Physical models of sodium crystal, graphite crystal, a molecule of carbon nanotube in armchair type and their Wigner-seitz cells are built. Computer programes are written to calculate the energy levels of their ions, atoms, crystals and molecule. Their effective atomic numbers are calculated to construct their potentials. For crystals muffin-tin potential is used as well as boundary condition of Wigner-Seitz. Bloch theorem and one-dimensional model are used as well for sodium crystal. The result is that sodium is a conductor. The result for graphite is that it is a conductor in the plane of atoms. For carbon nanotube in armchair type, the energy level of the outer most electron is -40.26 eV. This energy is higher than the top of potential barrier. So it is in conduction band and carbon nanotube of this type is a conductor.