In addition to the full ic1ion module, there is a derived module, icf1ion, in which only the lowest energy term of constant and is considered. Thus, the Coulomb interaction (see next section) is supposed to have such high energy that the low temperature physical properties may be accounted for just by the spin-orbit, crystal field, and exchange interactions. As a smaller energy matrix is required in this module, calculations will be faster. In the cases of a single outer shell electron or hole (e.g. Ce or Yb), the two modules are identical. icf1ion accepts the same inputs as ic1ion, except that the Slater integrals are ignored.
Currently (version 4.0), the beyond dipole part of mcdisp is not yet implemented, as are the calculations of the spin and orbital moment densities. All other packages may use icf1ion.