The cc-pV5Z-F12 basis set: reaching the basis set limit in explicitly   correlated calculations
  We have developed and benchmarked a new extended basis set for explicitly correlated calculations, namely cc-pV5Z-F12. It is offered in two variants, cc-pV5Z-F12 and cc- pV5Z-F12(rev2), the latter of which has additional basis functions on hydrogen not present in the cc-pVnZ-F12 (n=D,T,Q) sequence.A large uncontracted 'reference' basis set is used for benchmarking. cc-pVnZ-F12 (n=D, T, Q, 5) is shown to be a convergent hierarchy. Especially the cc- pV5Z-F12(rev2) basis set can yield the valence CCSD component of total atomization energies (TAEs), without any extrapolation, to an accuracy normally associated with aug-cc-pV{5,6}Z extrapolations. SCF components are functionally at the basis set limit, while the MP2 limit can be approached to as little as 0.01 kcal/mol without extrapolation. The determination of (T) appears to be the most difficult of the three components and cannot presently be accomplished without extrapolation or scaling. (T) extrapolation from cc-pV{T,Q}Z-F12 basis sets, combined with CCSD-F12b/cc-pV5Z-F12 calculations appears to be an accurate combination for explicitly correlated thermochemistry. For accurate work on noncovalent interactions, basis set superposition error with the cc-pV5Z-F12 basis set is shown to be so small that counterpoise corrections can be neglected for all but the most exacting purposes. 
Kirk A. Peterson, Manoj Kumar Kesharwani, and Jan M. L. Martin
physics.chem-ph physics.comp-ph