Stacking two or more single graphene layers on top of one another may, however, change most of the electronic properties of graphene. In the solid state, Bernal graphite is the most common form, where the graphene layers are stacked in the ABAB fashion, such that centers of 6-fold rings of one layer are situated on top of carbon atoms in the second layer, forming the so-called staggered structure. Bernal graphite requires four carbon atoms in the unit cell, which results in four bands at the K point of the Brillouin zone close to the Fermi level, however, they are now parabolic rather than linear, and, thus, give rise to massive electrons in a zero-gap semiconductor (see Figure , see also Refs. [50,51]). On the other hand, an almost linear (more accurately, a parabolic dispersion with very large curvature) and very small effective mass can be seen at the H point of the Brillouin zone, with the Fermi level slightly below the top of the valence band and a band gap of about 5 meV, thus, a few orders of magnitudes larger than in graphene. ), and (c) eclipsed graphite (AAAA stacking, hypothetical). Single layer of graphene, which exhibits Dirac points (linear dispersion relation) at K points and a band gap of about 1 eV, changes its electronic properties when stacked differently into 3D structures: ABAB graphite has quadratic and nearly linear dispersion relations at the K and H points, respectively, and band gap at H of 5 meV; AAAA graphite has two Dirac points (at K and H points) above and below Fermi level (blue dashed horizontal lines). Simulations at the DFT/PBE-D3(BJ) level of theory with TZP basis set and spin-orbit coupling as implemented in AMS/BAND software. Pictures of structures made with VESTA. In a hypothetical structure of eclipsed graphite (AAAA stacking of layers, Figure ), an intriguing electronic structure emerges. Two atoms per unit cell and one layer are necessary to represent the smallest possible 3D structure. There are two nearly linear bands at the K point close to the Fermi level, similar to graphene. However, the two Dirac points without band gaps at K and H points are above and below the Fermi level, respectively. Thus, the  and  * bands are not symmetric with respect to the Fermi level. This demonstrates that the proximity effect depends both on the distance between the layers and on the mutual shift of the crystal planes.