The effect of grid quality and weight derivatives in density functional calculations

Full density functional geometry optimizations on hydrogen peroxide and heptane/dimethyl pentane using six different numerical grids are presented. The grids vary in quality and gradients are calculated (1) assuming a fixed grid and no weight derivatives, and (2) with full allowance for a ‘‘moving’’ atom‐centered grid and inclusion of the weight derivatives. 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 results for grids which are of insufficient quality to guarantee reliable values in any case.