Because we do not know how to compute the S 2 value in DFT, we should formulate this question -whether or not we have unphysical symmetry breaking -in terms of finding molecular properties that could report on it. The same concerns apply to spatial symmetry breaking. One example of how one may approach this problem is a charge-transfer system, such as (He) + 3 or the charged ethylene dimer. Charge localization is very sensitive to Hartree-Fock-like symmetry breaking and also to the SIE. The comparison of charge localization patterns against high-level reference data can inform us whether symmetry breaking is real or artificial; some useful examples can be found in ref. 415.