[Pw_forum] nstep parameter for geometry optimization

Jan Gryko gryko at jsu.edu
Tue Dec 10 04:13:58 CET 2013


 I am trying to optimize geometry of a FCC crystal containing 36 atoms. 
 The optimization runs fine, but pw.x stops after 3 bfgs steps with a 
  The maximum number of steps has been reached

  End of BFGS Geometry Optimization

  I increased the n step parameter to nstep=1000, but no change.

 The total force is very small, Total force = 0.000178 (Ry/au),
 and the largest force acting on atom is approx. 0.000029 (Ry/au).

 Does this mean that forces are too small and optimization must stop 
 at this point?

 Unfortunately, even with such small forces, a number of 
 vibrational frequencies calculated by the PHONON run is still negative.

 Any suggestions?

 Thank you very much,

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