Note that the 1-norm is used in this expression since it then becomes identical to the localization criterion of the direct orbital selection. Therefore, the orbital maps are expected to be similar to the previously used orbital set maps from the direct orbital selection except for those orbitals that were assigned to the set of "unmappable" orbitals. Hence, the equation to obtain orbital maps displays a linear assignment problem that is solved separately for core and valence orbitals using the Hungarian method as for Eq. (8). A resulting orbital map is illustrated in Fig. .