Using MetaGGA fundtional with optB88-vdW Nonlocal correction

[burakgurlek]

Hi,

I would like to use R2SCAN functional with optB88-vdW nonlocal correction. I saw that IVDW_NL=1 suppose to make it, but I get an error " The GGA and METAGGA tags can not be used at the at the same time". Is there any way around?

INCAR file is
SYSTEM = TNS DFT

#calculation
PREC = FAST
EDIFF = 1e-6
EDIFFG = 0.00001
KPAR = 8
NCORE = 10
METAGGA=R2SCAN

#electronic states
ISMEAR = 0 !this is fermi-dirac smearing
SIGMA = 0.01 !value for smearing in eV
NBANDS = 80
NELM = 250 !maximum number of scf steps
NELMIN = 3

#Relaxation
NSW = 400
IBRION = 2
POTIM = 0.05
ISIF = 2
ISYM = -1

LASPH =.TRUE.
IVDW_NL=1

#vdw-Langreth
GGA = BO #optB88-vdw
PARAM1 = 0.1833333333 #default
PARAM2 = 0.2200000000 #default
LUSE_VDW = .TRUE.
AGGAC = 0.0000 #default

Regards,
Burak

[fabien_tran1]

Hello,

The optB88-vdW functional consists of three components:
(a) GGA-optB88 exchange (specified with GGA=BO and PARAM1 and PARAM2).
(b) LDA correlation (set with AGGAC=0.0000 which switches off the GGA correction in the PBE correlation).
(c) The nonlocal vdW term.

A functional consisting of the vdW term combined with r2SCAN instead of GGA-optB88+LDA-corr. (is it what you want to do?) has to be specified like this:
METAGGA=R2SCAN
LUSE_VDW = .TRUE.
IVDW_NL=1
while the tags GGA, PARAM1, PARAM2 and AGGAC have to be removed from the INCAR. Note that the tag IVDW_NL is available since VASP.6.4. Besides, I don't think that r2SCAN+vdW is a good functional for the accuracy.

[burakgurlek]

Hi,

thanks for the suggestion, but I do not get which VDW is used with
METAGGA=R2SCAN
LUSE_VDW = .TRUE.
IVDW_NL=1

It is not GGA-optB88+LDA-corr. What does IVDW_NL=1 do?
I indeed want to use R2SCAN with D2 correction, but the parameters are not know, neither for D3.

Regards,
Burak

[fabien_tran1]

There are several vdW methods implemented in VASP. They are listed at Van der Waals functionals, and how to use them is explained at IVDW and LUSE_VDW.

If you read these pages, you can see that what was specified in your INCAR (LUSE_VDW and IVDW_NL) concerns the nonlocal vdW-DF functional. For D2 or D3, you need to use IVDW=1, 12 or 13. Indeed, the D2/D3 parameters for r2SCAN are not available. If values are available in the literature, then you can manually specify them in the INCAR, as explained at DFT-D2 and DFT-D3.

[fabien_tran1]

If there is no D2/D3 parameters for r2SCAN available in the literature, then it would make sense to use the values for SCAN (similar to r2SCAN) that exist for D3. You can find the SCAN values in the fortran file subdftd3.F.