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 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum