Modelling water adsorption on Au(2 1 0) surfaces. I. A force field for water–Au interactions by DFT

A force field for the adsorption of water on Au(2 1 0) surfaces is presented, based on density functional theory (DFT) calculations of a single water molecule interacting with a gold cluster of 16 atoms, in a configuration representing the Au(2 1 0) crystal surface. Three gold atomic sites have been selected for the calculations: top (T), hollow1 (H1) and hollow2 (H2) located, respectively, at the first, second and third layers. The potential energy surface presents the typical behaviour of the water-noble metal interactions. The preferential adsorption on Au occurs at the T sites followed by the H1 and H2 ones, respectively. The preferential orientations at those sites show the water hydrogen atoms pointing outwards the metallic surface. An analytical function, fitted to the DFT results, has been developed. It expresses the interaction between the water atoms and the gold surface, considering its topography though not explicitly discriminating the orientation angles and the interactions with each of the gold atoms. They are implicitly taken into account by expanding the function as a linear combination of the water atoms interactions with the selected sites of gold. The coefficients of the linear combination are related to the periodicity of the macroscopic surface and assumed to approach the lateral variation of the corrugation energy. The proposed function has been used in Monte Carlo simulations of water adsorption on Au(2 1 0) surfaces whose results will be reported in another paper.