Dear professor Hutter,<div>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?</div><div>Kind regards,</div><div><br /></div><div>Riccardo Pezzetta<br /><br /></div><div class="gmail_quote"><div dir="auto" class="gmail_attr">Il giorno giovedì 2 aprile 2026 alle 09:41:01 UTC+2 Jürg Hutter ha scritto:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi
<br>
<br>the syntax for defining a basis set is
<br>
<br>BASIS "TYPE" "NAME"
<br>
<br>If "TYPE" is missing it defaults to ORB. If there is more than one BASIS definition for ORB
<br>the basis sets are combined (e.g. allowing to augment a standard basis with a difuse set).
<br>
<br>Your second input therefore was combining the two basis sets to create a huge ORB basis
<br>and then used a an automatic procedure to generate a RI basis based on this huge ORB set.
<br>
<br>regards
<br>JH
<br>
<br>________________________________________
<br>From: <a href data-email-masked rel="nofollow">cp...@googlegroups.com</a> <<a href data-email-masked rel="nofollow">cp...@googlegroups.com</a>> on behalf of Riccardo Pezzetta <<a href data-email-masked rel="nofollow">richi...@gmail.com</a>>
<br>Sent: Wednesday, April 1, 2026 4:09 PM
<br>To: cp2k
<br>Subject: [CP2K:22149] Choice of RI basis set fo RPA calculation of argon dimer
<br>
<br>Dear CP2K community,
<br>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:
<br>BASIS_SET TZV2P-MOLOPT-PBE-GTH-q8
<br>BASIS_SET RI_AUX RI_85_7_6_5_5_0_0_0_8.0e-08
<br>
<br>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:
<br>BASIS_SET TZV2P-MOLOPT-PBE-GTH-q8
<br>BASIS_SET RI_85_7_6_5_5_0_0_0_8.0e-08
<br>
<br>With these parameters i read in the output file:
<br>Orbital Basis Set RI_85_7_6_5_5_0_0_0_8.0e-08TZV2P-MOLOPT-
<br>and
<br>RI Auxiliary Basis Set Ar-RI-AUX-RI_85_7_6_5_5_0_0_0_8.0e-08TZV
<br>
<br>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.
<br>Thank you in advance.
<br>Kind regards,
<br>
<br>Riccardo Pezzetta
<br>
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