  This paper presents an approach for obtaining accurate interaction energies
at the DFT level for systems where dispersion interactions are important. This
approach combines Becke and Johnson's [J. Chem. Phys. 127, 154108 (2007)]
method for the evaluation of dispersion energy corrections and a Hirshfeld
method for partitioning of molecular polarizability tensors into atomic
contributions. Due to the availability of atomic polarizability tensors, the
method is extended to incorporate anisotropic contributions, which prove to be
important for complexes of lower symmetry. The method is validated for a set of
eighteen complexes, for which interaction energies were obtained with the
B3LYP, PBE and TPSS functionals combined with the aug-cc-pVTZ basis set and
compared with the values obtained at CCSD(T) level extrapolated to a complete
basis set limit. It is shown that very good quality interaction energies can be
obtained by the proposed method for each of the examined functionals, the
overall performance of the TPSS functional being the best, which with a slope
of 1.00 in the linear regression equation and a constant term of only 0.1
kcal/mol allows to obtain accurate interaction energies without any need of a
damping function for complexes close to their exact equilibrium geometry.
