For small molecules, transition densities are often (but certainly not always) dominated by a principal pair of NTOs, and long-range electron-transfer excitations fall into this category. In this special case, non-invariant metrics ∆r, ∆σ, and Γ are stable and interpretable in terms of expectation values when evaluated in the NTO representation. Under these circumstances, (∆r) NTO does measure electron-hole separation and Γ NTO = (∆r) NTO + (∆σ) NTO (25) measures overall charge displacement including any size disparity between the excited electron and the hole, which is measured by (∆σ) NTO . However, it is easy to find molecules where many of the excited states cannot be described by a single pair of NTOs. In such cases, interpretability of (∆r) NTO , (∆σ) NTO , and Γ NTO is lost.