[QE-users] phonon dispersion relation from the full IFCs

[Lorenzo Paulatto]

> Thank you for reply, professor. I understand the regular routine 
> implemented in QE where the long-range contribution is added in 
> reciprocal space. My point is can I get the correct dynamical matrix 
> just by making inverse Fourier transformation of the full(short+long) 
> IFCs in a large real space?
> 

The dynamical matrix at Gamma is discontinuity with respect to the 
points nearby, which would make any Fourier transform impossible to 
converge.

I think you should explain WHY you want to do this, and you may get some 
better answer.

In practice, if I was obliged at gunpoint, I would replace the dynamical 
matrix file at Gamma (typically dyn1) with one computed very close to 
Gamma, let's say q=0.001,0,0. Edit the file to trick q2r into thinking 
that it was done at exactly Gamma, and see was comes out.

If the material has a non-analytic term (i.e. the long range term 
depends on the direction), this will definitely not work. Otherwise, you 
may get something decent.


cheers



-- 
Lorenzo Paulatto - Paris