Novel approach to excited-state calculations of large molecules based on divide-and-conquer method: application to photoactive yellow protein.

In this study, the divide-and-conquer (DC) method is extended to configuration-interaction singles, time-dependent density functional, and symmetry-adapted cluster configuration interaction (SACCI) theories for enabling excited-state calculations of large systems. In DC-based excited-state theories, one subsystem is selected as the excitation subsystem and analyzed via excited-state calculations. Test calculations for formaldehyde in water and a conjugated aldehyde demonstrate the high accuracy and effectiveness of these methods. To demonstrate the efficiency of the method, we calculated the π-π* excited state of photoactive yellow protein (PYP). The numerical applications to PYP confirm that the DC-SACCI method significantly accelerates the excited-state calculations while maintaining high accuracy.