Here, C is the matrix of ECI coefficients (coefficients of the full-system states written in the ECI basis), while the diagonal matrix E contains their energies. Note that there is no overlap matrix between ECSFs, since the SOA implies their (full) orthogonality. Depending on how strongly the chromophores are interacting in the system, the ECI vectors can be more or less "correlated". For example, if the individual ECSFs are already good approximations of the full-system states, the ECI coefficient of the leading ECSF will be very dominant (e.g., ≈ ±0.99) for each state. For systems with symmetry-equivalent fragments, one will usually find several symmetry-equivalent ECSFs with (up to sign) equal contributions, whose sum of squares is approximately 1. Such states dominated by one ECSF (or set of symmetryequivalent ECSFs) are expected to occur in systems with weakly coupled fragments. On the other hand, if the individual ECSFs are not good approximations of the full-system states, each ECI vector will have a large number of nonnegligible coefficients, i.e., a substantial "excitonic correlation" can be expected. In this case, one could speak of a strongly coupled multichromophoric systems.