[Wien] Basic question regarding mixing parameter & force optimization

[shamik chakrabarti]

Dear Prof. Marks,

                           Thank you for your explanations Sir. Comments
are very informative.

with regards,

On Wed, 6 Oct 2021 at 18:30, Laurence Marks <laurence.marks at gmail.com>
wrote:

> Some mixer and optimization comments, to clarify.
>
> 99.999% of cases where there are convergence problems are due to:
>
> 1) Inappropriate physics. A bad model does not have to have a fixed-point
> solution, that is there may be no converged solution. (Nothing says there
> has to be.)
>
> 2) Inappropriate numerics. For instance, a functional that jumps around
> very noisily may not be smooth. I know this can happen for 4f electrons
> using -eece.
>
> 3) Discontinuity at the solution. There is such a discontinuity
> (electronic phase transition) for systems such as isolated Fe atoms without
> spin, T=0.
>
> 4) User error. I recently ran a case with 16 symmetry elements which only
> should have had 8. While it came close, it would not converge.
>
> Sometimes the pseudo-forces are quite bad with large density residues, so
> MSR1a can be slow. There can also be issues if the electron-phonon coupling
> is large.
>
> PORT is sometimes better, particularly with repetitive calculations such
> as lattice parameter optimizations. However, it is very sensitive to
> inconsistent forces and energies.
>
> In my opinion NEWT & NEWT1 should be removed. My opinion.
>
> Always look first at how the model is setup.
>
> --
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought" Albert Szent-Györgyi
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> SEARCH the MAILING-LIST at:
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
>


-- 
Dr. Shamik Chakrabarti
Research Fellow
Department of Physics
Indian Institute of Technology Patna
Bihta-801103
Patna
Bihar, India
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://zeus.theochem.tuwien.ac.at/pipermail/wien/attachments/20211006/0a979d96/attachment.htm>