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In all relativistic calculations - scalar as well as spin-orbit - the relativistic atomic core densities and the relativistic atomic potentials must be made available to ADF on a file specified with the key COREPOTENTIALS. Starting from the ADF2006.01 release this is necessary only in the 'create' run of the atoms. In the molecular calculation this key is not required anymore. If supplied then the file must contain data for all atom types in the molecule, even for those atoms where relativistic aspects are expected to be negligible or that may not have a frozen core at all (such as Hydrogen). Excepted are any Ghost atoms (for instance for a BSSE calculation): these can not have any core potentials. This is tested by the program, internally, by looking at the nuclear charge and at the number of electrons belonging to an atom: if both numbers are zero, no (relativistic or other) core potential is allowed. Also the potential used in the ZORA kinetic energy operator in the SAPA (sum of neutral atomic potential approximation) method should be present on this file (which will be the case if the program DIRAC is used to generate this file).
Relativistic potentials can and should be generated with the auxiliary program dirac, see the Utilities document, and the examples.
As of ADF2003, the recommended way to generate atomic fragments and relativistic potentials is by using the BASIS keyword.
