FERMI SURFACES AND ELECTRONIC TOPOLOGICAL TRANSITIONS IN METALLIC RANDOM ALLOYS .2. AGCPD1-C

We have calculated the Fermi surfaces of AgcPd1-c vs Ag atomic concentration, within the fully relativistic Korringa-Kohn-Rostoker-coherent-potential-approximation framework. The Fermi surfaces of these alloys change, on varying the concentration, from the Pd- to the Ag-like topology. This implies that a number of electronic topological transitions (ETT's) occur on changing the e/a ratio, as a consequence of the fact that the Fermi level moves away from the d states towards the sp states. It is well known that such changes in connectivity of the Fermi surfaces affect transport coefficients; however, as we have shown in Paper I, equilibrium properties such as equilibrium volume, specific heat, enthalpy of mixing, etc., also display anomalies at the same concentrations where such topological changes occur. In particular we have found 5 ETT's in correspondence to the deviations from Vegard's law of the lattice parameter shown in Paper I. Another unexpected result of this study is that, in the range of atomic concentration beteen 0.55 and 0.69, this alloy Fermi surface is simply connected, although nonspherical, as for a simple metal. Moreover, we show that a fully relativistic study is necessary for AgPd Fermi surfaces, because the spin-orbit interaction is responsible for the fact that the two hole pockets at X close at different concentrations.