Generalized Energy-Based Fragmentation Approach for Localized Excited States of Large Systems.

We have extended the generalized energy-based fragmentation (GEBF) approach to localized excited states of large systems. In this approach, the excited-state energy of a large system could be expressed as the combination of the excited-state energies of "active subsystems", which contains the chromophore center, and the ground-state energies of "inactive subsystems". The GEBF approach has been implemented at the levels of time-dependent density functional theory (TDDFT) and approximate coupled cluster singles and doubles (CC2) method. Our results show that GEBF-TDDFT can reproduce the TDDFT excitation energies and solvatochromic shifts for large systems and that GEBF-CC2 could be used to validate GEBF-TDDFT result (with different functionals). The GEBF-TDDFT method is found to be able to provide satisfactory or reasonable descriptions on the experimental solvatochromic shifts for the n → π* transitions of acetone in various solutions, and the lowest π → π* transitions of pyridine and uracil in aqueous solutions.