Basis sets are not the most inspiring topic but you can't get around them. That is why we looked at them in our new paper. I am not discussing how many ζ you need or how many diffuse and polarization functions but I am asking a more subtle question: how big are the differences between basis sets of the same formal type?
This question is addressed in our new paper "Detailed Wave Function Analysis for Multireference Methods: Implementation in the Molcas Program Package and Applications to Tetracene" [full text] that appeared in JCTC. The initial purpose of this paper was to introduce a new toolbox for analyzing multireference computations in the opensource OpenMolcas program package, and I want to encourage people to use this code.
But there is also an important take home message: basis sets of the same formal type (in this case polarized doubleζ) can perform vastly different. And this is not only reflected in the energies but also seen in the densities and overall wavefunctions. In the present case, an atomic natural orbital type basis set had a particularly good performance. This good performance comes at the cost of more primitive basis functions. But these primitive basis functions only play a role in the initial AO integral computations and do not affect the cost of the actual CASSCF/CASPT2 computation at all.
Atom_mapper: determining atom correspondence between reactants and products

Many TS search algorithms interpolate between reactants and products and
require that the atom order is identical. This is time consuming to enforce
by han...
6 days ago