title: Toward Accurate Adsorption Energetics on Clay Surfaces.
abstract: Clay minerals are ubiquitous in nature, and the manner in which they interact with their surroundings has important industrial and environmental implications. Consequently, a molecular-level understanding of the adsorption of molecules on clay surfaces is crucial. In this regard computer simulations play an important role, yet the accuracy of widely used empirical force fields (FF) and density functional theory (DFT) exchange-correlation functionals is often unclear in adsorption systems dominated by weak interactions. Herein we present results from quantum Monte Carlo (QMC) for water and methanol adsorption on the prototypical clay kaolinite. To the best of our knowledge, this is the first time QMC has been used to investigate adsorption at a complex, natural surface such as a clay. As well as being valuable in their own right, the QMC benchmarks obtained provide reference data against which the performance of cheaper DFT methods can be tested. Indeed using various DFT exchange-correlation functionals yields a very broad range of adsorption energies, and it is uncleara prioriwhich evaluation is better. QMC reveals that in the systems considered here it is essential to account for van der Waals (vdW) dispersion forces since this alters both the absolute and relative adsorption energies of water and methanol. We show, via FF simulations, that incorrect relative energies can lead to significant changes in the interfacial densities of water and methanol solutions at the kaolinite interface. Despite the clear improvements offered by the vdW-corrected and the vdW-inclusive functionals, absolute adsorption energies are often overestimated, suggesting that the treatment of vdW forces in DFT is not yet a solved problem.
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Zen
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Loïc M
authors.initials: LM
authors.lastname: Roch
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Cox
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Xiao Liang
authors.initials: XL
authors.lastname: Hu
authors.affiliation: SISSA-International School for Advanced Studies, Via Bonomea 26, 34136 Trieste, Italy; INFM Democritos National Simulation Center, 34151 Trieste, Italy.
authors.forename: Sandro
authors.initials: S
authors.lastname: Sorella
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Dario
authors.initials: D
authors.lastname: Alfè
authors.affiliation: Thomas Young Centre and London Centre for Nanotechnology, 17-19 Gordon Street, London WC1H 0AH, United Kingdom; Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Angelos
authors.initials: A
authors.lastname: Michaelides