Hi,

I am very confused by the Abinit literature.

It says for vdw-xc: 7: apply vdw-DFT-D3(BJ) as proposed by Grimme (based on Becke-Jonhson method J. Chem. Phys. 2004-2006)

Available only for ground-state calculations and response functions; see vdw_tol variable to control convergency

I go to vdw_tol.

there it says:

Only relevant if vdw_xc==5

Ok. Great.

So I do a bunch of relaxations and I notice while using vdw == 7 the following: --------------------------------------------------------------

Van der Waals DFT-D3 semi-empirical dispersion potential

with Becke-Jonhson (BJ) refined by Grimme et al. J.

Comput. Chem. 32, 1456 (2011)

---------------------------------------------------------------

Scaling factors: s6 = 1.000, s8 = 0.787

Damping parameters: a1 = 0.429, a2 = 4.441

Cut-off radius = 1.20806E+02 Bohr

Number of pairs contributing = 2051514

DFT-D3 (no 3-body) energy contribution = -4.52233E-01 Ha

----------------------------------------------------------------

AND NOW I AM REALLY WORRIED:

THe last line says (no 3-body)!

I go back to the literature, and see another variable: vdw_tol_3bt

But it says:

Only relevant if vdw_xc == 6

AND more importantly:

Default is -1 (Comment: Do include the 3-body term in the correction). --- [Note:This comment is not mine -- it is in the literature]

BUT, then in contradiction:

Control the computation of the 3-body correction inside DFT-D3 dispersion correction (Grimme approach) to the total energy:

-If vdw_tol_3bt<0, no 3-body correction.

-If vdw_tol_3bt>0, the 3-body term is included with a tolerance = vdw_tol_3bt

So, now totally confused but disturbed that my output has been yielding "(no-3 body)"

I decide to set it and compare to my earlier runs --I set it to

vdw_tol_3bt == 1d-10 (just like the default value for vdw_tol).

And now I get an output with 3 body energy corrections -- I think:

--------------------------------------------------------------

Van der Waals DFT-D3 semi-empirical dispersion potential

with Becke-Jonhson (BJ) refined by Grimme et al. J.

Comput. Chem. 32, 1456 (2011)

---------------------------------------------------------------

Scaling factors: s6 = 1.000, s8 = 0.787

Damping parameters: a1 = 0.429, a2 = 4.441

Cut-off radius = 1.20806E+02 Bohr

Number of pairs contributing = 2051500

DFT-D3 (no 3-body) energy contribution = -4.52234E-01 Ha

---------------------------------------------------------------

3-Body Term Contribution:

Number of shells considered = 12

Additional 3-body contribution = 2.68812201945E-02 Ha

Total E (2-body and 3-body) = -4.25353118753E-01Ha

---------------------------------------------------------------

My question to ABINIT:

Which is the correct way to use vdw == 7????

thanks,

JB