The full-charge-density screened Korringa-Kohn-Rostoker method is described and applied to calculate bulk and surface energies of transition metals. It is demonstrated that due to a truncated angular momentum expansion of the shape functions, the otherwise ultimate freedom of adding a constant to the potential in all space leads, in particular close to the cell boundaries, to potentials of fairly different shapes. Thus a dependence on this constant potential shift emerges for the calculated bulk total energies, equilibrium volumes, and bulk moduli, as well as for the surface energies and the work functions. A reasonable choice for the constant shift seems to set the bulk potential at the muffin-tin radius to zero. By making this choice the calculations give results that are in very good agreement to those calculated by other full-charge-density or full-potential methods.

We study a model of charge transfer in alloys proposed by Bruno, Zingales, and Wang ͓Phys. Rev. Lett. 91, 166401 ͑2003͔͒ and show its connection with electron-electron correlations. We then investigate in detail the properties of Madelung and related matrices, the mechanism leading to the screening of the electrostatic interactions between atomic net charges in random alloys, and calculate the screened interactions. Furthermore, we derive an expression for the total energy and show that the fluctuation contributions to the local and Madelung energy mutually cancel. We then derive and discuss the probability distribution function of local charges and make a comparison with calculations for large supercells. Finally, we discuss the relation of the present approach to other theories aimed at the description of Coulomb effects in alloys.

We present ab initio calculations of the magnetic moments and magnetic anisotropy energies of small FeCo clusters of varying composition on top of a Cu͑100͒ substrate. Three different cluster layouts have been considered, namely, 2 ϫ 2, 3 ϫ 3, and crosslike pentamer clusters. The ratio of Co atoms with respect to the total number in a chosen cluster ͑"concentration"͒ was varied and all possible arrangements of the atomic species were taken into account. Calculations have been performed fully relativistic using the embeddedcluster technique in conjunction with the screened Korringa-Kohn-Rostoker method and the magnetocrystalline anisotropy energy ͑MAE͒ has been evaluated by means of the magnetic force theorem. A central result of the investigations is that the size of the magnetic moments of the individual Fe and Co atoms and their contributions to the anisotropy energy depend on the position they occupy in a particular cluster and on the type and the number of nearest neighbors. The MAE for the 2 ϫ 2 and 3 ϫ 3 clusters varies with respect to the concentration of Co atoms in the same manner as the corresponding monolayer case, whereas the pentamer clusters show a slightly different behavior. Furthermore, for the clusters with an easy axis along a direction in the surface plane, the MAE shows a significant angular dependence.

No abstract