The inversion potential for NH₃ using a DFT approach

Using a density functional theory approach, we generate a potential energy surface (PES) and, by a least-squares method, we obtain a polynomial function which represents the unidimensional potential along the inversion coordinate, with a very high precision. The inversion spectrum of NH₃ is then determined by solving the Schrödinger equation for this potential, using a better approximated reduced mass which is a function of the inversion coordinate. The calculated inversion frequencies obtained through this method are compared against those generated by Hartree-Fock theory and also with the experimental values. We find that our theoretical results are by far the most accurate.