By default in ADF a point charge model is used for the nuclear charge distribution. In ADF2009.01 a spherical Gaussian nuclear charge distribution model has been implemented in ADF, see Ref. [270]. Nuclear finite size effects can have large effects on hyperfine interactions (ESR A-tensor, NMR spin-spin coupling) if heavy atoms like, for example, Mercury (Hg), are involved. In Ref. [270] it was written that the isotropic J-couplings (parameters in NMR spin-spin coupling) are typically reduced in magnitude by about 10 to 15 % for couplings between one of the heaviest NMR nuclei and a light atomic ligand, and even more so for couplings between two heavy atoms. This Ref. [270] gives more details on the parameters used in the Gaussian nuclear charge distribution model. Note that one needs basis sets with very tight functions to see any effect of using a finite size of the nucleus instead of a point nucleus. Such basis sets can be found for some elements in $ADFRESOURCES/ZORA/jcpl, which are basis sets especially designed for NMR spin-spin coupling calculations.
A Gaussian nuclear charge distribution will be used if one uses the NUCLEARMODEL key with:
NUCLEARMODEL gaussian
NUCLEARMODEL nuclearmodel
The argument nuclearmodel of the key NUCLEARMODEL can be 'pointcharge' (default) or 'gaussian'. It should be included in the Create run of an atomic calculation and in the molecular calculation. If the BASIS key is used it will be automatically added in the Create run of the atoms. If this key is absent a point charge nuclear model is used.
In the ADF output parameters will be shown for the Gaussian nuclear charge distribution if one includes in the input for ADF:
PRINT Nuclei
