[Wien] Basic question regarding mixing parameter & force optimization

[Tran, Fabien]

I think that the original question of Shamik concerns PORT, and not MSR1. In some cases, in particular with non-standard potentials, I could converge only with PORT and with a very small mixing (typically 0.02). Then, I was checking what happens if the calculation is restarted (after a save_lapw) with normal mixing scheme (MSR1 with 0.20), and in most cases (but not all) it was ok (no pseudo-convergence).

________________________________________
From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of Laurence Marks <laurence.marks at gmail.com>
Sent: Wednesday, October 6, 2021 9:48 AM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] Basic question regarding mixing parameter & force optimization

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

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From: Wien <wien-bounces at zeus.theochem.tuwien.ac.at<mailto:wien-bounces at zeus.theochem.tuwien.ac.at>> on behalf of shamik chakrabarti <shamik15041981 at gmail.com<mailto: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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