The corresponding projections of the charge density onto the atoms and bonds are shown in Fig. with yellow volumes using multicell for the sake of extended views with the structure sketches and with a polyhedral view in left-hand-side and right-hand side representations, respectively. The trigonal character of C2-C2 pairs is also shown with a substantial charge density. But the most representative of the charge density difference between the two structures is observed in the change from a purely covalent system in tet-C 4 where the charge density is localized on each C atom with tetrahedra shape, to tet-C 6 where there is a continuous density charge from C1 (tetrahedral) to C2 (trigonal) allowing us to suggest a transition from the insulator (diamond) to a conductor. Indeed, the analysis of the electronic band structure in the subsection below will show such a result.