The effects of the environment on the chromophore are modeled using the PE model, which we briefly described in the introduction. We investigate the ground-state dipole moment and the excitation energy of the lowest singlet transition together with the associated one-and two-photon absorption strengths. These properties were computed using the CAM- B3LYP exchange-correlation functional and the pcseg-2 basis set. Effective external field (EEF) effects were included in the computation of absorption strengths. The properties were calculated using the Dalton program 41,42 employing PElib 74 and Gen1Int. The reference properties are calculated using the MFCC-based M2P2 potential to describe the protein surroundings which has been shown to be highly accurate. The M2P2 potential consists of atom-centered multipoles up to quadrupoles and atom-centered anisotropic dipole-dipole polarizabilities. In this work, the multipoles and polarizabilities were computed at PBE0/augx-cc-pVDZ level of theory using the LoProp approach 8 to distribute the multipoles and polarizabilities to atomic centers which thus matches the level of theory used to derive the CP 3 parameters. We benchmark properties obtained from calculations where the whole protein is modeled by the CP 3 as well as mixed intermediates where the residues closest to the chromophore (according to a distance criterion) are described by the more accurate M2P2 potential and the remainder by the CP 3 . All water molecules and ions were in all cases described by the solvent embedding potential (SEP) which consist of charges and isotropic dipole-dipole polarizabilities. The PyFraME package was used to generate the potentials employing the Dalton program 41,42 and the LoProp for Dalton script for the individual fragment calculations.