Is there a way to disable the automatic usage of ECPs? I can only think of manually specifying a basis set definition without the ECP terms, but is kind of wasteful for built-in sets. Could BasisSet be manipulated?
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Basis sets designed to use ECP for certain elements won’t give sensible answers with only the non-ECP parts present. In particular the def2 basis usually have ECP for >Kr. There are a few bases that are all-electron for the heavy elements; Psi4 only defines sto-3g and 3-21g past Kr, I think.
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Now that X2C is in Psi4, it might make sense to try and grab the Dyall basis sets from DIRAC.
http://dirac.chem.sdu.dk/basisarchives/dyall/
The nasty thing is that they’re not in an easily readable format…