Rhombohedral graphite: Comparative study of the electronic properties

Studies on rhombohedral graphite are often performed by exploiting the hexagonal P3 symmetry of its conventional cell. The primitive cell of that graphite, however, is rhombohedral, with an R3¯m symmetry. That difference in symmetry introduces variations in the electronic properties that we want to ascertain in this work. We used the CRYSTAL computational code to calculate the density of states DOS, electronic structure, electrostatic potential, and electric charge maps, with DFT-LDA, GGA, Hybrid, and Hartree-Fock Hamiltonians, as well as LDA-Perdew-Zunner and LDA-Vosko-Wilk-Nusair exchange-correlation potential pairs, the wave function being expanded in STO-6G and 6-31G basis sets. The hexagonal to rhombohedral deformation of the First Brillouin Zone produces modifications in the band structure, enhancing the theoretical semiconductor character of rhombohedral graphite when a rhombohedral unit cell is used. When a conventional hexagonal cell and Hartree-Fock Hamiltonians are used, the semimetal character of rhombohedral graphite is related to the inadequate self electron correlation and to the unit cell considered, the gap bands being more accentuated in the rhombohedral unit cell. Contour maps differences for different electronic properties under the different calculation conditions confirm the lamellar character of this graphite and the influence of the calculation conditions on the electronic properties.