Energy-based fragmentation contribution approach for calculating the fluorescence spectrum of biomacromolecules

It remains challenging to calculate the fluorescence spectra of biomacromolecules due to the large number of atoms involved. Here, we propose an efficient computation method, named the energy-based fragmentation contribution (EBFC) approach, to calculate the fluorescence spectra of super-large proteins. Specifically, an optimized molecular tailoring rule is provided to divide a super-large protein into smaller fragments, then the extended tight binding method and the simplified time-dependent density functional theory approach are employed to calculate the fluorescence spectrum of each fragment in parallel, and finally, the fluorescence spectrum of the target protein is obtained by superimposing the contributions of all fragments. Utilizing the EBFC approach, we calculated fluorescence spectra of three different super-large proteins and the calculated spectra show excellent agreement with experimental data with the difference of less than 1.5%. This work provides an efficient and reliable approach to enhance the modeling capability of the excited states in biomacromolecules.