The right panel uses GEO values to rank various approximation for the HCN structure (black line). Both sets of GEO values, the one that uses values the CCSD(T) structure (magenta) and the one that uses semiexperimental (SE) structure (blue) are virtually indistinguishable from GEO . This is the case even though GEO costs way more to compute than GEO . The use of GEO in place of GEO enables us to bypass the use of expensive CCSD(T) energies to perform the GEO analysis. For GEO we also need reference G 0 (Eq. 2), but the use of SE geometries enables us to completely by-pass input from CCSD(T) and extend the GEO analysis to molecules whose structures cannot be obtained by CCSD(T)(full) within a sufficiently large basis set. In general, GEO is energetically very close to GEO even for inaccurate methods, such as HF, 1 as the curvature of Ẽ (G) at the minimum is reasonable even for HF (compare Eqs. 6 and 7).