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The relativistic KKR (Korringa–Kohn–Rostoker) Green's function method of band-structure calculation supplies an extremely flexible basis for calculating magnetic linear response functions of solids. An important feature of this approach is that it accounts properly for the influence of all relativistic effects. A brief introduction to this formalism is presented, together with some recent extensions to it. In particular, the inclusion of the orbital magnetization density induced by an external magnetic field allows a direct comparison with experiment for many different properties. This is demonstrated for the induced magnetic form factor, the magnetic susceptibility and the Knight shift of transition metals. A further appealing feature of the KKR formalism is that it is applicable in principle to any complex system. This property is exemplified by applications for the disordered alloy systems AgxPd1−x and AgxPt1−x that are treated with the help of the coherent potential approximation alloy theory.

In this paper three different ways to calculate the temperature dependent susceptibility of the enhanced paramagnets Pd and Pt are presented and compared. Special attention is paid to the relative importance of one-particle and many-particle excitations. One of these methods has never been applied before to real itinerant systems. It is based upon Onsager's reaction field model, which seems to be a feasible and rigorous way to go beyond the mean field approximation, and it allows one to make quantitative statements. The backbone of this theory is the calculation of a temperature dependent Hubbard U due to thermal many-body excitations. In contrast to an earlier calculation we found a significant temperature dependence of U for Pd. The theoretical results are in fairly reasonable agreement with the experimental findings for both Pd and Pt.