One typical approach to overcome the computational scaling when considering QM calculations on big systems is to apply hybrid quantum-classical methods, where the system of interest is divided into subsystems. Here, the central part of the system (e.g. a chromophore) is treated with QM while the surroundings are treated as either a dielectric polarizable medium or with a molecular mechanics (MM) based method, which allows much larger systems to be investigated. The clear advantage of the latter approach is that the structural details of the environment are preserved. The balance between computational cost versus adequate precision necessitates new models to be developed to imitate the surroundings in a fashion where accuracy and computational cost are balanced at the appropriate level depending on the questions to be answered.