First principle study of proton transfer in the green fluorescent protein (GFP): Ab initio PES in a cluster model

In this paper we perform high level complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations to generate three-dimensional potential energy surfaces for the proton chain transfer in the green fluorescent protein (GFP) based on a minimal quantum mechanical cluster model. Both the electronic ground state and the first excited state are considered within an approximate rigid model. We focus on the energetic terms of the proton transfers in this paper, and the exact quantum dynamics simulations for proton transfer on the ground and excited states will be reported later. Our results from MRCI quantum mechanical calculations are contrasted with those of other computational studies using both CASPT2 method and DFT method, and are compared with the experimental findings for GFP in the full protein environment.