Figure 4. Example: the variation method is used to determine energies of
coupled excited states (ε1-4 and ε*1-4)
of the Fenna-Matthews-Olson light-harvesting complex (shown in shown in
the inset). The method helps to determine major contributions of
uncoupled localized excitations of bacteriochlorophyll molecules (BCL
401-407) to the coupled states. Reproduced from Ref. 2.