MOLPRO

17 THE DENSITY FUNCTIONAL PROGRAM 111
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
17.3.1 Target quadrature accuracy (GRIDTHRESH)
GRIDTHRESH,acc,accr,acca
Specify the target accuracy of integration. Radial and angular grids are generated adaptively,
with the aim of integrating the Slater-Dirac functional to the specified accuracy. acc is an overall
target accuracy, and is the one that should normally be used; radial and angular grid target
accuracies are generated algorithmically from it. However, they can be adjusted individually by
specifying accr and acca respectively.
17.3.2 Radial integration grid (RADIAL)
RADIAL,method,m r ,scale,n 0 ,n 1 ,n 2 ,n 3
Specify the details of the radial quadrature scheme. Four different radial schemes are available,
specified by method = EM, BECKE, AHLRICHS or LOG, with the latter being the default.
EM is the Euler-Maclaurin scheme defined by C. W. Murray, N. C. Handy and G. J. Laming,
Mol. Phys. 78 (1993) 997. m r , for which the default value is 2, is defined in equation (6) of the
above as
x m r
r = α
(1 − x) m r
(1)
whilst scale (default value 1) multiplied by the Bragg-Slater radius of the atom gives the scaling
parameter α.