[Pw_forum] Ionic relaxation with BFGS

[Paolo Giannozzi]

On Mon, 2013-06-03 at 13:53 -0400, feng.zimin at ireq.ca wrote:

> When the relaxation ends, it doesn't seem to me that the force is below
> the value of **forc_conv_thr**.

it isn't, because you set ridicolously low thresholds for convergence.
In fact:

     The maximum number of steps has been reached.

     End of BFGS Geometry Optimization

> Actually AFTER the final step, it does yet another calculation
> of the forces (with the same atomic positions as the previous step)

and it explains why and what may happen:

     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.

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