An MP2 and density functional study of the oxides of nitrogen

Abstract

Equilibrium geometries, harmonic vibrational frequencies, atomization energies and heats of formation have been calculated for seven neutral oxides of nitrogen and compared with experimental values. We used standard Hartree-Fock and MP2 wavefunctions, together with local (SVWN), non-local (BP, BLYP) and hybrid HF-DFT (ACM or B3-PW91) density functionals. A good quality triple-zeta double polarization (TZ2P) gaussian basis was used throughout. Results using the ACM functional are by far the best, further emphasizing the quality and practical utility of hybrid density functionals for the prediction of molecular geometries and energetics. Local DFT predicts strongly exothermic heats of formation for all the nitrogen oxides except NO, in direct contradiction to experiment. Our ACM calculations predict that N 2O 5 has a C 2 equilibrium structure with the NO 2 groups twisted with respect to the central ONO plane by 31.6 °, in excellent agreement with gas phase electron diffraction data.