Empirical force field for the simulation of a class of chromophores in a photosynthetic center

We present the results of the parametrization of the AMBER molecular mechanical force field for simulating Bacteriochlorophylls (BChls) and Bacteriopheophytins (BPhs). Ab initio Density Functional Theory (DFT) calculations on fragments and the entire chromophores in their gas-phase have been used to obtain a new set of force field parameters which are able to reproduce static properties and vibrational frequencies of the chromophores. Molecular dynamics (MD) simulations of crystalline BPh and BChl have been performed to test our intramolecular parameterization as well as the non-bonded parameters.