Improving the First-Principles Description of van der Waals Interactions in Bulk Metals

Due to the coexistence of nearly free and bound electrons, the first-principles computation of van der Waals (vdW) interactions in metals is extremely challenging. These electrons have different response properties and could not be treated on equal footing. Based on a variant of the many-body dispersion method, here we introduce a novel vdW-inclusive approach, named MBD-ϵ, that (i) effectively separates bound and metallic electrons, (ii) screens the Coulomb interaction based on the metallic charge, and (iii) computes the many-body vdW correlation energy between bound states. The remaining long-range correlations due to the nearly homogeneous electron gas are fairly captured by semilocal exchange-correlation functionals. Tests performed on rare-earth elements, transition metals, and main group metals evidence consistent accuracy improvement with respect to broadly adopted vdW approaches. In particular, metallic screening cures systematic overbinding issues, significantly improving equilibrium lattice constants.