A simplified approach for the coupling of excitation energy transfer

► We propose a simple method to calculate the coupling of singlet-to-singlet and triplet-to-triplet energy transfer. ► Coulomb term are the major contribution to the coupling of singlet-to-singlet energy transfer. ► Effect from the intermolecular charge-transfer states dorminates in triplet-to-triplet energy transfer. ► This method can be expanded by including correlated wavefunctions.