Jörg Saßmannshausen jorg.sassm... at strath.ac.uk
Thu Apr 2 23:36:01 UTC 2009

Dear Marc,

as far as I understood it from the Tutorial, it works like that:
Imagine 2 loops, the inner and the outer SCF cycle. First you run the inner 
cycle. If it converges, you only have one outer cycle done (starting the 
inner cycle). 
If the inner cycle does not converge, rather then going down 'the wrong path', 
you go back (into the outer cycle), make some corrections, and go into the 
inner cycle again (so second outer circle run). By doing so, the chances of 
convergence are increased.
I am sure somebody an give a less pictorial and more mathematical 
interpretation of that, but that was my understanding at the time.

I am aware that this methode is used by other programs as well but in a 
different manner.

Right, I am tired, braindead and prolly that is full of typos.

All the best


On Donnerstag 02 April 2009 marc wrote:
> Dear all,
> I'm trying to get a better understanding of the different options that
> are available in cp2k by reading some papers and also to get a more
> hands-on experience with DFT-calculations I'm comparing the results of
> different functionals.  To get some help I was reading the cp2k user
> self-support(part 3) and there I came across the OUTER_SCF option
> (FORCE_EVAL%DFT%SCF%OUTER_SCF).  So my question
> is what does an outer_scf cycle do exactly?  I didn't find any
> reference to the literature or something similar...  Apparently it is
> important for the convergence but I don't really see how.  And what is
> the relation to the 'inner scf' cycle?  There should be an important
> interaction between the two because the total number of iteration
> steps is the product of the maximum internal and maximum external
> steps...
> Maybe this explained somewhere in a paper?
> Thanks in advance,
> marc

Jörg Saßmannshausen
Research Fellow
University of Strathclyde
Department of Pure and Applied Chemistry
295 Cathedral St.
G1 1XL

email: jorg.sassm... at strath.ac.uk
web: http://sassy.formativ.net

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