Structure and ultrafast dynamics of liquid water: A quantum mechanics/molecular mechanics molecular dynamics simulations study

Abstract

A quantum mechanics/molecular mechanics molecular dynamics simulation was performed for liquid water to investigate structural and dynamical properties of this peculiar liquid. The most important region containing a central reference molecule and all nearest surrounding molecules (first coordination shell) was treated by Hartree-Fock (HF), post-Hartree-Fock [second-order Moller-Plesset perturbation theory (MP2)], and hybrid density functional B3LYP [Becke's three parameter functional (B3) with the correlation functional of Lee, Yang, and Parr (LYP)] methods. In addition, another HF-level simulation (2HF) included the full second coordination shell. Site to site interactions between oxygen-oxygen, oxygen-hydrogen, and hydrogen-hydrogen atoms of all ab initio methods were compared to experimental data. The absence of a second peak and the appearance of a shoulder instead in the gO-O graph obtained from the 2HF simulation is notable, as this feature has been observed so far only for pressurized or heated water. Dynamical data show that the 2HF procedure compensates some of the deficiency of the HF one-shell simulation, reducing the difference between correlated (MP2) and HF results. B3LYP apparently leads to too rigid structures and thus to an artificial slow down of the dynamics.

Cluster Model for the Ionic Product of Water: Accuracy and Limitations of Common Density Functional Methods

“…[76][77][78] Another approach, applicable to liquid water molecular dynamics simulations, 79 is the use of a mixed quantum mechanics/ molecular mechanics (QM/MM) technique. Within this approach, the most important region containing the particles under investigation (i.e., both H 3 O + and OH -with their tight solvation shells) should be described either by the B3LYP functional or, if computationally feasible, by the RI-MP2 method, while the rest of the aqueous system is treated using an empirical force field.…”

A Combined QM/MM Molecular Dynamics Simulations Study of Nitrate Anion (NO3-) in Aqueous Solution

“…49 In this work, τ H2O (O i ) < τ H2O (H 2 O) results from both the HF/MM and B3LYP/MM simulations, without much differences in the values. However, as can be seen in Table 6, the previous B3LYP/MM simulation 43 of pure water had predicted much too slow exchange rates (while the HF values are close to the experimental values), proving the overestimation of hydrogen-bond strength by the B3LYP method. Hence, the anion-induced MRT differences obtained from the B3LYP/MM results are surely correct for the description but most probably too high in the amount.…”

“…These data are in good accord with a generally more rigid structure of hydrated NO 3 -resulting from the DFT approach, which generally tends to exaggerate the strength of hydrogen bonds. 42,43 3.…”

Absolute proton hydration free energy, surface potential of water, and redox potential of the hydrogen electrode from first principles: QM/MM MD free-energy simulations of sodium and potassium hydration

“…The QM/MM MD simulations rely on the quantum-mechanical charge field (QMCF) approach, 158,159 which belongs to the family of adaptive QM/MM methods 148,149,160 and has been applied with success in the past to investigations of solvated ions, 153,154 molecules, 161,162 coordination complexes, 163,164 and biomolecular systems. 165,166 Single-determinantal approaches such as ab initio HartreeFock 167,168 (HF) or DFT 169,170 have a limited accuracy/reliability 120,[123][124][125][126][127]155,[171][172][173][174][175][176] in the description of hydration phenomena. Thus, a correlated ab initio method is employed here to describe the QM subsystem (ion and first hydration shell), namely, resolution-of-identity secondorder Møller-Plesset perturbation 177,178 (RIMP2).…”