Towards universal R12 consistent basis sets

Using H- and H-2 as examples, it is demonstrated that parameters of the one-electron basis sets optimized for explicitly correlated R12 calculations are quite different from those developed for conventional calculations that utilize a usual configuration interaction expansion for the wavefunction. Systematic development of universal R12 suited basis sets is suggested, using the even-tempered paradigm. In explicitly correlated calculations, such R12 consistent basis sets should describe the given atom in a variety of bonding situations with a few muE(h) absolute accuracy.