[Wien] Energy is converge but charge is not good converge，why？

[Stefaan Cottenier]

> I have calculated the Ni slab, when the energy was converge, I found
> that the charge is not good converge. I do not know why this case is
> happened and if or not this case  is correct. Please give me much
> suggestion or other understanding. Thanks in advance.

Energy tends to converge faster than charge distance, hence what you 
observe is normal.

If your property of interest is one that converges slowly too (forces, 
for instance), that property might not yet be converged when you stop 
the calculation at energy convergence.

Looking at energy convergence only has the danger as well that you might 
stop at a 'plateau', i.e. the calculation looks converged for a while, 
but would still qualitatively change if you converge further.

As a general rule, it is safest to go for a fair charge distance 
convergence (search older posts by Laurence Marks to have specific 
values for -cc in combination with -ec and -fc).

Stefaan