CUTOFF convergence problem

[Matt W]

Hi,

your CUTOFF is still not converged. For PBE and a system with oxygen atoms 
to be fully converged in an individual energy you need to be at > 600 Ry, 
probably somewhat more.

300 -1752.615532 350 -1752.601872 400 -1752.596534 450 -1752.596534 500 
-1752.595309 550 -1752.594747 600 -1752.594059 700 -1752.594543 800 
-1752.594127 900 -1752.594142 1000 -1752.594152 1250 -1752.594154 
Energies vs cutoff for your zeolite system. For a lot of uses you don't 
need to push that hard, but if you are comparing small relative energies, 
it might be needed. If the cost of the cutoff is too high, you can also try 
using the GAPW method or using pseudo potentials with non linear core 
correction. There are several threads mentioning these on the forum.

Matt

On Thursday, November 12, 2015 at 9:23:40 AM UTC, Guanna Li wrote:
>
> I reported my test results here:
> https://groups.google.com/forum/#!topic/cp2k/UYaBsH6A7e0
>
> All single point calculations used the same input structure. But you can 
> see the enerny didn't converge even the CUTOFF value is big. 
>  
>
> On Monday, November 9, 2015 at 4:33:32 PM UTC+1, 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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