[Pw_forum] Does total force include dispersion force?

Gabriele Sclauzero gabriele.sclauzero at epfl.ch
Thu Nov 24 13:47:42 CET 2011

Dear Wu,

Il giorno 24/nov/2011, alle ore 12.44, WF ha scritto:

> Hello everyone,
>          I am doing a vc-relax calculation with PBE+D ( with .london. = true and PBE functional). In the output, an additional part called “Dispersion forces acting on atoms” is displayed after “Total forces acting on atoms” after each BFGS cycle. Do the values in total force part already include dispersion forces ? I am not sure with what I read from the codes.

What have you read from the codes?

If you read inside PW/forces.f90 you will find:

        IF ( llondon ) force(ipol,na) = force(ipol,na) + force_disp(ipol,na)

The "dispersion force" is added to the total force (before printing), therefore what you find in the output does actually include also the dispersion contribution that is printed separately. 

Indeed I think it may be a bit misleading to print by default that contribution, while for all other cases (e.g. Hubbard U and similar) this is done only with verbosity="high".

> Thanks very much.

You're welcome,


> ------------------------------------
> Wu F,
> College of Chemistry and Molecular Engineering, Peking University.
> ------------------------------------
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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