The generalized DMET scheme and the eo-TDA method introduced above offer a "top-down" approach to understanding the effects of chromophore-solvent orbital entanglement on excitation energies. In this section, we utilize a "bottom-up" alternative based on absolutely localized molecular orbitals (ALMOs) to demonstrate the orbital entanglement effects from a different perspective. Specifically, we employ ALMO-TDA calculations with varying active spaces to assess how the excitations on solvent molecules, as well as the chromophore→solvent and solvent→chromophore charge-transfer excitations impact the S 1 excitation energy of the chromophore when these excitations are superimposed. The ALMO-TDA method, which is the TDDFT/TDA extension of the ALMO-CIS method, was originally proposed to calculate the absorption spectra of large molecular clusters. This method The top row (A) shows the transitions between occupied (O) and virtual (V) orbitals involved in the ALMO-TDA model that gives the results in panels (B) and (C) below, where "C" and "S" denote chromophore and solvent molecules, respectively. In panels (B) and (C), the excitation energies (100 frames for each chromophore) obtained from ALMO-TDA calculations with different active spaces are plotted against the the full-system TDDFT/TDA excitation energies. The root-mean-square deviations (RMSD) and the R 2 values from linear fitting are reported. The ALMO-TDA and full-system TDA calculations were performed at the ωB97X-D/6-31G(d,p) level.