Excited states of biological chromophores studied using many-body perturbation theory: Effects of resonant-antiresonant coupling and dynamical screening

The excited states of model chromophores of the photoactive yellow protein and of rhodopsin are studied using ab initio many-body perturbation theory (within the GW approximation and Bethe-Salpeter equation). Calculations beyond the Tamm-Dancoff approximation, i.e., consideration of the resonant-antiresonant transition coupling, are needed for an accurate description of the lowest π→π^∗ excitations due to the large exchange interaction between the electron and hole localized in the low-dimension systems. The inclusion of dynamical effect in the electron-hole screening is important for an accurate description of the lowest n→π^∗ excitations.