At the same time, this observation suggests that correspondences between proper expectation values and the numerical values of (∆r) NTO , (∆σ) NTO , and Γ NTO may degrade in cases where more than one principal NTO pair is significant (i.e., λ 2 2 0). Such cases will be examined in Section 4 .3. Before that, we consider the use of Γ and Λ for their original purpose: detecting errors in TD-DFT excitation energies by correlating those errors with a measure of CT character.