On unjustifiably misrepresenting the EVB approach while simultaneously adopting it

Abstract

In recent years, the EVB has become a widely used tool in the QM/MM modeling of reactions in condensed phases and in biological systems, with ever increasing popularity. However, despite the fact that its power and validity have been repeatedly established since 1980, a recent work (Valero, R.; et al. J. Chem. Theory Comput. 2009, 5, 1) has strongly criticized this approach, while not discussing the fact that one of the authors is effectively using it himself for both gas-phase and solution studies. Here, we have responded to the most serious unjustified assertions of that paper, covering both the more problematic aspects of that work and the more complex scientific aspects. Additionally, we have demonstrated that the poor EVB results shown in Valero et al. which where presented as verification of the unreliability of the EVB model were in fact obtained by the use of incorrect parameters, without comparing to the correct surface obtained by our program.

Figure 1

Gas phase potential surfaces for proton transfer in the [HOHOH]^- ion, obtained using both ab initio (MP2/6-31G**, left) and EVB (right) approaches. All results are given in kcal/mol, relative to the R₀₀ minimum. This figure was originally presented in Ref. 12.

Figure 2

Contour plot of the ground-state adiabatic potential surfaces obtained by (a) EVB with a gas-phase shift of -23.0, (b) EVB with a gas-phase shift of +23.4.

Figure 3

(left) Diabatic and adiabatic FDFT energy profiles for the reaction, Cl^- + CH₃Cl → ClCH₃ + Cl^-, in the gas phase and in solution, where the reaction coordinate is defined as the energy difference between the diabatic surfaces, Δε = ε₁ - ε₂. (right) Plot of the H_ij of the reaction, Cl^- + CH₃Cl → ClCH₃ + Cl^-, both in the gas phase and in solution. The data are obtained from the diabatic and the adiabatic curves of Figure 1, using $H_{12}=\sqrt{({\epsilon }_1-E_g)\left({\epsilon }_2{-}_g\right)}$. These figures were originally presented in Ref. 7.

Figure 4

QM/MM activation free energies obtained by moving from the EVB to the QM/MM surfaces. This figure was originally presented in Ref. 24.

Figure 5

Contour plot of the ground-state adiabatic potential surfaces obtained by (a) EVB with a gas-phase shift of -23, (b) EVB with a gas-phase shift of +23.4 and (c) ab initio (B3LYP/6-311++G**). The reaction has been defined in terms of C-O (x-axis) and C-Cl (y-axis) distances. All energies are given relative to that of the reactant state, and all energies are given in kcal/mol.

Figure 6

Ground-state adiabatic potential energy profiles along the reaction coordinate obtained by (a) EVB, with a gas-phase shift of -23.0 (solid line), EVB with a gas-phase shift of +23.4 (dashed) and (c) B3LYP (dotted line). In each case, all energies are shown in kcal/mol relative to the ground state.

Figure 7

EVB energy profiles along the reaction coordinate for the DhlA model reaction in water, obtained using gas-phase shifts of -23.0 (left) and +23.4 (right), as well as the same EVB parameters as those presented in the supplementary material of Ref. 17. All energies are shown in kcal/mol.

Figure 8

EVB free energy profiles along the reaction coordinate for the DhlA model reaction in water, obtained using gas-phase shifts of -23.0 (left) and +23.4 (right), as well as the same EVB parameters as in the gas phase (i.e. those presented in the supplementary material of Ref. 17). All energies are shown in kcal/mol.