For example, calculations on lanthanides complexes can only be accurate if the 4f electrons are part of the valence space. Moreover, the small extent of these 4f orbitals around the nucleous calls for ultrasoft pseudopotentials in order to reduce the computational cost. We have thus constructed such a (Vanderbilt's) pseudopotential for the gadolinium atom using the PBE exchange-correlation density functional.
As the official version of the CPMD program does not allow Vanderbilt's pseudopotentials with electrons in the f channel (because the Clebsch-Gordan coefficients are tabulated up to the d angular momentum), we use our own development version.
R. Pollet, C. Clavaguéra, and J.-P. Dognon. Ultrasoft pseudopotentials for lanthanide solvation complexes: Core or valence character of the 4f electrons. J. Chem. Phys. 2006, 124, 164103.