[Wien] Basic question regarding mixing parameter & force optimization

[Laurence Marks]

On Wed, Oct 6, 2021, 2:20 AM Tran, Fabien <fabien.tran at tuwien.ac.at> wrote:

> 0.01 should in principle leads to slower convergence, except of course if
> 0.2 is too large and does not allow for convergence at all.
>

Sorry, but this is not how the mixing code works. The input parameter
mainly controls the maximum unpredicted step, and small values trigger a
few internal parameters to be more conservative. If you do "grep :MIX
*.scf" you can see how the GREED is dynamically changing.

The commonly seen statement in dft folklore "reduce the mixing factor if it
does not converge" is a misunderstanding of the math.

>
> If the convergence can be achieved properly with 0.2 and 0.01, then the
> results should be identical.
>
> ________________________________________
> From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of shamik
> chakrabarti <shamik15041981 at gmail.com>
> Sent: Wednesday, October 6, 2021 8:29 AM
> To: A Mailing list for WIEN2k users
> Subject: [Wien] Basic question regarding mixing parameter & force
> optimization
>
> Dear Wien2k users,
>
>                          I have few questions regarding mixing parameters
> & force optimization
> (1) If we reduce the mixing parameter from 0.2 to say 0.01, whether the
> convergence will come slowly?
> (2) Whether it will be accurate?
> (3) If we do not get force convergence with PORT should we go for
> NEWT/NEW1?
>
> Any response will be eagerly awaited.
>
> with regards,
>
> --
> Dr. Shamik Chakrabarti
> Research Fellow
> Department of Physics
> Indian Institute of Technology Patna
> Bihta-801103
> Patna
> Bihar, India
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