Calculation of quasi-diabatic states within the DFT/MRCI(2) framework: the QD-DFT/MRCI(2) method

We describe a procedure for the calculation of quasi-diabatic states within the recently introduced DFT/MRCI(2) framework [J. Chem. Phys., 157, 164103 (2022)]. Based on an effective Hamiltonian formalism, the proposed procedure, which we term QD-DFT/MRCI(2), has the advantageous characteristics of being simultaneously highly efficient and effectively black box in nature, while directly yielding both quasi-diabatic potentials and wave functions of high quality. The accuracy and efficiency of the QD-DFT/MRCI(2) formalism are demonstrated via the simulation of the vibronic absorption spectra of furan and chlorophyll a.