First-principles study of structural, elastic and electronic properties of thorium dicarbide (ThC2) polymorphs

The comparative study of the structural, elastic, cohesive and electronic properties of three polymorphs (α-monoclinic, β-tetragonal and γ-cubic) of thorium dicarbide ThC₂ is performed within the density-functional theory. The optimized atomic coordinates, lattice parameters, theoretical density (ρ), bulk moduli (B), compressibility (β), as well as electronic densities of states, electronic heat capacity (γ) and molar Pauli paramagnetic susceptibility (χ) for all ThC₂ polymorphs are obtained and analyzed in comparison with available experimental data. The peculiarities of inter-atomic bonding for thorium dicarbide are discussed. Besides, we have evaluated the formation energies (E_f) of ThC₂ polymorphs for different possible preparation routes (namely for the reactions with the participation of simple substances (metallic Th and graphite) or thorium monocarbide ThC and graphite). The results show that the synthesis of the ThC₂ polymorphs from simple substances is more favorable - in comparison with the reactions with participation of Th monocarbide.