Transferable Gaussian Attractive Potentials for Organic/Oxide Interfaces

Abstract

Organic/oxide interfaces play an important role in many areas of chemistry, and in particular for lubrication and corrosion. Molecular dynamics simulations are the method of choice for providing complementary insight to experiments. However, the force fields used to simulate the interaction between molecules and oxide surfaces tend to capture only weak physisorption interactions, discarding the stabilizing Lewis acid/base interactions. We here propose a simple complement to the straightforward molecular mechanics description based on "out-of-the-box" Lennard-Jones potentials and electrostatic interactions: the addition of an attractive Gaussian potential between reactive sites of the surface and heteroatoms of adsorbed organic molecules, leading to the GLJ potential. The interactions of four oxygenated and four amine molecules with the typical and widespread hematite and γ-alumina surfaces are investigated. The total RMSD for all probed molecules is only 5.7 kcal/mol, and the corresponding percentage 23% over hematite, while on γ-alumina the RMSD is 11.2 kcal/mol, despite using a single parameter for all five chemically inequivalent surface aluminum atoms. Applying GLJ to the simulation of organic films on oxide surfaces demonstrates that mobility of the surfactants is overestimated by the simplistic LJ potential, while GLJ and other qualitatively correct potentials show a strong structuration and slow dynamics of the surface films, as could be expected from the first-principles adsorption energies for model head-groups.

An Electrostatically Embedded QM/MM Scheme for Electrified Interfaces

“…Instead of system-specific tuning of parameters, several research groups have pushed for hybrid solvation schemes, where the (surface) reactions are described at the density functional theory (DFT) level and the solvent effects are captured by molecular mechanics (MM). − MM is many orders of magnitude less expensive than DFT, and therefore, extensive phase-space sampling of the liquid is easily in reach. Furthermore, compared to implicit solvents, it is clearer how to improve the quality of the description of the interface energetics: Force fields can be tested against DFT and system-specifically improved. , As an example, we have shown that a purpose-built force field for the interaction of water with the Pt(111) surface leads to a semiquantitative agreement with experiment for the adsorption of phenol and benzene on Pt(111), while the standard implicit solvent gives qualitatively wrong results when comparing the adsorption in the gas phase with adsorption in the liquid . Similarly, good agreement between DFT and MM solvation energies has been achieved at the alumina/water interface .…”

The application of QM/MM simulations in heterogeneous catalysis

“…Alternatively, MM atoms at the QM/MM boundary can be replaced by pseudopotentials 32 . However, parameterising force-fields to match the energetics of the QM and MM regions more reliably reduces the energetic discontinuity without introducing additional corrective potentials [43][44][45] .…”

“…31 However, parameterising force-fields to match the energetics of the QM and MM regions more reliably reduces the energetic discontinuity without introducing additional corrective potentials. 42–44…”

“…31 However, parameterising forcefields to match the energetics of the QM and MM regions more reliably reduces the energetic discontinuity without introducing additional corrective potentials. [42][43][44] There are numerous strategies for selecting force-fields to satisfy the above conditions. Many studies transfer an optimised force-field designed to minimise the error of observables relative to experiment; however, this approach may lead to energetic and structural discontinuity between the classical and quantum regions, especially if the QM method deviates from the empirical structure.…”

How to Gain Atomistic Insights on Reactions at the Water/Solid Interface?

“…This MMSolv strategy has been validated against experimental data on the adsorption of aromatics at the Pt/water interface. − MMSolv performs noticeably better than PCM thanks to a proper inclusion of the surface solvation. It can be easily used with oxides surfaces, given that the chemisorption of water is well described . When considering the adsorption of flexible molecules (e.g., polyols), MMsolv can be combined with our package DockOnSurf to automate the sampling of conformers.…”