[Pw_forum] Real space force constants file

[Sridhar Sadasivam]

Thanks so much Prof. Giannozzi. I apologize for repeating the question.
Sridhar


On Wed, May 28, 2014 at 1:31 AM, Paolo Giannozzi
<paolo.giannozzi at uniud.it>wrote:

> I just added point 7.7 of the FAQs, since this question is asked
> more often than not: http://www.quantum-espresso.org/faq/phonons/#7.7
>
> P.
>
> On Tue, 2014-05-27 at 09:20 +0530, Sridhar Sadasivam wrote:
> > Dear QE users and developers,
> >
> >
> > I am trying to use the real space force constants file obtained from
> > q2r.x to do some other calculations outside of QE. For this purpose, I
> > am trying to understand the format of the force constants file. I am
> > attaching a sample force constants file obtained by performing ph.x
> > and q2r.x on bulk silicon with a 4 x 4 x 4 q-mesh.
> >
> >
> > In the 22nd line in the file, it says 1 1 1 1. I believe the first two
> > 1's denote the x-direction and the last two 1's denote atom numbers
> > within the two-atom unit cell of silicon. After this it loops over all
> > 64 different combinations of indices in a 4 x 4 x 4 mesh and lists the
> > force constants in the 4th column. What do these 64 different
> > combinations mean? Do they denote unit cells?
> >
> >
> > For instance, let's take the first line: 1 1 1 2.6997. 2.6997 is the
> > force constant between which atoms?
> >
> >
> > Thanks for your help!
> > Sridhar
> > Purdue University
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>
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