THE EFFECT OF GRID QUALITY AND WEIGHT DERIVATIVES IN DENSITY-FUNCTIONAL CALCULATIONS

Full density functional geometry optimizations on hydrogen peroxide an d heptane/dimethyl pentane using six different numerical grids are pre sented. The grids vary in quality and gradients are calculated (1) ass uming a fixed grid and no weight derivatives, and (2) with full allowa nce for a ''moving'' atom-centered grid and inclusion of the weight de rivatives. The results clearly demonstrate that accurate energies and geometries can be obtained with around 3500 points per atom for medium -sized systems (up to say 30 atoms) without the necessity of including the weight derivatives. The latter only begin to influence the result s for grids which are of insufficient quality to guarantee reliable va lues in any case.