An exchange functional that tests the robustness of the plasmon description of the van der Waals density functional

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Is the plasmon description within the non-local correlation of the van der Waals density functional by Dion and coworkers (vdW-DF1) robust enough to describe all exchange-correlation components? To address this question, we design an exchange functional, termed LV-PW86r based on this plasmon description as well as recent analysis on exchange in the large s-regime. In the regime with reduced gradients s=|∇ n|/2n k F(n) smaller than ≈ 2.5, dominating the non-local correlation part of the binding energy, the enhancement factor Fₓ(s) closely resembles the Langreth-Vosko screened exchange. In the s-regime beyond, dominated by exchange, Fₓ(s) passes smoothly over to the revised Perdew-Wang-86 form. Our tests indicate that vdW-DF1(LV-PW86r) produces accurate separations and binding energies of the S22 data set of molecular dimers as well as accurate lattice constants of layered materials and tightly-bound solids. These results suggest that vdW-DF1 has a good plasmon description in the low-to-moderate s-regime.