[Wien] Charge convergence necessity

[Pascal Boulet]

Dear all,

This question recalls me something I read about DFT a (very) long time ago… Isn’t there also a fundamental reason specifically to DFT that we should not only converge the energy but also (and above all?) the density? 

Best regards,
Pascal

Le 16 juil. 2015 à 02:26, Laurence Marks <L-marks at northwestern.edu> a écrit :

> 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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--
Pascal Boulet - MCF HDR, Resp. L1 MPCI - DEPARTEMENT CHIMIE
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