In toluene, CV interacts with solvent molecules through non-covalent interaction such as π-stacking. The torsion angle of the aryl rings of CV in toluene has a smaller standard deviation compared to vacuum (Table ), suggesting that bulky solvent molecules hinders rotation. When constructing the cumulant spectrum, we find that the predicted spectral lineshape for CV in pure toluene solvent has an incorrect splitting between the peaks with a value of 0.119 eV compared to the experimental value 0.256 eV considering only the above contributions (see Fig. and). Being a nonpolar solvent, toluene cannot screen the interactions between the cationic CV and its Cl -counterion, in contrast to the polar solvent methanol. This interaction, especially a close association between CV and the ion through the formation of a contact ion pair, can break the D 3 symmetry of CV. According to the ground state optimized structure of CV in the presence of a counterion in vacuum, the distance between the closest nitrogen atom to the ion and the chloride ion is 4.4 Å and this configuration yields a substantial energy difference between S 1 and S 2 transition of 0.52 eV (see Fig. ). To investigate the influence of thermal fluctuations on the position of the counterion, we perform a 8 ps AIMD trajectory of CV with the Cl -ion in vacuum. We find that the average distance between the closest nitrogen and the counterion is 4 Å along the trajectory, even less than for the optimized geometry in vacuum. The dynamic calculations again reveal a strong direct electrostatic interaction between CV and the chloride ion, leading to a large S 1 and S 2 splitting in the computed absorption lineshape in the cumulant approach, with the value of 0.57 eV (Fig. ).