Ultra-Fast Computation of Excited-States Spectra for Large Systems: Ultraviolet and Fluorescence Spectra of Proteins

A workable approach named xTB-sTDDFT was selected to investigate the excited-state spectra of oxytocin (135 atoms), GHRP-6 (120 atoms) and insulin (793 atoms). Three different Hartree-Fock components functionals (wB97XD3: 51%, LC-BLYP: 53%, wB97X: 57%) were used to calculate the excitation spectra, and the results calculated by wB97XD3 functional well agree with the experiments. It's a deep impression that computed time cost reduced by more than 80%. For polypeptide (oxytocin and GHRP-6), both UV and fluorescence spectra were obtained, and the errors between the calculated and experimental values approximately were 20 nm. For Insulin, the errors are within 15 nm. UV spectrum peak is lambda(cal) = 262 nm (lambda(exp) = 277 nm, Delta lambda = 15 nm), and fluorescence spectrum peak is lambda(cal) = 294 nm (lambda(exp) = 304 nm, Delta lambda = 10 nm). In summary, a suitable theoretical model is established to ultra-fast calculate the electronic excitation spectra of large systems, such as proteins and biomacromolecules, with good calculation accuracy, fast calculation speed and low cost.