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Al-Hamdani Y.S.,Thomas Young Center and London Center for Nanotechnology | Al-Hamdani Y.S.,University College London | Ma M.,Thomas Young Center and London Center for Nanotechnology | Ma M.,University College London | And 6 more authors.
Journal of Chemical Physics | Year: 2015

Despite a recent flurry of experimental and simulation studies, an accurate estimate of the interaction strength of water molecules with hexagonal boron nitride is lacking. Here, we report quantum Monte Carlo results for the adsorption of a water monomer on a periodic hexagonal boron nitride sheet, which yield a water monomer interaction energy of -84 ± 5 meV. We use the results to evaluate the performance of several widely used density functional theory (DFT) exchange correlation functionals and find that they all deviate substantially. Differences in interaction energies between different adsorption sites are however better reproduced by DFT. © 2015 Author(s).

Cox S.J.,Thomas Young Center and London Center for Nanotechnology | Cox S.J.,University College London | Towler M.D.,University College London | Towler M.D.,University of Cambridge | And 4 more authors.
Journal of Chemical Physics | Year: 2014

High quality reference data from diffusion Monte Carlo calculations are presented for bulk sI methane hydrate, a complex crystal exhibiting both hydrogen-bond and dispersion dominated interactions. The performance of some commonly used exchange-correlation functionals and all-atom point charge force fields is evaluated. Our results show that none of the exchange-correlation functionals tested are sufficient to describe both the energetics and the structure of methane hydrate accurately, while the point charge force fields perform badly in their description of the cohesive energy but fair well for the dissociation energetics. By comparing to ice Ih, we show that a good prediction of the volume and cohesive energies for the hydrate relies primarily on an accurate description of the hydrogen bonded water framework, but that to correctly predict stability of the hydrate with respect to dissociation to ice Ih and methane gas, accuracy in the water-methane interaction is also required. Our results highlight the difficulty that density functional theory faces in describing both the hydrogen bonded water framework and the dispersion bound methane. © 2014 Author(s).

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