ACN has been modelled using general force fields that mimic a range of organic solvents, or by potential functions that are specifically tailored to ACN. These e↵orts have been reviewed elsewhere. The most commonly used force fields are based on fixed point charges for describing the electrostatic interactions in such a way as to reproduce properties of the condensed phases, in particular the liquid, but do not include a representation of the intramolecular polarization. Solvent polarization is known to have a large impact on e.g. electronic excitations of solvated molecules. The single-center multipole expansion (SCME) is based on a di↵erent approach. Instead of using point charges, the electrostatics are represented using the multipole expansion around a single center on each molecule.