[Pw_forum] WFC convergence in NEB calculation

[Paolo Giannozzi]

On Oct 10, 2008, at 19:15 , Janos Kiss wrote:

> Is this behavior completely normal in an NEB calculation with  
> PWSCF, or this
> is an issue with my particular system/setup only?

the latter you say, and a bit of the former as well: your particular  
system seems
to be a nasty one, and NEB typically explores strange geometrical  
configurations
that are sometimes hard to converge.

> What else could one try, to get the wfc somehow converged?

hard to say (especially withouth the ouput). Are you sure that spin  
polarization
is not a source of trouble close to the transition state?

One possible trick could be to go on with the calculation even if not  
converged.
I am actually considering adding yet another option  
("sloppy_convergence"?)
doing exactly this. It should be easy: in PW/electrons.f90, set  
"conv_elec" to
.true. at the last iteration, after the call to "mix_rho". No warranty.

> Another question: when i restart an NEB calculation, how can i  
> restart the wfc
> for those images, which were already converged for a given NEB  
> iteration?
> [...] even for those images, where the wfc was converged, i still  
> need to
> spend again like 5-9 SCF cycles/image.

are you sure that the code is using the same set of coordinates that  
were used
in the previous calculation? Maybe the restart doesn't work as expected.

> What am i doing wrong?

maybe nothing. NEB is relatively new and its application may  
encounter some
difficulties, until more experience is gathered (and better  
algorithms implemented).

Paolo
---
Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222