  The formation energy of the interface between face-centered cubic (fcc) and
hexagonal close packed (hcp) structures is a key parameter in determining the
stacking fault energy (SFE) of fcc metals and alloys using thermodynamic
calculations. Often the contribution of the planar fault energy to the SFE has
the same order of magnitude as the bulk part, and thus the lack of a precise
information about it can become the limiting factor in thermodynamic
predictions. Here, we differentiate between the actual interfacial energy for
the coherent fcc(111)/hcp(0001) interface and the "pseudo-interfacial energy"
that enters the thermodynamic expression for the SFE. Using first-principles
calculations, we determine the coherent and pseudo- interfacial energies for
six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and for three paramagnetic
Fe-Cr-Ni alloys. Our results show that the two interfacial energies
significantly differ from each other. We observe a strong chemistry dependence
of both interfacial energies. The calculated pseudo-interfacial energies for
the Fe-Cr-Ni steels agree well with the available literature data.
