[Pw_forum] Hellmann Feynmann forces in QE

[Stefano Baroni]

Forces are 1st order derivatives of the energy. Phonon frequencies are 2nd order. Of course, you do not need the latter to compute the former. As others have already said, forces are calculated by pw.x, whereas vibrational frequencies are calculated by ph. x. HTH - SB

--
Stefano Baroni, Trieste -- swift message written and sent on the go

On 16/feb/2012, at 22:59, Elie M <elie.moujaes at hotmail.co.uk> wrote:

> Hello all,
> 
> Just a quick question. Is there a way , when doing phonon calculations in QE, to just extract the Hellmann Feynamnn forces exerted on the atoms without going the whole way and compute the phonon frequencies?
> 
> Thanks
> 
> Elie M
> University of Nottingham
> NG7 2RD
> UK
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