Q y -Shift J coupl/eV J coupl/cm -1 1 to 2/eV osc. str. Table : Coulomb coupling, transitions from the ground to the first and second excitonic states with the corresponding oscillator strengths along with the slip angle θ for BChl models in which the upper monomer is shifted 6.5 Å along the Z-axis and sliding along Q y (in Å).