A theoretical study of the H2O-Au(1 1 1) interface based on first principles density functional theory
(DFT) calculations with and without inclusion of dispersion correction is reported. Three different computational approaches are considered. First, the standard generalized gradient approximation
(GGA) functional PBE is employed. Second, an additional energy term is further included that adds
a semi-empirically derived dispersion correction (PBE-D2), and, finally, a recently proposed functional that includes van der Waals (vdW) interactions directly in its functional form (optB86b-vdW)
was used to represent the state-of-the art of DFT functionals. The monomeric water adsorption was
first considered in order to explore the dependency of geometry on the details of the model slab
used to represent it (size, thickness, coverage). When the dispersion corrections are included the
Au-H2O interaction is stronger, as manifested by the smaller dAu-O and stronger adsorption energies. Additionally, the interfacial region between Au(1 1 1) slab surfaces and a liquid water layer
was investigated with Born-Oppenheimer molecular dynamics (BOMD) using the same functionals.
Two or three interfacial orientations can be determined, depending on the theoretical methodology
applied. Closest to the surface, H2O is adsorbed O-down, whereas further away it is oriented with
one OH bond pointing to the surface and the molecular plane parallel to the normal direction. For the
optB86b-vdW functional a third orientation is found where one H atom points into the bulk water
layer and the second OH bond is oriented parallel to the metal surface. As for the water density in the
first adsorption layer we find a very small increase of roughly 8%. From the analysis of vibrational
spectra a weakening of the H-bond network is observed upon the inclusion of the Au(1 1 1) slab,
however, no disruption of H-bonds is observed. While the PBE and PBE-D2 spectra are very similar, the optB86b-vdW spectrum shows that the H-bonds are even more weakened.Ministerio de Ciencia e Innovación de España-MAT2012-31526 y CSD2008-002
