[CP2K-user] Convergence with CUTOFF

Travis polla... at gmail.com
Mon Jan 27 08:54:33 UTC 2020


Vacuum is expensive with plane wave methods. Your box only needs to be 
large enough that the density goes to zero at the boundaries (6-10 
Angstroms) with the wavelet solver. You'll see a warning about non-zero 
density if you don't use a large enough box. The rule of thumb for the 
cutoff is to multiply the largest exponent in the basis by REL_CUTOFF. For 
your basis set and REL_CUTOFF, that's about 1500 Ry. This puts the tightest 
orbital on the finest grid.


On Monday, January 27, 2020 at 3:02:14 AM UTC-5, coko312 wrote:
> Dear all,
> I am a cp2k-DFT beginner so the answer to this question may seem obvious 
> to you, but it would help me a lot!
> I try to converge the total energy of a single Na+ ion as a function of 
> the energy CUTOFF, but the convergence is very slow and even using 900 Ry 
> is not fully satisfactory for what I want to do. Even with no experience 
> with this system, I would not expect the computation to last several hours 
> on a single processor for only 1 atom. I have attached my input-output 
> files. What should I modify to be able to use a more reasonable CUTOFF? 
> NB : the computation is non-periodic because I would like, next, to add 
> more atoms around to compute interaction energies between these little 
> "clusters" and various types of molecules.
> Best,
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