We modeled excitation energy transfer (EET) in the peridinin-chlorophyll a-protein (PCP) complex of dinoflagellate Amphidinium carterae to determine which pathways contribute dominantly to the high efficiency of this process. We used complete active space configuration interaction (CAS-CI) to calculate electronic structure properties of the peridinin (Pm) and chlorophyll a (CLA) pigments in PCP and the transition density cube (TDC) method to calculate Coulombic couplings between energy transfer donors and acceptors. Our calculations show that the S-1 -> Q(y) EET pathway from peridinin to chlorophyll a is the dominant energy transfer pathway in PCP, with two sets of interactions-between PID612 and CLA601 and between PID622 and CLA602-contributing most strongly. EET lifetimes for these two interactions were calculated to be 2.66 and 2.90, with quantum efficiencies of 85.75 and 84.65%, respectively. The calculated Coulombic couplings for EET between two peridinin molecules in the strongly allowed S-2 excited states are extremely large and suggest excitonic coupling between pairs of peridinin S-2 states. This methodology is also broadly applicable to the study of EET in other photosynthetic complexes and/or organic photovoltaics, where both single and double excitations are present and donor and acceptor molecules are tightly packed.