[Wien] Charge convergence necessity

[Laurence Marks]

I don't think I can give a complete answer, but I will make one point. It
can easily happen that the energy convergence appears to be OK, but the
charge convergence is not. The reason is that the energy convergence is
measured as a change in energy over the last few iterations, whereas the
charge convergence is based upon the difference of the initial and final
densities in the current cycle. If, for whatever reason, the mixer is only
taking very small steps the energy can appear to have converged, but in
reality the true self-consistent solution (fixed point) has not been
reached.

Hence I almost always add something like -cc 0.001 as a minimum level. If I
really want to be certain about the fixed point I might decrease this by a
factor of 4-10, never more than this.

N.B., for a preconvergence before switching to MSR1a -cc 0.05 is often good
enough.


On Wed, Jul 15, 2015 at 7:08 PM, Luis Ogando <lcodacal at gmail.com> wrote:

>   Dear Wien2k community,
>
>     I would like to know in which situations the charge convergence is
> really necessary.
>     All the best,
>                   Luis
>
>


-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: MURI4D.numis.northwestern.edu
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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