Molecular mechanics models for the image charge, a comment on “including image charge effects in the molecular dynamics simulations of molecules on metal surfaces”

Self Cite

Modeling adsorption at the metal/water interfaces is a cornerstone towards an improved understanding in a variety of fields from heterogeneous catalysis to corrosion. We propose and validate a hybrid scheme that combines the adsorption free energies obtained in gas phase at the DFT level with the variation in solvation from the bulk phase to the interface evaluated using a molecular mechanics based alchemical transformation, denoted MMsolv. Using the GAL17 force field for the platinum/water interaction, we retrieve a qualitatively correct interaction energy of the water solvent at the interface. This interaction is of near chemisorption character and thus challenging, both for the alchemical transformation, but also for the fixed point-charge electrostatics. Our scheme passes through a state characterized by a well-behaved physisorption potential for the Pt(111)/H 2 O interaction to converge the free energy difference. The workflow is implemented in the freely available SolvHybrid package. We first assess the adsorption of a water molecule at the Pt/water interface, which turns out to be a stringent test. The intrinsic error of our QM-MM hybrid scheme is limited to 6 kcal/mol through the introduction of a correction term to attenuate the electrostatic interaction between near-chemisorbed water molecules and the underlying Pt atoms. Next, we show that the MMsolv solvation free energy of Pt (-0.46 J/m 2) is in good agreement with the experimental estimate (-0.32 J/m 2). Furthermore, we show that the entropy contribution at room temperature is roughly of equal magnitude as the free energy, but with opposite sign. Finally, we compute the adsorption energy of benzene and phenol at the Pt(111)/water interface, one of the rare systems for which experimental data are available. In qualitative agreement with experiment, but in stark contrast with a standard implicit solvent model, the adsorption of these aromatic molecules is strongly reduced (i.e., less exothermic by ~30 and 40 kcal/mol for our QM/MM hybrid scheme and experiment, respectively, but ~0 with the implicit solvent) at the solid/liquid compared to the solid/gas interface. This reduction is mainly due to the competition between the organic adsorbate and the solvent for adsorption on the metallic surface. The semi-quantitative agreement with experimental estimates for the adsorption energy of aromatic molecules thus validates the soundness of our hybrid QM-MM scheme. File list (2) download file view on ChemRxiv SolvHybrid.pdf (20.52 MiB) download file view on ChemRxiv SI-SolvHybrid.pdf (705.65 KiB)

Section: Theorymentioning

confidence: 99%

Solvation Free Energies and Adsorption Energies at the Metal/Water Interface from Hybrid Quantum-Mechanical/Molecular Mechanics Simulations

Clabaut

Schweitzer

Götz

et al. 2020

Self Cite

“…This non-polarizable 55 force field can be coupled to standard force fields and is compatible with any water-water interaction. However, GAL17 was developed having monometallic, perfectly flat single-crystal surfaces in mind.…”

Section: Introductionmentioning

confidence: 99%

Ten Facets, One Force Field: The GAL19 Force Field for Water–Noble Metal Interfaces

Clabaut

Fleurat‐Lessard

Michel

et al. 2020

Self Cite

Understanding the structure of the water/metal interfaces plays an important role in many are as ranging from surface chemistry to environmental processes. Due to their intrinsic complexity, the water/metal interfaces cannot yet be adequately described by quantum mechanical approaches and accurate force-fields are therefore needed. We develop and parametrize GAL19, a novel force-field to describe the interaction of water with two facets (111 and 100) of five metals (Pt, Pd, Au, Ag, Cu). To increase transferability compared to its predecessor GAL17, the water-metal interaction is described as a sum of pair-wise terms. The interaction energy has three contributions: (i) physisorption is described via a Tang and Toennies potential, (ii) chemisorption and surface corrugation relies on an attractive Gaussian term and (iii) the angular dependence is explicitly included as a truncated Fourier series. 13 parameters are used for each metal surface and were fitted on 250 water adsorption energies computed at the PBE+dDsC level. The performance of GAL19 was evaluated on a set of more than 600 DFT adsorption energies for each surface, leading to an average root mean square deviation (RMSD) of only 1 kcal/mol, correctly reproducing the adsorption trends: strong on Pt and Pd but weaker on Ag, Au and Cu. This force-field was then used to simulate the water/metal interface for all ten surfaces for 1 ns. Structural analyses reveal similar tendencies for all surfaces: a first, dense water layer that is mostly adsorbed on the metal top sites, and a second layer up to around 6 Å, which is less structured. On Pt and Pd, the first layer is strongly organized with water lying flat on the surface. The pairwise additive functional form allows to simulate the water adsorption on alloys, which is demonstrated at the example of Ag/Cu and Au/Pt alloys. The water/Ag-Cu interface is predicted to be disordered with water mostly adsorbed on Cu which should exacerbate the Ag reactivity. On the contrary, incorporating Pt into Au materials leads to a structuring of the water interface. Our promising results make GAL19 an ideal candidate to get representative sampling of complex metal/water interfaces as a first step towards accurate estimation of free energies of reactions in solution at the metal interface. File list (4) download file view on ChemRxiv GAL19-Unmarked.pdf (16.74 MiB) download file view on ChemRxiv GAL19-SI.pdf (4.42 MiB) download file view on ChemRxiv Datas.ods (20.44 KiB) download file view on ChemRxiv archive.zip (9.01 MiB)

“…This insight might help the development of more accurate Pt/H 2 O force fields. 68,69 The situation for H 2 S is more challenging to approximate: charge transfer dominates the interaction energy, which also induces significant deformations of the surface. Hence, already for H 2 S adsorption, explicit terms to mimic orbital/charge-transfer interactions are required.…”

Section: Resultsmentioning

confidence: 99%

Energy Decomposition Analysis for Metal Surface–Adsorbate Interactions by Block Localized Wave Functions

Staub

Iannuzzi

Khaliullin

et al. 2018

Self Cite

The energy decomposition analysis based on block localized wave functions (BLW-EDA) allows to gain physical insight into the nature of chemical bonding, decomposing the interaction energy in (1) a "frozen" term, accounting for the attraction due to electrostatic and dispersion interactions, modulated by Pauli repulsion, (2) the variationally assessed polarization energy and (3) the charge-transfer. This method has so far been applied to gas-and condensed-phase molecular systems. However, its standard version is not compatible with fractionally occupied orbitals (i.e. electronic smearing) and, as a consequence, cannot be applied to metallic surfaces. In this work, we propose a 1 simple and practical extension of BLW-EDA to fractionally occupied orbitals, termed Ensemble BLW-EDA. As illustrative examples, we have applied the developed method to analyze the nature of the interaction of various adsorbates on Pt(111), ranging from physisorbed water to strongly chemisorbed ethylene. Our results show that polarization and charge-transfer both contribute significantly at the adsorption minimum for all studied systems. The energy decomposition analysis provides details with respect to competing adsorption sites (e.g., CO on atop, vs. hollow sites) and elucidates the respective importance of polarization and charge transfer for the increased adsorption energy of H 2 S compared to H 2 O. Our development will enable a deeper understanding of the impact of charge transfer on catalytic processes in general.