Once extrapolated, the GTO CBS estimates follow a similar trend with larger (absolute) differences attributed to larger numbers of electrons (N e ) (Fig. and Fig. ), thus questioning the agreement between GTOs and PWs in the limit of (very) large systems. Note that such a difference applies to all promising extrapolations found in this work (Fig. and). The reasons can be multiple, and arise from a combination of the BSSE, the accuracy of the extrapolation scheme, and the intrinsic nature of the basis functions. Nevertheless, as observed earlier (Section IV B), the CP correction seems adequate to eliminate the BSSE so that the last two factors will dominate, which are directly linked to the BSIE. Let us recall that the initial motivation behind the extrapolation schemes is to cope with the electron-electron cusp that hampers the basis set convergence . Therefore, although not firmly established by our results, the fact that extrapolated energies deviate from PWs could indicate a residual completeness mismatch between GTOs and PWs in the limit of large systems, originating rather from an in(over)complete description of the wave function to capture the long-range (polarization, dispersion) contributions to the correlation energy. This encourages further comparison of atom-centered bases against other basis sets, either explicitly correlated, plane waves or purely numerical, in the calculation of correlation energies of large systems.