Wetting of water on hexagonal boron nitride@Rh(111): A QM/MM model based on atomic charges derived for nano-structured substrates

The wetting of water on corrugated and flat hexagonal boron nitride (h-BN) monolayers on Rh(111) is studied within a hybrid quantum mechanics/molecular mechanics (QM/MM) approach. Water is treated by QM methods, whereas the interactions between liquid and substrate are described at the MM level. The electrostatic properties of the substrate are reproduced by assigning specifically generated partial charges to each MM atom. We propose a method to determine restrained electrostatic potential (RESP) charges that can be applied to periodic systems. Our approach is based on the Gaussian and plane waves algorithm and allows an easy tuning of charges for nano-structured substrates. We have successfully applied it to reproduce the electrostatic potential of the corrugated and flat h-BN/Rh(111) known as nanomesh. Molecular dynamics simulations of water films in contact with these substrates are performed and structural and dynamic properties of the interfaces are analyzed. Based on this analysis and on the interaction energies between water film and substrate, we found that the corrugated nanomesh is slightly more hydrophilic. On a macroscopic scale, we expect a smaller contact angle for a droplet on the corrugated surface.