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

• Published in: Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2014-01, Vol.89 (3), Article 035412
• Main Authors: Berland, Kristian, Hyldgaard, Per
• Format: Article
• Language: English
• Subjects: Binding energy; Condensed matter; Correlation; Density; Design engineering; Exchange; Lattice parameters; Plasmons; Robustness
• ISSN: 1098-0121; 1550-235X
• DOI: 10.1103/PhysRevB.89.035412

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 = [Hamiltonoperator]n2nk sub(F) (n) smaller than 2.5, dominating the nonlocal correlation part of the binding energy, the enhancement factor F sub(x)(s) closely resembles the Langreth-Vosko screened exchange. In the s regime beyond, dominated by exchange, F sub(x)(s) passes smoothly over to the revised Perdew-Wang-86 form. We term the specific exchange functional LV-PW86r, wheras the full van der Waals functional version emphasizing consistent handling of exchange is termed vdW-DF-cx. Our tests indicate that vdW-DF-cx produces accurate separations and binding energies of the S22 data set of molecular dimers as well as accurate lattice constants and bulk moduli of layered materials and tightly bound solids. These results suggest that the plasmon description within vdW-DF gives a good description of both exchange and correlation effects in the low-to-moderate s regime.