Using Gaussian and Orca, UV and fluorescence spectra of three amino acids (Tyr: Tyrosine, Trp: Tryptophan, Phe: Phenylalanine) were calculated by different functionals (B3LYP, BP86, wB97X). The spectra calculated by BP86 are consistent with the experiments. UV spectra peak of Tyr is 255 nm (Exp. 275 nm, Δλ = 20 nm), Trp is 279 nm (Exp. 277 nm, Δλ = 2 nm), and Phe is 275 nm (Exp. 257 nm, Δλ = 18 nm). Fluorescence spectra peak of Trp is 341 nm (Exp. 350 nm, Δλ = 9 nm), Tyr is 295 nm (Exp. 306 nm, Δλ = 11 nm), and Phe is 285 nm (Exp. 302 nm, Δλ = 17 nm). Moreover, a theoretical model for calculating the excited states of biomolecules is established. Compared with Gaussian's results, Orca is more quickly and effectively for calculating excited state spectra with the same accuracy.
Keywords: Amino acids; DFT; Excitation spectra; Orca.