An ab initio and DFT study of (N2)2 dimers

The structure of van der Waals dimers (N-2)(2) is studied using ab initio and density functional calculations. The potential energy surfaces corrected a priori for basis set superposition errors are necessary for determining both the geometries and the vibrational frequencies. With both ab initio MP2, MP4 and DFT PW91-PW91 levels of theory, the T-shaped and canted conformations appear to be the most stable, within 1-5 cm(-1) of each other. The DFT PW91-PW91 dissociation energy is 67 cm(-1) and an upper limit to the barrier to internal motion is 30 cm(-1), both in excellent agreement with the values deduced from IR measurements. (C) 1999 Elsevier Science B.V. All rights reserved.