Perspective: How good is DFT for water?

Gillan, M. J.; Alfè, Dario; Michaelides, Angelos

doi:10.1063/1.4944633

Cited by 657 publications

(717 citation statements)

References 336 publications

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“…We attribute our more ordered structure to the dispersion interactions included in the present work and emphasize how long-range interactions are crucial to capture the full hydration structure of inorganic interfaces at ambient conditions. 104 The thickest hydration layer, 12 Å, is found for anatase (100). The intensity of the first density peak (at 2.2 Å) is almost twice that of anatase (101) and with no close neighbor peak.…”

Section: Hard and Soft Hydration Layersmentioning

confidence: 98%

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Agosta

Brandt

Lyubartsev

2017

The Journal of Chemical Physics

103

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Ab initio molecular dynamics simulations are reported for water-embedded TiO2 surfaces to determine the diffusive and reactive behavior at full hydration. A three-domain model is developed for six surfaces [rutile (110), (100), and (001), and anatase (101), (100), and (001)] which describes waters as “hard” (irreversibly bound to the surface), “soft” (with reduced mobility but orientation freedom near the surface), or “bulk.” The model explains previous experimental data and provides a detailed picture of water diffusion near TiO2 surfaces. Water reactivity is analyzed with a graph-theoretic approach that reveals a number of reaction pathways on TiO2 which occur at full hydration, in addition to direct water splitting. Hydronium (H3O+) is identified to be a key intermediate state, which facilitates water dissociation by proton hopping between intact and dissociated waters near the surfaces. These discoveries significantly improve the understanding of nanoscale water dynamics and reactivity at TiO2 interfaces under ambient conditions.

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Section: Hard and Soft Hydration Layersmentioning

confidence: 98%

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Agosta

Brandt

Lyubartsev

2017

The Journal of Chemical Physics

103

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“…Of the various methods available, diffusion Monte Carlo (DMC) is particularly attractive [18][19][20][21][22][23][24]. First, DMC has already been shown to offer the requisite accuracy for bulk ice phases by producing results in excellent agreement with experiment [11,12,25,26]. Second, owing to recent improvements in computational efficiency [27], it is now possible to obtain converged results on the large unit cells that must be considered when treating 2D ice with a many-body electronic structure approach.…”

Section: Published By the American Physical Society Under The Terms Omentioning

confidence: 99%

Evidence for stable square ice from quantum Monte Carlo

et al. 2016

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Recent experiments on ice formed by water under nanoconfinement provide evidence for a two-dimensional (2D) "square ice" phase. However, the interpretation of the experiments has been questioned and the stability of square ice has become a matter of debate. Partially this is because the simulation approaches employed so far (force fields and density functional theory) struggle to accurately describe the very small energy differences between the relevant phases. Here we report a study of 2D ice using an accurate wave-function based electronic structure approach, namely diffusion Monte Carlo (DMC). We find that at relatively high pressure, square ice is indeed the lowest enthalpy phase examined, supporting the initial experimental claim. Moreover, at lower pressures, a "pentagonal ice" phase (not yet observed experimentally) has the lowest enthalpy, and at ambient pressure, the "pentagonal ice" phase is degenerate with a "hexagonal ice" phase. Our DMC results also allow us to evaluate the accuracy of various density functional theory exchange-correlation functionals and force field models, and in doing so we extend the understanding of how such methodologies perform to challenging 2D structures presenting dangling hydrogen bonds. DOI: 10.1103/PhysRevB.94.220102 Recent transmission electron microscopy (TEM) measurements and classical molecular dynamics simulations report that a new two-dimensional (2D) square phase of ice forms [1]. This phase is not part of the bulk ice phase diagram, but it was suggested that it is stabilized under confinement because of lateral pressure, estimated to be in the gigapascal (GPa), arising from the van der Waals (vdW) attraction between the graphene sheets. However, these experiments have been questioned [2], with it even being suggested that it is sodium chloride contamination and not ice that is responsible for the square symmetry observed. So far, it is not clear under what conditions (if any) square ice is stable.Theoretical investigations of the stability of confined 2D ice at high lateral pressures can, in principle, help in disentangling this issue and in complementing experimental findings [3][4][5][6][7][8][9][10]. From a theoretical perspective, the prediction of square 2D ice can be traced back to Nagle's 1970's "unit model" of ice [3]. However, later atomistic force field (FF) simulations found that 2D ice prefers a buckled rhombic structure [4,5]. More recently, density functional theory (DFT) based investigations [6-9] have been performed. However, these have produced qualitatively different results depending on the precise details of the calculations and, in particular, on the choice of exchange-correlation (XC) functional. For instance, Chen et al. [7] found hexagonal and pentagonal structures to be stable phases at low pressures (Fig. 1). They also found that square ice is only stable in the GPa pressure * angelos.michaelides@ucl.ac.uk Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further...

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“…For the cluster-continuum calculations, error sources include the selection of the clusters (sampling), their small sizes (smooth trends and fast convergence being required for a meaningful extrapolation 117 ), the estimation of the cluster entropy, 118-120 the choice of a cluster permittivity in the CE calculation, and the problems associated with a QM-CE boundary (surface definition, atomic radii). For the CPMD/BOMD calculations, error sources include the shortcomings of DFT methods in terms of electron correlation (including dispersion), affecting both bulk water properties [121][122][123][124][125][126][127][128][129][130] and ion-water interactions, 66,67,105,131 the small system sizes considered (resulting in a high weight for the approximate finite-size correction term), the very limited sampling times, the ambiguity in defining the appropriate reference potential within DFT water, 21,112,[132][133][134][135][136] and the numerical problems (see, e.g., footnotes 42 and 45 in Ref. 111) associated with creating a species or injecting electrons when applying computational alchemy in a QM framework [137][138][139][140][141][142][143] (see, however, Refs.…”

Section: Introductionmentioning

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

103

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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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Perspective: How good is DFT for water?

Cited by 657 publications

References 336 publications

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics

Evidence for stable square ice from quantum Monte Carlo

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

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