# CUTOFF convergence problem

katarína stančiaková stanc... at gmail.com
Wed Nov 11 15:58:56 UTC 2015

```Dear Matt,
thank you very much your reply. I will try to use different basis sets to
see if the results will change.

You are right, I am comparing the energy differences after geometry
optimizations and it seems that with different cutoff values I am finding
different minima. What is bothering me is that even CUTOFF 1200 Ry is
obviously not enough as I found another minima for structure 1 with cutoff
1400 Ry. The using of such high cutoff is not very convinient for zeolite
structures as far as I know. So I am looking for some "bug" in my setup.

Katarina

Dňa utorok, 10. novembra 2015 10:13:10 UTC+1 Matt W napísal(-a):
>
> Hi Katrina,
>
> At a given geometry (the one in your input) the total energy of the system
> converges quite OK with cutoff after about 800 Ry, according to me.
>
> Are you comparing the energy differences after performing geometry
> optimization? Is it possible that a some of your runs are optimizing to
> subtly different structures. Even a tiny difference in the shape of the
> potential energy surface can lead you into a different minima, are you are
> starting from quite high energy structures it seems. Your structure 2 seems
> well behaved, but structure 1 gives a weird energy at the highest cutoff
> you used.
>
> Matt
>
> BTW, the basis sets you are using DZV-GTH are probably not really
> production quality.
>
> On Monday, November 9, 2015 at 3:33:32 PM UTC, katarína stančiaková wrote:
>>
>> Dear CP2K users,
>> I am running my calculations and I have CUTOFF convergence problem - in
>> fact I can not see any convergence in the total energy. I know that the
>> relative differences in energies are important (not the absolute values of
>> energies), therefore I am comparing the energy differences between two
>> structures (I am working with zeolites, and my two structures differs in
>> the position of hydrogen). Even with very high cutoff values I can not
>> observe any convergence of the total energies as well as energy differences.
>> Do you have any idea where is the problem? I will be thankful for any
>> help!
>>
>> Here are my data:
>>
>> CUTOFF [Ry]            Total Energy [a.u.]
>>                                 structure 1                structure 2
>> 600                           -3467.0403965424    -3467.0619253888
>> 800                           -3467.0521866655    -3467.0622253178
>> 1000                         -3467.0838714739    -3467.1096147317
>> 1200                         -3467.0833499728    -3467.1103018678
>> 1400                         -3467.0975445683    -3467.1102723936
>>
>>
>> ENERGY DIFFERENCES
>>
>>
>> CUTOFF [Ry]    E_str1 - E_str2 [kJ/mol]
>>
>> 600                55.9750007029
>> 800                26.1004960059
>> 1000              66.932470253
>> 1200              70.0749269477
>> 1400              33.0923456248
>>
>> Thank you
>> Katarina
>>
>
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