The MCR is the set of MCs that are included in the potential surface and the complete potential can systematically be approximated by restricting how many MCs are included in the MCR. The particular approximation may follow the logic of the n-mode representation but can also deviate from it by selecting the MCR in other ways. For example, one can in the PES follow the logic of the excitation spaces used in MR-MCTDH[n] 40 and define a vector of weights w m for each mode and include MCs in the MCR if