Abstract: Melamine (C₃H₆N₆) is an industrial raw material that is extremely harmful to the human body. It is listed as a carcinogen by the World Health Organization. It is particularly important to study its properties under external electric field. In this paper, we have studied the changes of bond length, total energy, dipole moment (induced dipole moment), lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO) energy gap, Infrared spectroscopy, and dissociation potential energy of C₃H₆N₆ using density functional theory (DFT) at the B3PW91/6-31+ (d, p) basis set level. By calculating the stable electronic structure of the C₃H₆N₆ under external electric fields, the results show that when an electric field is applied in the direction of the N-C bond, the total energy of the C₃H₆N₆ decreases, the dipole moment increases with the increases of the strength of external electric field gradually. On the contrary, the energy gap decreased with the increase of the strength of external field. The electric field has different effects on different bond lengths. As the external electric field gradually increases, the bond length of different N-C bonds changes differently, and the N-H bond length gradually decreases.

Key words: C₃H₆N₆, DFT, external electric field, infrared spectrum