Fragment molecular orbital calculations for excitation energies of blue- and yellow-fluorescent proteins

► The excitation energy of yellow-fluorescent protein (YFP) was evaluated by using the modified versions of configuration interaction singles and perturbative doubles (CIS(D)) in conjunction with the fragment molecular orbital (FMO) scheme. ► It is known that the pigment moiety of YFP is located at the center of β-barrel structure and it has a π-stacking interaction with Tyr203. ► Our best estimate with the second-order self-energy shift was obtained as 2.53 eV being comparable to the experimental value of 2.41 eV.