Fragment molecular orbital calculations on red fluorescent protein (DsRed)

Graphic representation of DsRed (the first monomer of '1ZGO' in PDB). The pigment moiety located at the center of barrel is drawn with spheres. The excitation energy and emission energy of this system are evaluated by the recently developed approach of configuration interaction singles with perturbative doubles in conjunction with multilayer fragment molecular orbital scheme (MLFMO-CIS(D)). The best calculated results of 2.28 eV for the former and 2.21 eV for the latter are in good agreement with the corresponding experimental values of 2.22 eV and 2.13 eV.