Abstract: Using the CAMB3LYP method of density functional theory, we optimized the geometric configuration of S-phenylalanine (S-Phe) molecule at 6-31G(d) basis set under different conditions. The results show that, under the conditions of implicit methanol solvent and the gas phase,  the qualitative results of charge transfer in S-Phe molecular system are basically consistent, the quantitative results are slightly different, the S2 excited states of each fragment are basically consistent, only the difference of S2 excited state of COOH fragment is 2.2%, and the difference of S4 excited state is 0.4%—2.8%. The qualitative analysis lacks an S5 excited state in different environments. The difference of charge transfer of S2 and S4 excited states calculated by Becke method is about 2.5%—8%.

Key words: phenylalanine, natural transition orbit (NTO), charge , transfer, orbital fragment