By setting different electric fields and adopting density functional B3P86 and high precision coupled cluster CCSD (T) method, combining with relevant agreement Dunning five heavy cc-PV5Z, the geometric structure of PH molecule is optimized and the single point energies are scanned. The bond lengths, dipole moments, vibration frequencies, infrared spectrum and potential energy curves are obtained. The results show that the physical properties parameters and the potential energy values will change with the change of external electric field, especially at reverse direction electric field. In order to analyze the external field effect and 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 2%. So the constructed model is reliable and accurate for analyzing the external field effect. These will provide important theoretical and experimental reference for the studies of molecular spectroscopy, dynamics and molecular cooling with Stark effect.
