Since CV is a cationic organic dye, the influence of a chloride counterion on the system dynamics and computed spectra was also considered. For this purpose, CV together with a Cl -ion was solvated in a sphere, containing 1887 methanol molecules, with the counterion initialized as a contact ion pair with CV. A static FF for CV likely does not yield a correct description of the electrostatic interactions with the Cl -ion, as DFT calculations in vacuum reveal a significant redistribution of electronic charge on the N atoms to stabilize a contact ion pairing (see SI Sec. 7). Thus, the MM equilibration step was skipped and a pure 77 ps QM/MM simulation was performed for CV with the ion in methanol, with only the CV molecule treated at the QM level. The first 41 ps were discarded to allow for an equilibration of the chromophore-ion configuration (see SI Sec. 4), generating 36 ps of usable trajectory. Since interactions between CV and the Cl -were expected to be weak due to the polar nature of methanol solvent environment, only a single trajectory was generated explicitly including the counterion.