Reference : Electronic Exchange and Correlation in van der Waals Systems: Balancing Semilocal and...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Chemistry
Physics and Materials Science; Computational Sciences
Electronic Exchange and Correlation in van der Waals Systems: Balancing Semilocal and Nonlocal Energy Contributions
Hermann, Jan []
Tkatchenko, Alexandre mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) > Physics and Materials Science Research Unit >]
Journal of Chemical Theory and Computation
[en] Short-range correlations in motion of electrons in
matter are captured well by semilocal exchange−correlation (XC)
functionals in density functional theory (DFT), but long-range
correlations are neglected in such models and must be treated by
van der Waals (vdW) dispersion methods. Whereas the effective
range of distances at which fluctuations are correlated is usually
explicit in the vdW models, the complementary range of semilocal
functionals can be observed only implicitly, requiring an
introduction of empirical damping functions to couple the
semilocal and nonlocal contributions to the XC energy. We
present a comprehensive study of the interplay between these
short-range and long-range energy contributions in eight semilocal
functionals (LDA, PBE, TPSS, SCAN, PBE0, B3LYP, SCAN0,
M06-L) and three vdW models (MBD, D3, VV10) on
noncovalently bonded organic dimers (S66×8), molecular crystals (X23), and supramolecular complexes (S12L), as well as
on a series of graphene-flake dimers, covering a range of intermolecular distances and binding energies (0.5−130 kcal/mol). The
binding-energy profiles of many of the DFT+vdW combinations differ both quantitatively and qualitatively, and some of the
qualitative differences are independent of the choice of the vdW model, establishing them as intrinsic properties of the respective
semilocal functionals. We find that while the SCAN+vdW method yields a narrow range of binding-energy errors, the effective
range of SCAN depends on system size, and we link this behavior to the specific dependence of SCAN on the electron
localization function α around α = 1. Our study provides a systematic procedure to evaluate the consistency of semilocal XC
functionals when paired with nonlocal vdW models and leads us to conclude that nonempirical generalized-gradient and hybrid
functionals are currently among the most balanced semilocal choices for vdW systems.

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