Abstract: Based on the optimized R-threonine (R-Thr) molecular structure, the method of the time-dependent density functional theory (TDDFT) was used to calculate the wave functions of excited states in the process of electronic excitation of R-Thr molecular system in gas phase, implicit H₂O and methanol solvents at the PBE0/def2-TZVP， and the excitation types of valence shell electrons in R-Thr mol-ecular system was studied by identifying the molecular orbital type method. The results show that the implicit solvent environment is more suitable for studying the electronic excitation characteristics of R-Thr molecular system than the gas\|phase environment, and the analysis results of molecular orbital (MO)  type and the Δr index are ideal, most excitation types of excited states are in good agreement with excitatin mode identification.

Key words: threonine, electronic excitation, molecular orbital (MO) type, implicit solvent