Surface Adsorption from the Exchange-Hole Dipole Moment Dispersion Model

The accurate calculation
of intermolecular interaction energies
with density functional theory requires methods that include a treatment
of long-range, nonlocal dispersion correlation. In this work, we explore
the ability of the exchange-hole dipole moment (XDM) dispersion correction
to model molecular surface adsorption. Adsorption energies are calculated
for six small aromatic molecules (benzene, furan, pyridine, thiophene,
thiophenol, and benzenediamine) and the four DNA nucleobases (adenine,
thymine, guanine, and cytosine) on the (111) surfaces of the three
coinage metals (copper, silver, and gold). For benzene, where the
experimental reference data is most precise, the mean absolute error
in the computed absorption energies is 0.04 eV. For the other aromatic
molecules, the computed binding energies are found to be within 0.09
eV of the available reference data, on average, which is well below
the expected experimental uncertainties for temperature-programmed
desorption measurements. Unlike other dispersion-corrected functionals,
adequate performance does not require changes to the canonical XDM
implementation, and the good performance of XDM is explained in terms
of the behavior of the exchange hole. Additionally, the base functional
employed (B86bPBE) is also optimal for molecular studies, making B86bPBE-XDM
an excellent candidate for studying chemistry on material surfaces.
Finally, the noncovalent interaction (NCI) plot technique is shown
to detect adsorption effects in real space on the order of tenths
of an eV.