[Pw_forum] query on e-ph matrix element

[Paolo Giannozzi]

On Sun, 2011-12-11 at 00:31 -0500, Ajit Vallabhaneni wrote:

> I had gone thru the source code "elphon.f90" for this purpose.

wow! you are a brave man

> I could figure out all the variables like k,i,j,q but not nu. 
> I see a variable 'imode0' which i cannot figure out its purpose. 
> Can someone please help me with identifying the nu ? 

the el-ph matrix elements are calculated for each irrep, i.e.
displacement patterns transforming into each other under the
symmetry operations of the small group of each wavevector. 
There are nirr irreps, each having dimension npert(irr).
The code runs over irreps: irr=1,..,nirr, then over irrep
components: ipert=1,..,npert(irr), and imode0+ipert is the 
index of each displacement pattern. Only when the el-phon
coefficient "gamma" is calculated are phonon modes (contained 
in matrix "dyn") actually used. 

P.
-- 
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy