Influence of Coupling and Embedding Schemes on QM Size Convergence in QM/MM Approaches for the Example of a Proton Transfer in DNA

J. Chem. Theory Comput., 2017, 13 (3), pp 1102–1107, DOI: 10.1021/acs.jctc.6b00727
J. Chem. Theory Comput., online article

The influence of embedding and coupling schemes on the convergence of the QM size in the QM/MM approach is investigated for the transfer of a proton in a DNA base pair. We find that the embedding scheme (mechanical or electrostatic) has a much greater impact on the convergence behavior than the coupling scheme (additive QM/MM or subtractive ONIOM). To achieve size convergence, QM regions with up to 6000 atoms are necessary for pure QM or mechanical embedding. In contrast, electrostatic embedding converges faster: for the example of the transfer of a proton between DNA base pairs, we recommend including at least five base pairs and 5 Å of solvent (including counterions) into the QM region, i.e., a total of 1150 atoms.

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