[CP2K-user] [CP2K:22158] Choice of RI basis set fo RPA calculation of argon dimer

[Riccardo Pezzetta]

Dear professor Hutter,
thank you for your answer. Since the only RI basis for argon are the ones 
in the file BASIS_RI_MOLOPT, would you recommend using the  
TZV2P-MOLOPT-PBE-GTH-q8 basis set and  RI_AUX RI_85_7_6_5_5_0_0_0_8.0e-08 
basis set or a correlation consistent basis set like ccGRB-Q-q8 and an 
auxiliary basis set generated with  auto_basis? With the latter choice I 
get a worse result, but maybe it is because I have to include the basis set 
superposition error?
Kind regards,

Riccardo Pezzetta

Il giorno giovedì 2 aprile 2026 alle 09:41:01 UTC+2 Jürg Hutter ha scritto:

> Hi
>
> the syntax for defining a basis set is
>
> BASIS "TYPE" "NAME"
>
> If "TYPE" is missing it defaults to ORB. If there is more than one BASIS 
> definition for ORB
> the basis sets are combined (e.g. allowing to augment a standard basis 
> with a difuse set).
>
> Your second input therefore was combining the two basis sets to create a 
> huge ORB basis
> and then used a an automatic procedure to generate a RI basis based on 
> this huge ORB set.
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
> Riccardo Pezzetta <richi... at gmail.com>
> Sent: Wednesday, April 1, 2026 4:09 PM
> To: cp2k
> Subject: [CP2K:22149] Choice of RI basis set fo RPA calculation of argon 
> dimer
>
> Dear CP2K community,
> I am trying to calculate the binding energy of the argon dimer using RPA. 
> I used the basis set TZV2P-MOLOPT-PBE-GTH-q8 from the file BASIS_MOLOPT_UZH 
> with auxiliary basis set RI_85_7_6_5_5_0_0_0_8.0e-08 from the file 
> BASIS_RI_MOLOPT:
> BASIS_SET TZV2P-MOLOPT-PBE-GTH-q8
> BASIS_SET RI_AUX RI_85_7_6_5_5_0_0_0_8.0e-08
>
> With this basis I get -17.9 meV as binding energy. Then I tried to remove 
> RI_AUX in front of the auxiliary basis set:
> BASIS_SET TZV2P-MOLOPT-PBE-GTH-q8
> BASIS_SET RI_85_7_6_5_5_0_0_0_8.0e-08
>
> With these parameters i read in the output file:
> Orbital Basis Set RI_85_7_6_5_5_0_0_0_8.0e-08TZV2P-MOLOPT-
> and
> RI Auxiliary Basis Set Ar-RI-AUX-RI_85_7_6_5_5_0_0_0_8.0e-08TZV
>
> It seems that the program mixes the two basis sets, but I don't know how. 
> The result is -10.6 meV which is closer to the experimental value (which is 
> -12.3 meV) than the result I obtained writing RI_AUX in front of the 
> auxiliary basis set. Could anyone explain me what happens with this basis 
> mixing and tell me if the result based in this parameters is reliable? I 
> have attached to this message the input and output files.
> Thank you in advance.
> Kind regards,
>
> Riccardo Pezzetta
>
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