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

Is the plasmon description within the nonlocal correlation of the van der Waals density functional by Dion and coworkers (vdW-DF) robust enough to describe all exchange-correlation components? To address this question, we design an exchange functional based on this plasmon description as well as recent analysis on exchange in the large-$s$ regime. In the regime with reduced gradients $s=|\ensuremath{\nabla}n|/2n{k}_{\mathrm{F}}(n)$ smaller than $\ensuremath{\approx}2.5$, dominating the nonlocal correlation part of the binding energy, the enhancement factor ${F}_{x}(s)$ closely resembles the Langreth-Vosko screened exchange. In the $s$ regime beyond, dominated by exchange, ${F}_{x}(s)$ passes smoothly over to…

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