First-principles calculations on crystal structure and physical properties of rhenium dicarbide

Structural stability, elastic behavior, hardness, and chemical bonding of ideal stoichiometric rhenium dicarbide (ReC2) in the ReB2, ReSi2, Hex-I, Hex-II, and Tet-I structures have been systematically studied using first-principles calculations. The results suggest that all these structures are mechanically stable and ultra-incompressible characterized by large bulk moduli. Formation enthalpy calculations demonstrated that they are metastable under ambient conditions, and the relative stability of the examined candidates decreases in the following sequence: Hex-I > Hex-II > ReB2 > Tet-I > ReSi2. The hardness calculations showed that these structures are all hard materials, among which the Hex-I exhibits the largest Vickers hardness of 32.2 GPa, exceeding the hardness of alpha-SiO2 (30.6 GPa) and beta-Si3N4 (30.3 GPa). Density of states and electronic localization function analysis revealed that the strong C-C and C-Re covalent bonds are major driving forces for their high bulk and shear moduli as well as small Poisson's ratio. (C) 2012 Elsevier Ltd. All rights reserved.