Linear augmented-Slater-type-orbital method for electronic-structure calculations. V. Spin-orbit splitting in ${\mathrm{Cu}}_3$Au

We have used local-density-functional theory to calculate the energy bands, heat of formation, and core-level shift in the classic ordering alloy ${\mathrm{Cu}}_3$Au. Contrary to expectations we find that the d bands are largely nonoverlapping with the gold region extending from -4 to -7 eV relative to the Fermi level. The copper d levels are concentrated in the range -1 to -4 eV. Addition of spin-orbit splitting strongly mixes the gold states, producing features which are predominantly j=(5/2 and j=(3/2 with the (5/2 level split weakly by the residual crystal-field effects. This agrees with the interpretation of photoemission data by Eberhardt et al. The total energy yields a heat of formation of -0.048 eV/atom compared with the experimental value of -0.07 eV/atom. The Au 4f core-level position was calculated using a total-energy approach. The fully relaxed shift was found to be 0.3 eV (to larger binding energy) compared with the experimental value of 0.48 eV. The absolute value of the core-level binding energy was calculated to be 84.1 eV, compared to 84.40 eV experimentally.