22.3 Numerical integration grid control (GRID)

Density functionals are evaluated through numerical quadrature on a grid in three-dimensional space. Although the sensible defaults will usually suffice, the parameters that define the grid can be specified by using the GRID top-level command, which should be presented before the the DFT or KS commands that will use the grid. Alternatively, GRID and its subcommands can be presented as directives within the KS program.

GRID,orb.file,status

The integration grid is stored on record orb.file (default 1800.2). The information on disk consists of two parts: the parameters necessary to define the grid, and a cache of the evaluated grid points and weights. The latter is flagged as `dirty' whenever any parameters are changed, and whenever the geometry changes; if the cache is dirty, then when an attempt is made to use the grid, it will be recalculated, otherwise the cached values are used.

If status is OLD, an attempt to restore the grid from a previous calculation is performed; effectively, the old grid provides a template of parameters which can be adjusted using the parameter commands described below. If status is NEW, the grid is always created with default parameters. If status is UNKNOWN (the default), a new grid is created either if record orb.file does not exist; otherwise the old grid is used.

The GRID command may be followed by a number of parameter-modifying subcommands. The currently implemented default parameters are equivalent to the following input commands.

GRIDTHRESH,1e-5,0,0
RADIAL,LOG,3,1.0,20,25,25,30
ANGULAR,LEBEDEV,0.0,0.0
LMIN,3,5,5,7
LMAX,53,53,53,53
VORONOI,10
GRIDSAVE
GRIDSYM