As an alternative to cope with the BSIE, explicitly correlated methods (e.g. MP2-R12/F12) are particularly suited for fast convergence of correlation energies due to their correlating n-electron basis functions that depend explicitly on the interelectronic coordinates r 12 . R12 or F12 refers to whether the explicit two-electron functions (geminals) are given by linear or Gaussian-type expressions, respectively. Apart from the wavefunction Ansatz, R12/F12 methods are similar to their standard counterparts and thus converge in theory to values very close to the CBS limit. However, such calculations are neither free of BSSE for smaller bases, nor of linear dependencies for larger molecules, and they can suffer from numerical instabilities . In addition, while recovering most of the correlation energy for a much smaller number of basis functions, they may still have difficulty incorporating the very last bits required to reach very high accuracy (≤ 0.1 kcal/mol) due to the choice of the geminal and integral approximations, such as the resolution of identity or neglect of terms, that are necessary to maintain reasonable calculation costs . For instance, a deviation of about 0.5 kcal/mol was observed between H 2 O total energies coming from different MP2-R12 approximations and a 1 kcal/mol difference was identified between different R12 basis sets . Deviations of the order of 0.1 kcal/mol were also noticed when it comes to interaction energies . Nevertheless, MP2(CCSD(T))-R12/F12 calculations have so far been the only CBS references available to assess the reliability of GTO extrapolations from the (aug-)cc-pVXZ bases .