[CP2K:672] Re: Total energy vs volume

[Teodoro Laino]

On 3 Feb 2008, at 19:04, xiaoliang wrote:

> I wonder how cp2k calculate the number of grid points? Because If I
> change the size of reference cell, the number of grid points is
> changed as well, I think. Then do we need to  make energy vs reference
> cell size plot to get energy convergece, like the test for energy vs
> cutoff ?

In principle yes.. but you would discover that to get "full  
convergence" you should reach extremely high cutoff
(unaffordable for standard calculations).
However, the nice thing is that the absolute energy is just shifted  
and the shape of the potential energy  does not change
sensibly. This makes feasible to use a relatively low cutoff (of  
course too small creates problems as well..).
"Generally speaking" a cutoff of around 300 Ry is most of the time  
enough.. of course the real good number depends on the
nature of your basis set, pseudo, XC.

Ciao,
Teo
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