  Using first-principles density functional theory in the implementation of the
exact muffin-tin orbitals method and the coherent potential approximation, we
studied the surface energy and the surface stress of the thermodynamically most
stable surface facet (100) of the homogeneous disordered body-centred cubic
iron-chromium system in the concentration interval up to 20 at.% Cr. For the
low-index surface facets of Fe and Cr, the surface energy of Cr is slightly
larger than the one of Fe, while the surface stress of Cr is considerably
smaller than the one of Fe. We find that Cr addition to Fe generally increases
the surface energy of the Fe-Cr alloy, however, an increase of the bulk amount
of Cr also increases the surface stress. As a result of this unexpected trend,
the (100) surface of Fe-Cr becomes more stable against reconstruction with
increasing Cr concentration. We show that the observed trends are of magnetic
origin. In addition to the homogeneous alloy case, we also investigated the
impact of surface segregation on both surface parameters.
