Each block of points (see above) covers (more or less) a certain region in space and can hence be assigned a distance value with respect to a particular atom. These distances are used to control whether or not to evaluate funtions centered on that atom in that particular block of points.
TAILS {bas=tailbas} {fit=tailfit}
tailbas, tailfit
Accuracy levels, similar to the integration parameter: a higher value implies higher precision: in this case, basisfunctions and fitfunctions respectively are assumed zero in blocks of points that are at a sufficiently large distance from the atom at which the function is centered. Sufficiently large is defined by comparing the integral of the (radial part of the) function beyond that distance with the total integral. By default tailbas and tailfit both depend on the numerical integration parameter
Note: in contrast with some of the older versions, supplying only the keyword without parameters does not switch off the use of function cutoffs. To effectively switch off the distance effects in gradients evaluation one should specify large values for the BAS and FIT parameters. The value of 100 should be more than enough, thus, for example:
TAILS bas=100 fit=100
This key TAILS is currently obsolescent because of the introduction of the LINEARSCALING keyword and may be removed in future versions. At the moment it is still of use in geometry optimizations. For controlling the use of distance effects in normal SCF calculations, and for calculations with the RESPONSE or EXCITATIONS keywords, please check the LINEARSCALING keyword.
