[CP2K-user] SCF convergence problem with large basis sets

Tom Braeckevelt tom.bra... at ugent.be
Mon Jul 5 11:44:49 UTC 2021

Dear CP2K users/developers,

I was performing some benchmarks related to the basis set size (with simply 
PBE-D3). In particular, I was checking the energy difference between 
benzene adsorbed in the H-SSZ-13 zeolite and its protonated counterpart. 
While I can see a steady improvement going from DZVP -> TZVP -> TZV2P 
(without any issue in the calculation) I encountered large problems in the 
SCF convergence when using even larger basis sets, like the QZV2(or 3)P and 
the augmented basis sets. At this point, I was only able to converge a 
couple calculations with the QZV3P using the CG optimizer (normally I use 
the DIIS) and the FULL_KINETIC preconditioner (I normally use the 
FULL_SINGLE_INVERSE), which according to the manual should be more robust. 
I also tried the diagonalization method instead of the OT one but also in 
that case the scf was not converging.
The problem is that even with the two converged calculations the energy 
difference between the two species I'm studying results to be ~3000kJ/mol 
vs the expected ~100kJ/mol, thus it looks like the two scf have converged 
to different minima.

Does anybody know how to robustly converge the scf with large basis sets? 
In attachment the input and output of the supposedly converged calculations.

Thank you in advance,
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