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vdW-DF functional of Langreth and Lundqvist et al.

The vdW-DF proposed by Dion et al. [143] is a non-local correlation functional that approximately accounts for dispersion interactions. In VASP the method is implemented using the algorithm of Roman-Perez and Soler [144] which transforms the double real space integral to reciprocal space and reduces the computational effort. Several propsed versions of the method can be used: the original vdW-DF [143], the ``opt" functionals (optPBE-vdW, optB88-vdW, and optB86b-vdW) where the exchange functionals were optimised for the correlation part [145], and the vdW-DF2 of Langreth and Lundqvist groups [146].

This method is available since the 5.2.12.26May2011 version of VASP for the calculation of total energies and forces. The stress calculation for the cell optimisation (ISIF=3) is available since the VASP 5.2.12.11Nov2011 version for spin unpolarised systems and VASP 5.3.1 for spin polarised systems.

N.B.: This feature has been implemented by J. Klimeš. If you make use of the vdW-DF functionals presented in this section, we ask you to cite Ref. [147]. Please also cite the original vdW-DF paper of Dion et al. [143] and the paper of Roman-Perez and Soler [144]. In addtion, cite the paper of Lee et al. [146] if you use the vdW-DF2 functional, the paper of Klimeš et al. [145] if you use the optB88-vdW or optPBE-vdW functionals, and any other appropriate references, such as Ref. [148].

 
Correlation functionals

The method is invoked by setting

LUSE_VDW = .TRUE.

Moreover, the PBE correlation correction needs to be removed since only LDA correlation is used in the functionals. This is done by setting

AGGAC = 0.0000

The two tags above need to be used for all of the following functionals.

 
Exchange functionals

The GGA tag is further used to choose the appropriate exchange functional. The original vdW-DF of Dion et al uses revPBE, therefore the vdW-DF can be chosen by setting

GGA = RE
LUSE_VDW = .TRUE.
AGGAC = 0.0000

More accurate exchange functionals for the vdW correlation functional have been proposed in [145] and [147]. To use these functionals set:

GGA = OR
LUSE_VDW = .TRUE.
AGGAC = 0.0000

for optPBE-vdW,

GGA = BO
PARAM1 = 0.1833333333
PARAM2 = 0.2200000000
LUSE_VDW = .TRUE.
AGGAC = 0.0000

for the optB88-vdW functional, or

GGA = MK 
PARAM1 = 0.1234 
PARAM2 = 1.0000
LUSE_VDW = .TRUE.
AGGAC = 0.0000

for the optB86b-vdW functional.

In the vdW-DF2 functional the rPW86 exchange functional is used

GGA = ML

moreover, the vdW functional needs to be changed to the vdW2 correlation which requires only a change of a parameter:

Zab_vdW = -1.8867

Therefore to use vdW-DF2, set:

GGA = ML
LUSE_VDW = .TRUE.
Zab_vdW = -1.8867
AGGAC = 0.0000

An overview of the performance of the different approaches can be found for example in [145,146] for gas phase clusters and in [147] for solids.

 
Important remarks:


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Next: Electric Field Gradients Up: The INCAR File Previous: dDsC dispersion correction   Contents   Index
N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at