply the QM/MM method to the dynamics of solution systems, particularly for proton transfer.
As explained in the Grotthuss mechanism, proton transfer is a structural interconversion between hydronium ions and solvent water molecules.
Hence, when the QM/MM method is applied, an adaptive treatment, namely on-the-fly revisions on molecular definitions, is required for both the solute and solvent.
Although several solvent-adaptive methods have been proposed, a full adaptive framework, which is an approach that also considers adaptation for solutes, remains untapped. In this paper, we propose a new numerical expression for the coordinates of the excess proton and its control algorithm.
Furthermore, we confirm that this method can stably and accurately simulate proton transfer dynamics in bulk water.

Version notes

In the previous versions, there were bugs in the program for the calculation in derivative of the QM center. Hence, we modified it and recalculated all relevant data. According to it, we also rewrite discussions.


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Supplementary material

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20201210 SI.v3