La interactions with C and N in bcc Fe from first principles

Behaviors of a single FA (foreign atom, i.e., C, N or La) in bcc Fe and interactions of LaC/N are investigated by first-principles calculations based on the density functional theory. Results indicate that La atom prefers to occupy substitutional site and anti-bonding states build up between La and Fe atoms. Fe atoms around La are relaxed to move far away from La and the relaxed distances caused by La are greater than other alloying elements (Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo). A strong repulsive interaction builds up between La and C/N atoms. And the LaC repulsive interactions are greater than LaN at distance within a bcc lattice parameter, less than LaN beyond a lattice parameter. Morever, LaC/N interaction energies are markedly greater than other FSA (Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Nb and Mo)-FIA interaction energies. Density of states and Mulliken bond populations are also analyzed and indicate the formation of an interaction between La and C/N atoms, and the interaction decreases with increasing LaC/N distance. Furthermore, the introduction of La atom causes the increase of C/NFe bond populations, which is beneficial to the improvement of material’s strength.