The electron (de)excitation process occurs rapidly, while the relaxation (reorganization) of solvent molecules is relatively slow. When both the electron and molecular configurations are fully relaxed in a given state, this is referred to as the equilibrium regime. However, the geometrical relaxation of solvent molecules does not happen instantaneously and cannot keep pace with the absorption or emission processes. To account for the different timescales, we separate the fast and slow components: only the fast component responds to the (de)excited state, while the slow component is constructed using the reaction field of the initial state. This situation is described as a nonequilibrium regime.