Avoiding numerical instabilities in R12 calculations through universal R12 consistent basis sets

We show that the incidental numerical instabilities in explicitly correlated coupled cluster R12 (CC-R12) calculations can be a priori removed by using systematically developed R12 suited basis sets. Those are quite different from basis sets developed for conventional calculations mainly in polarization functions. Using even tempered polarization sets for carbon and oxygen we were able to define compromise R12 suited bases which describe equally well atomic ground states, positive and negative ions and electric field polarized atoms. Corresponding energies obtained with such ‘R12 universal’ sets remain accurate to within a few μEh with respect to the ‘R12 optimal’ bases of individual systems.