In Defense of (Certain) Pople-Type Basis Sets
Comments
This kind of paper really frustrates me. Sure, I would agree with the starting premise: sweeping "bans" of a whole class of basis sets are unwarranted (it is really 6-31G* we would like to see less of). And it seems like the authors would go on to a well-devised analysis. They set up with "Our assessment includes def2-QZVPD, which should lie near the basis-set limit and establishes the inherent accuracy of each functional." OK, so they know there is an inherent error in the functional and will not be fooled by error cancellation, right? No - they then go on to stress how some of the Pople basis sets have a smaller std. dev. than some of the Karlsruhe ones: "In particular, 6-311+G(2df,p) reduces the standard deviation of the errors by 2 kcal/mol, relative to def2-TZVP, for the meta-generalized gradient approximations (mGGAs), a significant improvement that is not adequately reflected in the median absolute errors." The numbers here are: std. dev. | B3LYP | M06-2X | wB97M-V 6-311+G(2df,p) | 9.0 | 5.5 | 5.1 def2-TZVP | 10.0 | 7.6 | 7.2 def2-QZVPD | 9.6 | 8.1 | 7.3 So what they are saying is true, but 6-311+G(2df,p) also gives a smaller std. dev. than def2-QZVPD - which they said was close to the CBS limit. How can they fail to discuss this?! At this point the whole argument loses credibility for me...