Here, we use a hybrid active orbital selection strategy where CNTOs are used for the occupied orbital space and projected atomic orbitals (PAOs) 72 on the five central water molecules determine the virtual orbital space. In the present MLCC calculations, the active orbital space contains 25 occupied and 245 virtual orbitals. A detailed description of the orbital selection procedure with CNTOs and PAOs for the MLCC models can be found in Ref. 73.