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WIREs Comput Mol Sci
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The empirical valence bond model: theory and applications

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Abstract Recent years have seen an explosion in computer power, allowing for the examination of ever more challenging problems. For instance, a recent simulation study, which was the first of its kind, was able to actually explore the dynamical nature of enzyme catalysis on a millisecond timescale (Pisliakov AV, Cao J, Kamerlin SCL, Warshel A. Proc Natl Acad Sci U S A 2009, 106:17359.), something that as recently as a year or two ago would have been considered impossible. However, the questions that need addressing are nevertheless very complex, and experimental approaches can unfortunately often be inconclusive (Åqvist J, Kolmodin K, Florián J, Warshel A, Chem Biol 1999, 6:R71.) in answering them. Therefore, it is essential to have an approach that is both reliable and able to capture complex systems in order to resolve long‐standing controversies [particularly with regards to questions such as the origin of enzyme catalysis, where the relevant energy contributions cannot be separated without some computational models (Warshel A, Sharma PK, Kato M, Xiang Y, Liu H, Olsson MHM, Chem Rev 2006, 106:3210.)]. Herein, we will present the empirical valence bond (EVB) approach, which, at present, is arguably the most powerful tool for examining chemical reactivity in the condensed phase. We will illustrate the effectiveness of the EVB method when evaluating, for instance, catalytic effects and demonstrate that it is currently the optimal tool for elucidating challenging problems such as understanding the catalytic power of enzymes. Finally, the increasing appreciation of this approach can maybe best illustrated not only by its proliferation but also by attempts to capture its basic chemistry under a different name, as will be discussed in this work. © 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 30–45 DOI: 10.1002/wcms.10 This article is categorized under: Electronic Structure Theory > Combined QM/MM Methods

A schematic description of the relationship between the free energy difference between the reactant and product states (ΔG0) and the activation free energy (Δg). This figure illustrates how shifting Δg2 by ΔΔG0 (which changes Δg2 to Δg2’ and ΔG0 to ΔG0 + ΔΔG0) changes Δg by a similar amount. This figure is adapted from Ref 126 (see also Ref 13). Note that the α in this figure corresponds to λ in the main text.

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An illustration of different models for reducing Δg. Here, either (a) ΔG12 is reduced while keeping the positions of the free energy functionals unchanged or (b) the minimum of Δg2 is shifted, thus changing the reorganization energy. This figure was originally presented in Ref 126.

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(a) The calculated relationship between Δg and ΔG0 for a series of SN2 reactions. (b) The dependence of the correlation coefficient dΔg/dΔG0 on ΔG0. This figure was originally presented in Ref 14.

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Electronic Structure Theory > Combined QM/MM Methods

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