Extent of Fock-exchange mixing for a hybrid van der Waals density functional?
Journal article, 2018

The vdW-DF-cx0 exchange-correlation hybrid design [K. Berland et al., J. Chem. Phys. 146, 234106 (2017)] has a truly nonlocal correlation component and aims to facilitate concurrent descriptions of both covalent and non-covalent molecular interactions. The vdW-DF-cx0 design mixes a fixed ratio, a, of the Fock exchange into the consistent-exchange van der Waals density functional, vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)]. The mixing value a is sometimes taken as a semi-empirical parameter in hybrid formulations. Here, instead, we assert a plausible optimum average a value for the vdW-DF-cx0 design from a formal analysis; A new, independent determination of the mixing a is necessary since the Becke fit [A. D. Becke, J. Chem. Phys. 98, 5648 (1993)], yielding a 0 = 0.2, is restricted to semilocal correlation and does not reflect non-covalent interactions. To proceed, we adapt the so-called two-legged hybrid construction [K. Burke et al., Chem. Phys. Lett. 265, 115 (1997)] to a starting point in the vdW-DF-cx functional. For our approach, termed vdW-DF-tlh, we estimate the properties of the adiabatic-connection specification of the exact exchange-correlation functional, by combining calculations of the Fock exchange and of the coupling-constant variation in vdW-DF-cx. We find that such vdW-DF-tlh hybrid constructions yield accurate characterizations of molecular interactions (even if they lack self-consistency). The accuracy motivates trust in the vdW-DF-tlh determination of system-specific values of the Fock-exchange mixing. We find that an average value a 0 = 0.2 best characterizes the vdW-DF-tlh description of covalent and non-covalent interactions, although there exists some scatter. This finding suggests that the original Becke value, a 0 = 0.2, also represents an optimal average Fock-exchange mixing for the new, truly nonlocal-correlation hybrids. To enable self-consistent calculations, we furthermore define and test a zero-parameter hybrid functional vdW-DF-cx0p (having fixed mixing a 0 = 0.2) and document that this truly nonlocal correlation hybrid works for general molecular interactions (at reference and at relaxed geometries). It is encouraging that the vdW-DF-cx0p functional remains useful also for descriptions of some extended systems. Published by AIP Publishing.


Yang Jiao

Chalmers, Microtechnology and Nanoscience (MC2), Electronics Material and Systems Laboratory

Elsebeth Schröder

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

Per Hyldgaard

Chalmers, Microtechnology and Nanoscience (MC2), Electronics Material and Systems Laboratory

Journal of Chemical Physics

0021-9606 (ISSN) 1089-7690 (eISSN)

Vol. 148 19 194115

Pollutant physisorption and weak chemisorption - atomic-scale theory and calculations

Swedish Research Council (VR), 2015-01-01 -- 2018-12-31.

Consistent-exchange van der Waals density functional studies of bonding, morphology changes, and optical response in molecular energy systems

Swedish Research Council (VR), 2015-01-01 -- 2018-12-31.

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)

Materials Science

Subject Categories

Physical Chemistry

Atom and Molecular Physics and Optics

Other Physics Topics

Theoretical Chemistry


Basic sciences


C3SE (Chalmers Centre for Computational Science and Engineering)



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8/3/2020 1