Gradient-Corrected Density Functional Calculation of Elastic Constants of Fe, Co and Ni in bcc, fcc and hcp Structures

Systematic ab initio calculations of lattice constants, elastic constants and magnetic moments of Fe, Co and Ni in bcc, fcc and hcp structures have been carried out, in part to understand the phase stability and magnetic properties of artificial Fe, Co and Ni structures. The calculations are based on the local spin-density functional theory with generalized gradient corrections (GGA) which are found to describe the properties of these materials rather well. In particular, the calculated lattice constants and bulk modulus of the observed structures are in good agreement with experiments. Also, the theoretical elastic constants agree with the measurements within the numerical uncertainties. Interestingly, several energetically metastable structures are found to be elastically unstable. It is predicted that magnetism has a pronounced influence on both the size and sign of some elastic constants, and hence on the structural stabilities. For example, while both nonmagnetic Fe fcc and hcp structures are metastable phases, ferromagnetic Fe fcc and hcp structures are not. These results would help to gain insight into the formation of certain artificial thin films and superlattices.