Abstract: Based on the M06-2X theoretical method, the electronic excitation was calculated by time-dependent density functional theory (TDDFT) at the level of the aug-cc-pVTZ base group with dispersion function, we gave the isosurface diagrams of hole-electron, natural transition orbit (NTO) and charge density difference (CDD) of the first elementary reaction intermediate INT₁-S-Met-CHCl₃+H₂O molecular system in the chiral transition of the Met(methionine)+H₂O composite system under implicit solvent chloroform, and analyzed the properties and electronic structure of the excited states of the intermediates. The results show that: H atoms migrate to form intermediates, resulting in significant changes in the structure of Met molecular system, based on NTO, hole-electron and CDD isosurfaces, the mutual recognition of excitation types of excited states of INT₁-S-Met-CHCl₃+H₂O molecular system is consistent with the hole-electron data analysis.

Key words: methionine, first elementary reaction, composite system, hole-electron, electronic excitation