Electronic and magnetic structure of bulk cobalt: the alpha, beta, and epsilon-phases from density functional theory calculations.

The geometric, electronic and magnetic properties of the three metallic cobalt phases: hcp(alpha), fcc(beta), and epsilon(epsilon) have been theoretically studied using periodic density functional calculations with generalized gradient approximation (GGA) and plane wave basis set. These results have been compared with those obtained with GGA+U approach which have shown a noticeable improvement with regard to experimental data. For instance, the cohesive energy values predicted by GGA are overestimated by approximately 25%, whereas GGA+U underestimate them by 14%-17%. On the other hand, magnetic moment values are underestimated in GGA while are overestimated for GGA+U approach by almost the same amount. Besides, the introduction of U parameter gives rise to an electronic redistribution in the d-band structure, which leads to variations in the magnetic properties. Moreover, a higher attention has been paid in the study of the electronic and magnetic properties of the epsilon-phase that has not described previously. These studies show that this phase possesses special properties that could lead to an unusual behavior in magnetic or catalytic applications.