title: CuNO2 and Cu(+)NO2 Revisited:  A Comparative ab Initio and DFT Study.
abstract: We have reinvestigated CuNO2 and Cu(+)NO2 at ab initio as well as at pure and hybrid DFT levels of approximation employing large ANO basis sets. The systems were fully optimized using the CCSD(T), QCISD(T), BPW91, PBE, PBE0, and B3LYP methods. Several stationary points (minima and transition structures) were found on the related potential energy surfaces (PES). The C2v bidentate η(2)-O,O isomer is calculated to be the most stable species on the CuNO2 PES, followed by two monodentate isomers [Formula: see text] the Cs η(1)-O and C2v η(1)-N species which are higher in energy by 12 and 14 kcal/mol, respectively, at CCSD(T)/Basis-II (where Basis-II is 21s15p10d6f4g/8s7p5d3f2g for Cu; 14s9p4d3f/5s4p3d2f for O and N). On the Cu(+)NO2 PES, the Cs monodentate η(1)-O trans (0 kcal/mol) and cis (+3 kcal/mol at CCSD(T)/Basis-II) isomers are found, followed by the C2v monodentate η(1)-N isomer (+14 kcal/mol at CCSD/Basis-II). In contrast to the pure DFT, the hybrid DFT methods perform reasonably well for predicting the relative stabilities (except for η(1)-N of CuNO2) and structures; however, their predictions of the bond dissociation energies are less reliable (for CuNO2 the difference is as much as 10 kcal/mol compared to the CCSD(T) values). The performance of the QCISD(T) method was analyzed, and, furthermore, the issue of symmetry breaking was investigated.
authors.affiliation: J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 18223 Prague, Czech Republic.
authors.forename: Stepan
authors.initials: S
authors.lastname: Sklenak
authors.affiliation: J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 18223 Prague, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Hrušák