First-principles study on the structural stability, electronic and magnetic properties of Fe2C

First-principle calculations are carried out to investigate the structural, elastic and electronic properties of Fe2C. We use the plane-wave-based-pseudo-potential method, in which both the local-density approximation (LDA) and the generalized gradient approximation (GGA) implanted in the CASTP code are employed. The internal positions of atoms in the unit cell are optimized and the ground state properties such as lattice parameter, elastic constants, bulk modulus and the final enthalpy of eta-Fe2C and epsilon-Fe2C are calculated. The calculated values compare favorably with the available experimental data. From the calculated results, we confirm that the mechanical and energetic stability of eta-Fe2C are prior to epsilon-Fe2C at ambient conditions. The density of state (DOS) reveals that both eta-Fe2C and epsilon-Fe2C are strong metallic carbides. The electronic structure explains that the bonds of Fe2C are of the unusual mixtures of metallic, covalent, and ionic. It is found that the epsilon-Fe2C has no magnetic character from the spin-polarized site-projected densities of states. The eta-Fe2C has magnetic character with atom-averaged magnetic moment of 1.09 mu(B), which is little smaller than that within the Slater-Pauling-Friedel (SPF) model. (C) 2007 Elsevier B.V. All rights reserved.