Electronic Structures of Metal Carbides TiC and UC: Similarity and Dissimilarity

Abstract To elucidate the nature of chemical bonding in metal carbides with the NaCl structure, the valence electronic states for TiC and UC have been calculated using the discrete-variational (DV) Xα method. Since relativistic effects on chemical bonding of compounds containing uranium atom become significant, the relativistic Hamiltonian, i.e., the DV-Dirac-Slater method, was used for UC. The results obtained using a neutral cluster model of C-M6-C12-C6 with Oh symmetry are compared with each other. The present calculations for the UC and TiC reproduce fairly well the peak position of the experimental valence X-ray photoemission spectrum indicating that the cluster model is appropriate to treat with the bulk properties of the metal carbides. The Mulliken population analysis demonstrated that the ionicity of UC is greater than that of TiC while the covalency of UC is weaker than that of TiC. This discrepancy between the bond nature of the two compounds is discussed in connection with the similarity and dissimilarity of their physical properties.