Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001)

Abstract

In this work, a range of van der Waals type density functionals are applied to the HO/NaCl(001) and HO/MgO(001) interface systems to explore the effect of an explicit dispersion treatment. The functionals we use are the self-consistent vdW functionals vdW-DF, vdW-DF2, optPBE-vdW, optB88-vdW, optB86b-vdW, and vdW-DF-cx, as well as the dispersion-corrected PBE-TS and PBE-D2 methods; they are all compared with the standard PBE functional. For both NaCl(001) and MgO(001), we find that the dispersion-flavoured functionals stabilize the water-surface interface by approximately 20%-40% compared to the PBE results. For NaCl(001), where the water molecules remain intact for all overlayers, the dominant contribution to the adsorption energy from "density functional theory dispersion" stems from the water-surface interactions rather than the water-water interactions. The optPBE-vdW and vdW-DF-cx functionals yield adsorption energies in good agreement with available experimental values for both NaCl and MgO. To probe the strengths of the perturbations of the adsorbed water molecules, we also calculated water dipole moments and found an increase up to 85% for water at the MgO(001) surface and 70% at the NaCl(001) surface, compared to the gas-phase dipole moment.

Origins of fast diffusion of water dimers on surfaces

“…We first consider water monomer and dimer adsorption on the various substrates. The stable adsorption structures identified here agree with those observed in previous studies [20][21][22]25,27,[37][38][39][40][41] . Key structural information is provided in Table 1.…”

“…We base our diffusion mechanism discussions on the minimum energy pathway with the lowest barrier, and examples of the other translation pathways are shown in Supplementary Note 5. For water monomer diffusion on non-metal surfaces we find that on NaCl and MgO surfaces, monomers diffuse to adjacent top sites of metal ions through a hopping mechanism over the bridge site, as reported in previous studies 15,41,43 ; and on ZnO(1010), water monomers diffuse along the trenches on the surface, similar to what was found on TiO 2 14 .…”

“…1c. Some of the processes have been examined before with similar computational methods 16,37,41,49,50 and whenever comparison to previous works is possible, the agreement is reasonable despite differences in exchange-correlation functional between this and earlier studies. Our predicted monomer diffusion barriers on Pd(111) and NaCl(100) are in quantitative agreement with previous experiments 11,15 , as are our monomer and dimer barriers on Cu (111) 13 .…”

Adsorption of atmospheric gases on cementite 010 surfaces

“…20,21 Inclusion of van der Waals corrections leads to a significant increase in the surface energies of all terminations considered, as observed in calculations performed for surfaces of other systems like NaCl or MgO. 28 However, the energy differences between different slabs are comparable to the plain PBE values, and the relative order of stability of stoichiometric surfaces is similar to that found in other calculations, with the exception of the {001} and {111} terminations: the van der Waals-corrected calculation places the {111} surface energy slightly below that of the {001} surface, while plain GGA results find the opposite order. Nonetheless, in agreement with Zhao et al, 22 we also find that the {010} surface becomes more stable at a wide range of chemical potentials if one considers a nonstoichiometric slab created by removing two atom layers from the top and bottom of the slab.…”

Multi-Scale Modelling of Water and Hydroxide in Solids and Solutions

“…Using a range of dispersion-corrected DFT functionals and water coverages, we recently studied water on the archetypical NaCl(001) and MgO(001) surfaces [10], and found that, for both NaCl(001) and MgO(001), the dispersion-flavored functionals stabilize the water-surface interface by 20%-40% compared to the PBE-results. A monolayer water coverage on MgO(001) leads to a mixed overlayer with both intact and dissociated water molecules in an intricate hydrogen-bonded scheme.…”