[Pw_forum] problem with relaxation and difference between SCF Fermi level and DOS Fermi level

[Paolo Giannozzi]

On Thu, 2014-03-13 at 09:07 +0200, Uri Argaman wrote:


> 1. When I do vc-relax calculation to determine the pressure I get the
> desired pressure but in the last iteration I get a large jump in the
> pressure (after "begin final coordinate") sometimes in the order of
> 1000 kbar. Why is it happening and how can I fix it?

this is what the code prints just after "end final coordinates":

     A final scf calculation at the relaxed structure.
     The G-vectors are recalculated for the final unit cell
     Results may differ from those at the preceding step.
 
Remember that variable-cell calculations are performed with G-vectors
from the starting cell. If the jump is large, your cutoff is far from
convergence (and the final cell is quite different from the initial one)

> 2. I notice that the Fermi level in the SCF file is not the same as
> the Fermi level in the DOS file. Why is that?

the non-scf calculation ('nscf') for dos re-computes the Fermi energy.
If there is a significant difference between the k-point grid used in
the scf and in the nscf cases, you may get some minor differences in
the Fermi energy as well.

P.
> Thank you very much
> 
> 
> Uri Argaman
> 
> Ben-Gurion University
> 
> Israel
> 
> 
> 
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-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222