Electronic Polarizability and the Effective Pair Potentials of Water

Leontyev, Igor; Stuchebrukhov, Alexei A.

doi:10.1021/ct1002048

Cited by 103 publications

(148 citation statements)

References 27 publications

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“…In this respect, it is interesting to note that three recent approaches for improving the description of ion-water interactions at the MM level rely in effect on a weakening of the ion-solvent Coulombic interactions. These are: the induction-type 66,67,104,107,[278][279][280][281]284 force fields, where CT effects are included explicitly, the molecular dynamics in electric continuum (MDEC) approach, [285][286][287] where the ion charge is effectively scaled 75,[77][78][79]288 by a factor of about 0.7-0.9 (in line with QM results 282 ), and the multisite ion description, [289][290][291][292][293][294][295] where the ion charge is redistributed over virtual off-center sites within the ion. The observation made here that the features of the QM/MM RDFs can be reproduced more accurately with a MM model when reducing the nominal charge of the ion to +0.75 e is perfectly in line with these considerations.…”

Section: Discussionmentioning

confidence: 99%

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

Hofer

Hünenberger

2018

The Journal of Chemical Physics

104

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The absolute intrinsic hydration free energy G • H + ,wat of the proton, the surface electric potential jump χ • wat upon entering bulk water, and the absolute redox potential V • H + ,wat of the reference hydrogen electrode are cornerstone quantities for formulating single-ion thermodynamics on absolute scales. They can be easily calculated from each other but remain fundamentally elusive, i.e., they cannot be determined experimentally without invoking some extra-thermodynamic assumption (ETA). The Born model provides a natural framework to formulate such an assumption (Born ETA), as it automatically factors out the contribution of crossing the water surface from the hydration free energy. However, this model describes the short-range solvation inaccurately and relies on the choice of arbitrary ion-size parameters. In the present study, both shortcomings are alleviated by performing first-principle calculations of the hydration free energies of the sodium (Na + ) and potassium (K + ) ions. The calculations rely on thermodynamic integration based on quantum-mechanical molecular-mechanical (QM/MM) molecular dynamics (MD) simulations involving the ion and 2000 water molecules. The ion and its first hydration shell are described using a correlated ab initio method, namely resolution-of-identity second-order Møller-Plesset perturbation (RIMP2). The next hydration shells are described using the extended simple point charge water model (SPC/E). The hydration free energy is first calculated at the MM level and subsequently increased by a quantization term accounting for the transformation to a QM/MM description. It is also corrected for finite-size, approximate-electrostatics, and potentialsummation errors, as well as standard-state definition. These computationally intensive simulations provide accurate first-principle estimates for G • H + ,wat , χ • wat , and V • H + ,wat , reported with statistical errors based on a confidence interval of 99%. The values obtained from the independent Na + and K + simulations are in excellent agreement. In particular, the difference between the two hydration free energies, which is not an elusive quantity, is 73.9 ± 5.4 kJ mol 1 (K + minus Na + ), to be compared with the experimental value of 71.7 ± 2.8 kJ mol 1 . The calculated values of G • H + ,wat , χ • wat , and V • H + ,wat ( 1096.7 ± 6.1 kJ mol 1 , 0.10 ± 0.10 V, and 4.32 ± 0.06 V, respectively, averaging over the two ions) are also in remarkable agreement with the values recommended by Reif and Hünenberger based on a thorough analysis of the experimental literature ( 1100 ± 5 kJ mol 1 , 0.13 ± 0.10 V, and 4.28 ± 0.13 V, respectively). The QM/MM MD simulations are also shown to provide an accurate description of the hydration structure, dynamics, and energetics. Published by AIP Publishing.

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Section: Discussionmentioning

confidence: 99%

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

Hofer

Hünenberger

2018

The Journal of Chemical Physics

104

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“…In light of the arguments advanced in ref. [12][13][14][15], charge scaling would appear to be mandatory in models of ionic liquids without explicit polarization. In these systems, there is no high dielectric constant solvent to partially compensate for the effect of neglecting electronic polarization.…”

Section: Discussionmentioning

confidence: 99%

Solvation and ion-pairing properties of the aqueous sulfate anion: explicit versus effective electronic polarization

Pegado

Maršálek

Jungwirth

et al. 2012

Phys. Chem. Chem. Phys.

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We assessed the relative merits of two approaches for including polarization effects in classical force fields for the sulfate anion. One of the approaches is the explicit shell model for atomic polarization and the other is an implicit dielectric continuum representation of the electronic polarization, wherein the polarizability density is spatially uniform. Both the solvation and ion association properties of sulfate were considered. We carried out an ab initio molecular dynamics simulation for a single sulfate anion in aqueous solution to obtain a benchmark for the solvation structure. For the ion-pairing properties, the models were compared to experimental thermodynamic data through Kirkwood-Buff theory, which relates the integrals of the pair correlation functions to measurable properties. While deficiencies were found for both of the approaches, the continuum polarization model was not systematically worse than the shell model. The shell model was found to give a more structured solution than the continuum polarization model, both with respect to solvation and ion pairing.

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“…Leontyev and Stuchebrukhovaa. [106][107][108] suggested that to describe the PES of salt solutions, the charge of the ions should be scaled by 1/ √ ǫ ∞ (i.e 1 √ 1.8 = 0.75) . This is an interesting suggestion.…”

Section: Bmentioning

confidence: 99%

Water: one molecule, two surfaces, one mistake

Vega

2015

Molecular Physics

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In order to rigorously evaluate the energy and dipole moment of a certain configuration of molecules one needs to solve the Schrödinger equation. Repeating this for many different configurations allows one to determine the potential energy surface (PES) and the dipole moment surface (DMS). Since the early days of computer simulation it has been implicitly accepted that for empirical potentials the charges used to fit the PES should also be used to describe the DMS. This is a mistake. Partial charges are not observable magnitudes. They should be regarded as adjustable fitting parameters. Optimal values used to describe the PES are not necessarily the best to describe the DMS. One could use two fits: one for the PES, and another for the DMS. This is a common practice in the quantum chemistry community, but not used so often by the community performing computer simulations. This idea affects all types of modelling of water (with the exception of ab-initio calculations) from coarse grained to non-polarizable and polarizable models.We anticipate that an area that will benefit dramatically from having both, a good PES and a good DMS, is the modelling of water in the presence of electric fields.

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Electronic Polarizability and the Effective Pair Potentials of Water

Cited by 103 publications

References 27 publications

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

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

Solvation and ion-pairing properties of the aqueous sulfate anion: explicit versus effective electronic polarization

Water: one molecule, two surfaces, one mistake

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