“…The CASSCF/XMCQDPT strategy shows good results for the treatment of the photosynthetic chromophores: bacteriochlorophylls, 40 chlorophylls, 41 and carotenoids. 42 The excitonic couplings calculated based on the CASSCF wave function and excitation energies calculated by CASSCF/XMCQDPT give rather good excitonic Hamiltonians for the modeling of the excitation energy transfer in photosynthesis. 6,9 Fragment-based NOCI was in the similar way improved by PT corrections calculated by CASPT2, NEVPT2, and DCD-CAS.…”