GEOMETRIC STRUCTURE OF AR-CENTER-DOT-NO- REVISITED - A FAILURE OF DENSITY-FUNCTIONAL THEORY( )

High level ab initio calculations are performed on the Ar . NO+ comple x to ascertain its geometric structure. The calculations show that the complex is bent, with an Ar-N-O angle of similar to 105 degrees, i.e. the argon atom is on the nitrogen side of the complex cation. Calcula tions are performed with the cc-pVDZ and cc-pVTZ basis sets at the MP2 , MP4(SDQ), QCISD, CISD, CCSD(T), and QCISD(T) levels of theory; in ad dition the hybrid density functionals BLYP, B3LYP, and BPW91 are used. Harmonic vibrational frequencies are also calculated for all except t he two highest levels of theory, but it is recognized that the surface is anharmonic and these are not good estimates of the vibrational sep arations; however, by comparison with the ab initio results, they demo nstrate that these density functional methods are not trustworthy for this complex. (C) 1996 American Institute of Physics.