[CP2K-user] [CP2K:18661] About cutoff benchmarking in Cerium(III) chloride

[Aditya Goyal]

Hi Lucas, 
Thanks for the response. 
I'm using DZVP-MOLOPT-SR-GTH for Ce with 12 electrons (-q12). In my 
calculations, I tried cut-off energies of 200, 250, 300, ...... till 1000 
Ry (at REL_CUTOFF= 60 Ry and 100 Ry). However, I mentioned only a few of 
them in the original query.
So, I didn't find energy convergence near 260 Ry and above (see original 
query). I'm not using any smoother (XC_GRID section) in my calculation. 
Would you recommend some other changes in the parameters?

Regards
Aditya


On Tuesday, April 11, 2023 at 11:16:29 PM UTC+5:30 Lucas Lodeiro wrote:

> Hello Aditya,
>
> It is not clear what basis set you are using, since there are two 
> DZVP-MOLOPT-SR-GTH for Ce, one with 12 electrons (-q12) and another with 30 
> electrons (-q30).
> In my experience the best approach to know a cutoff estimate is from the 
> HIGHER_COEFFICIENT in the whole basis set. Taking the result from 
> HIGHER_COEFFICIENT*REL_CUTOFF you can get an approximate CUTOFF for 
> convergence.
> From BASIS_MOLOPT_UCL file, the DZVP-MOLOPT-SR-GTH-q12 basis set has 
> a  HIGHER_COEFFICIENT of 4.348 and DZVP-MOLOPT-SR-GTH-q30  basis set has 
> a  HIGHER_COEFFICIENT of 18.922, so with a REL_CUTOFF of 60Ry, the 
> convergence must be reached at 260Ry and 1135Ry respectively.
> Also, if you are using smoothers (XC_GRID section), the convergence test 
> behavior will not be as expected, with a monotonous convergence... in my 
> experience always show more oscillations...
> A last thing, the EPS_DEFAULT and EPS_SCF values are important to reach a 
> good CUTOFF convergence, values of 1E-12 and 1E-06, respectively, are 
> usually good.
>
> Regards - Lucas
>
> El mar, 11 abr 2023 a las 3:33, Aditya Goyal (<goyal.a... at gmail.com>) 
> escribió:
>
>> Dear CP2K users,
>> I'm trying to simulate a molten cerium chloride system with 40CeCl3 
>> molecules. Before performing any extensive calculation, I'm trying to 
>> benchmark the cutoff energy used in the DFT section by performing 
>> single-point energy calculations. I'm using DZVP basis sets for Ce & Cl 
>> with PBE functional by taking 800 Ry as a benchmark for comparison. 
>>
>> For a Relative cutoff of 60 Ry 
>> Cutoff          Energy(Ha)               Delta E (kJ/mol) wrt. 800 Ry
>> 350 Ry -3357.32389476218      3.61119311934135
>> 550 Ry -3357.3063307436 <(306)%20330-7436>      49.7255239006927
>> 600 Ry -3357.27607335904     129.166287063426
>> 650 Ry -3357.28237568966     112.619518020088
>> 700 Ry -3357.31280473755      32.7280527853891
>> 750 Ry -3357.31982535559      14.2954201205428
>> 800 Ry -3357.32527019281       0.00000000000000
>>
>> Similarly, For a Relative cutoff of 100 Ry
>> Cutoff          Energy(Ha)               Delta E (kJ/mol) wrt. 800 Ry
>> 350 Ry -3357.31559413633    -49.9141589061937
>> 550 Ry -3357.3107413093 <(310)%20741-3093>    -37.1730615379035
>> 600 Ry -3357.29750596273      -2.42365911922866
>> 650 Ry -3357.33819509308    -109.252970852155
>> 700 Ry -3357.32224091494     -67.3652761456795
>> 750 Ry -3357.30040482541     -10.0346230856023
>> 800 Ry -3357.29658283985      0.00000000000000
>>
>> So, I'm not finding a convergence of energy or any particular trend at 
>> any cutoff (for both relative cutoff cases). Can anyone suggest some 
>> parameter changes that may be used to achieve convergence? Any help would 
>> be appreciated. 
>>
>> Regards
>> Aditya
>>
>>
>>
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>>
>

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