Two queries: 1. Broyden mixing, 2. EDIFF convergence

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bth20 · #1 Post by **bth20** » Tue Jul 12, 2005 9:56 am

Hi,

A noncollinear job I was running killed itself (after looking very good). The only thing I can see in OUTCAR that might be relevant is a warning:

WARNING: grid for Broyden might be too small

Any ideas guys? There are various parameters controlling Broyden mixing. Iâ€™m not sure which I should try adjusting.

Also, looking more at the output it seems that it went through all allowed SC iterations (set to 200) despite reaching the required accuracy (EDIFF set to 1.0e-5) well before that . What reasons coule there be for this?

Thanks

Ben

#2 Post by **admin** » Fri Jul 22, 2005 1:45 pm

1)the grid on which Broyden mixing is done is reduced compared to the
full FFT grid, for all wavevectors which are not included in this grid,
a simple mixing is performed. Then, the residuals are compared. If
(rms(total) - rms(broyd)) / rms(total) > 0.1,
this warning is written.
to avoid this error, you can do 2 things
--) decrease the mixing parameters from the default settings
(AMIX,BMIX, AMIX_MAG, BMIX_MAG), which may be useful for slabs, clusters and
magnetic systems
--) increase the FFT grid (by increasing PREC)

2) concerning the changes of TOTEN and EDIFF: there is always one more
step done in order to check whether the energy really is converged to within
the limit set by EDIFF. Only if the difference is smaller than EDIFF for this
step as well, the electronic scf loop is terminated.

jlbettis · #3 Post by **jlbettis** » Mon Feb 07, 2011 1:14 am

I was wondering, 1) how many "WARNING: grid for Broyden might be too small " error messages warrant evasive maneuvers, ie tweaking the INCAR parameters? I have a system in which I only care about convergence of the electronic GS. I receive this WARNING message once or twice; in a total of 4 calculations differing only in magnetic states. The warning appears 10 -12 iterations before convergence. Should I be alarmed. 2) How should one qualify this WARNING? Are there situations in which the WARNING may be disregarded?
<span class='smallblacktext'>[ Edited Mon Feb 07 2011, 02:16AM ]</span>

jlbettis · #4 Post by **jlbettis** » Fri Feb 11, 2011 2:14 am

If the Admin has anything to add, it would be greatly appreciated.