Using Ar adsorption to estimate the van der Waals contribution to the wetting of Ru(0001)

With a polarizability close to the mean for an H2O molecule, and a heat of adsorption on Ru(0001) known roughly from scattering experiments, an Ar atom is used as an H2O-surrogate in an effort to quantify the error incurred by poor treatment of van der Waals attraction in Generalized Gradient Approximation (GGA) studies of Ru wetting. The PW91-GGA underestimates the energy of an Ar atom 3.3 A above a Ru by similar to 85 meV. This is too small to alter the earlier, theoretical conclusion that an intact-molecule wetting layer on Ru(0001) is unfavorable compared to a partially dissociated one.