CAN (SEMI)LOCAL DENSITY-FUNCTIONAL THEORY ACCOUNT FOR THE LONDON DISPERSION FORCES

The reproduction of the interatomic potential in He-2, Ne-2, and Ar-2 by Kohn-Sham theory is investigated using a density functional program which can perform counterpoise corrections for both basis sets and numerical integration. None of the functionals considered accounts successfully for the dispersion interaction. The Becke exchange and the Becke-Lee-Yang-Parr (B-LYP) exchange-correlation functionals yield a purely repulsive potential after counterpoise correction. The Dirac-Slater (D-S) functional gives minima which are too deep, at internuclear distances which are too short, particularly for He-2 and Ne-2. The experimental repulsive potential is reproduced best by D-S calculations while the B-LYP results are close to the SCF ones.