To achieve a high transferability of CG models, their energy potential functions of CG models are usually defined in a way similar to the AA force fields. The parameters in the CG force fields were developed by combining both of the aforementioned approaches. For example, the Martini protein force fields contain bonded and non-bonded interactions. Its bonding interaction parameters of Martini CG particles were derived using "top-down" fitting of structural data of proteins, while the Lennard-Jones (LJ) parameters of CG particles for vdW interactions were derived using "bottom-up" fitting based on the OPLS AA simulation data.