On the integration accuracy in molecular density functional theory   calculations using Gaussian basis sets
  The sensitivity of computed DFT (Density Functional Theory) molecular properties (including energetics, geometries, vibrational frequencies, and infrared intensities) to the radial and angular numerical integration grid meshes, as well as to the partitioning scheme, is discussed for a number of molecules using the Gaussian 98 program system. Problems with typical production grid sizes are particularly acute for third-row transition metal systems, but may still result in qualitatively incorrect results for a molecule as simple as CCH. Practical recommendations are made with respect to grid choices for the energy(+gradient) steps, as well as for the solution of the CPKS (Coupled Perturbed Kohn-Sham) equations. 
Jan M.L. Martin, Charles W. Bauschlicher, Jr., and Alessandra Ricca