Tails and old gradients

The key TAILS is currently obsolescent because of the introduction of the LINEARSCALING keyword and may be removed in future versions. The key TAILS was used in older versions, ADF2004.01 and before, in the calculation of the gradients.

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 functions 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, basis functions and fit functions 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

Improved performance in geometry optimizations and frequency runs is achieved by a new implementation of the calculation of the gradients that now uses linear scaling techniques. This is now the default. One can still use the old implementation if one includes in the input:

OLDGRADIENTS

The key TAILS is not used in geometry optimizations anymore. 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.