Table 1. Total energies of electronic states in the cryptochrome active site. Energies were calculated for the cryptochrome active site model shown in Fig. 2. Geometry optimization in the electronic ground and excited states was performed with the state-averaged CASSCF and XMCQDPT-2 methods using the program Firefly⁵¹. Three electronic states were considered. The labels in the first column denote states marked in Fig. 3. The energy of the FAD^·− + W377^·+ state for the optimized GS geometry, in fact, is higher than the energy of the excited FAD^·− + W400*^·+ state, and, therefore, does not appear in the table. The calculated energies (CASSCF and XMCQDPT-2 values) of the second excited state for the GS geometry correspond to the FAD^·− + W400*^·+ state and are marked with an asterisk.

state	oxidized flavin	FAD·− + W400·+	FAD·− + W377·+
CASSCF total energies (a.u.)
GS, optimized	−3612.751899	−3612.641151	−3612.624968*
RP1, optimized	−3612.707732	−3612.670458	−3612.614731
RP1, with W377 rearrangement	−3612.705990	−3612.665373	−3612.622435
RP2, optimized	−3612.708593	−3612.638732	−3612.657125
XMCQDPT-2 total energies (a.u.)
GS, optimized	−3623.670253	−3623.550927	−3623.524985*
RP1, optimized	−3623.660373	−3623.596712	−3623.548341
RP1, with W377 rearrangement	−3623.651291	−3623.593714	−3623.559870
RP2, optimized	−3623.653140	−3623.573561	−3623.587278