[Pw_forum] Slab optimization with -24kbar stress!!!

[Paolo Giannozzi]

On Thu, 2014-12-04 at 10:26 -0800, David Foster wrote:

> My main problem is final section of the output:
>           total   stress  (Ry/bohr**3)                   (kbar)     P=  -24.51
>   -0.00007691   0.00000000  -0.00000000        -11.31      0.00     -0.00
>    0.00000000  -0.00032173   0.00000000          0.00    -47.33      0.00
>   -0.00000000   0.00000000  -0.00010117         -0.00      0.00    -14.88

> As you see final stress is -24.51 kbar ??????!!!!!!!!!!!!!!

Maybe the explanation is here ??????!!!!!!!!!!!!!!
   http://www.quantum-espresso.org/faq/self-consistency/#6.10
Before the last step, the code should have printed the following
message:

     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.

If your plane-wave basis set is not very converged, and if your
final unit cell volume is significantly different from the starting 
one, you may easily get a few tens of kBar as final pressure
(corresponding to a very small change in volume anyway)

Paolo

-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222