Local Energies and Energy Fluctuations - Applied to the High Entropy Alloy CrFeCoNi

High entropy alloys show a variety of fascinating properties like high hardness, wear resistance, corrosion resistance, etc. They are random solid solutions of many components with rather high concentrations. We perform ab-initio calculations for the high entropy alloy CrFeCoNi, which equal concentration of 25% for each element. By the KKRnano program package, which is based on an order-N screened Korringa-Kohn-Rostoker Green's function method, we consider a face-centered cubic (FCC) supercell with 1372 randomly distributed elements, and in addition also smaller supercells with 500 and 256 atoms. It is found from our calculations that the local moments of the Cr atoms show a large environmental variation, ranging from -1.70 mu(B) to + 1.01 mu(B) with an average of about - 0.51 mu(B). We present a new method to calculate local energies of all atoms. This is based on the partitioning of the whole space into Voronoi cells and allows to calculate the energetic contribution of each atomic cell to the total energy of the supercell. The supercell calculations show very large variations of the local energies, analogous to the variations of the local moments. This shows that the random solid solution is not stable and has a tendency to form an L1(2)-structure with the Cr-atoms ordered at the corner of the cube and the elements Fe, Co, and Ni randomly distributed on the three other FCC sublattices. For this structure the variation of the local moments are much smaller.