[Pw_forum] vdW force in mm_dispersion.f90 and Van der Waals functional

[yukihiro_okuno at fujifilm.co.jp]

Dear PWSCF developers.

I want to evaluate the force from vdW interaction and

compare the DFT-D and vdW functional implemented in PWSCF.

Then, I saw the source code of mm_dispersion.f90, the implementation of
DFT-D.

I found in force_london in mm_dispersion Modules,  a condition

IF (ata /= atb) THEN

....


ENDIF

But,  if ata ==atb ( same atom in the system), there must be  a
contribution of vdW force

from  the periodic images of the same atom (index =ata=atb)  within the
cutoff radius of vdW,

I think the condition (if ata/=atb)  drops such a contribution.


And  in CVS version of PWSCF implementation of  vdW functional in vDW_DF
Modules,

it seems there is a stress calculation function, but still  no force
calculation function

within non-local vdW functional.  Are there plan to implement the force
from vdW

interaction within SCF scheme.


Sincerely.

Yukihiro Okuno.