A MODEL POTENTIAL FOR THE INTERNAL-ROTATION OF NITROSYL HYPERFLUORITE - A COMPARATIVE-ANALYSIS OF DIFFERENT THEORETICAL METHODS

We present a comparative analysis of the internal rotation energy curves of nitrosyl hyperfluorite (FO-NO). Two model potentials, derived from a Fourier series expansion, have been used to rationalize the trans half arrow right over half arrow left cis isomerization process for different theoretical methods going from traditional molecular orbital calculations to density functional theory. It is shown that Hartree-Fock (HF) and post Hartree-Fock (pHF) calculations, using a sufficiently large basis set, lead to results that are qualitatively similar. However, local density functional (LDF) calculations produce results that are not compatible. The resulting barrier heights vary from 2.36 (LDF) to 12.76 kcal/mol (MP4SDTQ/6-31G*) passing through a value of 8.33 kcal/mol from a HF/6-31 G calculation. It is concluded that the LDF results, within the approximations used in that calculation, appear to be anomalous when compared to the HF and pHF results.