[DFTB-Plus-User] regarding forces module

Bálint Aradi aradi at uni-bremen.de
Fri Aug 25 13:35:34 CEST 2017

Dear Sharma,

> I read the comments above the loop. But, it is not clear to me from
> these comments that why the first loop in the derivative_nonSCC routine,
> i.e.,
>           do ii = 1, 3
>             deriv(ii,iAtom1) = deriv(ii,iAtom1) &
>                 &+ sum(sqrDMTmp(1:nOrb2,1:nOrb1)&
>                 &* 2.0_dp*hPrimeTmp(1:nOrb2,1:nOrb1,ii)) &
>                 &- sum(sqrEDMTmp(1:nOrb2,1:nOrb1)&
>                 &* 2.0_dp*sPrimeTmp(1:nOrb2,1:nOrb1,ii))
>           end do
> is not sufficient to describe the force on iAtom1? 

The loop is not sufficient, as our neighbor list over which the outer
loop (do iNeigh = 1, ...) runs only contains half of the neighborship
relations. (For each atom, only neighbors are recorded, which have an
index higher than the atom itself.) Therefore, you have to make sure,
you sum up the contribution for the missing neighbors.

> P. S.: May I also know, why derivative_nonSCC is separately made public
> despite its availability through the derivative_shift interface?

That seems to be inconsistent coding style at the first glance, indeed.
We'll fix that.



Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen

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