GHOSTS

The subkey GHOSTS is a block type subkey. The format is:

Ghosts
   xx1 yy1 zz1
   xx2 yy2 zz2
   ......
SubEnd

With this key, the user can specify ANY point(s) within the molecule at which the shielding is to be calculated (whatever the physical meaning of this shielding is). One can think of those points as neutrons within the molecule. There is a publication by P. Schleyer et al. using a similar feature

(J. Am. Chem. Soc. 118, 6317, 1996). They call it NICS, Nucleus-Independent Chemical Shift. Note that the NICS value is minus 1 times the isotropic part of the shielding tensor that is calculated at these points.

xx1 yy1 zz1

real numbers that specify the Cartesian coordinates of 'ghost' 1, etc.

The coordinates have to be specified in the same units as any other input (ADF subkey Units). That is, you use Angstrom for the ghosts if you did so for the atomic coordinates, or bohr otherwise. The same set of coordinates has to be specified as 'point charges with charge zero' using the key EFIELD. This is necessary in order to allow the appropriate distribution of integration points around the ghosts.

E.g., if you want to have two 'ghosts' with the coordinates xx1 yy1 zz1 and xx2 yy2 zz2 then you must also have in the input the key EFIELD as follows

EFIELD
 xx1 yy1 zz1   0.0
 xx2 yy2 zz2   0.0
END

(the last number is the charge at these coordinates - zero).

Eventually, this step should be programmed internally but for now the procedure outlined above works. No check is done to verify whether those 'point charges' are taken care of or not, but their omission leads to unpredictable results.

Only Cartesian coordinates are possible for ghosts, even if the atoms were originally specified using internal coordinates. This shouldn't be a problem, though (e.g., one could start an ADF run of the molecule of interest, and get very soon the Cartesian coordinates of the atoms in the output. This run would then be aborted, and restarted with the ghosts specified as desired.) The ghosts are numbered in the output as NNUC+1, NNUC+2 ... where NNUC is the total number of nuclei in this molecule. Default: no ghosts.