[DFTB-Plus-User] Convergence issues?

[Bálint Aradi]

Dear Dave Schall,

> I'm trying to do an energy minimization of slab-like planar structure and I
> cannot get convergence of steepest descents or cg method. In a separate, but
> possibly related issue, I can't get the scc calculation to converge either.
> I started with a 1x1 unit cell "slab" of the material, then a 2x2 unit cell
> slab. These both converge in around 8 iterations. If I scale up to 3x3 cells
> or greater, I do not achieve convergence and the energy oscilates or
> actually goes up. Any suggestions for achieving convergence for energy
> minimization and / or scc? Ideally I'd like to scale up to a 10x5 unit cell
> slab for my calculations.
> 
> Attached are the input files for a 2x2 and 3x3 unit cell energy minimization
> calculations with scc off.

 Actually I could not reproduce your problem. I took the 3x3 unit cell
you sent, turned SCC on (which you should, as the pbc set is for SCC
calculations) and got a converged geometry. (See attached input/output).
I used dftb+_s081217, which I recommend to use.

  Best regards,

    Bálint

-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/en/~b_aradi

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