For covalent systems, GEO is excellently approximated by GEO and provides essentially the same information (e.g., rankings of approximations, the decomposition of the error into contributions from the errors in different structural parameters, etc.) At the same time, computing GEO is way less costly as it does not require running a single-point calculation with a high-level method, such as CCSD(T). Furthermore, if a reference geometry is derived from an experiment, we no longer need CCSD(T) at all, as for GEO we only need approximate energies at both reference and approximate geometries (Eq. 2). In practice this can be done by using accurate geometries as a starting point for a geometry optimization with an approximate method. After the convergence, one can easily calculate GEO from the differences in approximate energies from the first and last iteration of the optimization procedure.