The structure of van der Waals dimers (N2)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.