By setting different electric fields and adopting density functional B3P86/cc PV5Z method, the geometric structure of NH molecule is optimized, and the bond lengths, dipole moments, vibration frequencies and other physical properties parameters are obtained. On the basis of adopting the energy of high precision coupled cluster CCSD (T) method and the same basis set to scan single point energies, the potential energy curves of different external fields are given. The results show that the physical properties parameters and potential energy values will change with the changes of external electric fields, especially, of the reverse direction electric field. In order to get the critical dissociation electric parameter, the dipole approximation is adopted to construct potential model, then the model is put to fit the corresponding potential energy curve of external electric field. It is found that the fitted critical dissociation electric parameter is reasonably consistent with the numerical calculation; i.e., the relative errors are also less than 7%. So the model constructed is reliable and accurate. These will provide important theoretical and experimental reference for the studies of molecular spectroscopy, dynamics and molecular cooling with Stark effect.
