[Q-e-developers] Dielectric constant using PHONON, with and without GAMMA tricks

[Paolo Giannozzi]

On Mon, 2012-12-03 at 15:25 -0800, Marco Govoni wrote:

> If I use phcg.x (on top a SCF calculation with KPOINT(gamma) ), I get epsilon_XX = 4.565220 .
> If I use ph.x (on top a SCF calculation with KPOINT(automatic) 111 000 ), I get epsilon_XX = 4.966717159 .
> Why the two numbers are different? 

because the criteria for convergence that you have set is
1) a few orders of magnitudes too large for good results, and
2) not the same for the two codes (one is on the value of Delta V,
another is on the norm of the residual vector)
If you decrease it, in particular the one for ph.x, you get more or 
less the same numbers in the two cases
 
P.
-- 
Paolo Giannozzi, IOM-Democritos and University of Udine, Italy