I find this formula in an article I do not know what is the point? and how to apply?
The corresponding rate constants have been calculated using
the transition-state theory (TST) at the CCSD(T)/6-31G(d) + CF//B3LYP/6-311+G(d,p) level of theory."
Thanks to all of you in advance
That is not G4MP2 and not even part of it, while G4MP2 uses smaller basis set for optimisation.
Yes, that is two step calculation, with single point CCSD(T) over structure optimised on B3LYP/6-311+G(d,p). What i cannot say is what "+CF" mean.
UpD. I found the paper, it is "Ab initio investigation of O3 addition to double bonds of limonene" and computational details are described rather well in it. I will just cite the second part:
" The DFT structures were then used in the single-point energy ab initio calculations using frozen core second-order Møller–Plesset perturbation theory (MP2) and coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations (CCSD(T) with various basis sets. For more accurate single-point energy, the basis set effects on calculated energies for O3-limonene reactions were corrected at MP2 level according to the recently developed method, which have been employed by studying the complex reaction mechanisms and pathways of volatile organic compounds (VOCs) in the atmosphere [27]. A correction factor (CF) was determined from the energy difference between the MP2/6-31G(d) and MP2/6-311++G(d,p) levels. The values of calculated energies at the CCSD(T)/6-31G(d) level were then corrected by the MP2 level correction factors, corresponding to the CCSD(T)/6-31G(d) + CF method. "
So yes, there is some similarity to G4MP2 approach, like accounting of ZPE and extrapolation of MP2 component to basis set limit, but also with other basis sets. Also no HF energy correction was used. In total this approach looks rather suspicious to me and values discussed in the paper (below 1 kcal/mol) also are quite risky. There are many assumptions in this strategy as well as in G* methods, starting from the guess that CCSD(T) and MP2 would has same difference between 6-31G and 6-311++G(d,p) that is expected to be closed to CBS limit. Instead of G* approaches i would use DLPNO-CCSD(T) with big basis set nowadays.
Dear Dmitry Sharapa,
I found it in the paper (attached). and "CF" it is a correction factor.
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