Simple approximations for the electronic structure of liquid metals

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Abstract
Simple approximations are derived from Roth's effective medium approximation (EMA) written in a locator-propagator representation. The EMA integral equation for the propagator is solved in an approximate way in order to make the calculation much less time-consuming. Two different approximations are proposed (AI and AII). The very simple AI is no more difficult than the non-self-consistent and quasi-crystalline approximation and much more accurate in the strong coupling case (transition metal). The AI satisfies exactly the non-overlap condition and provides the exact density-of-state second energy moment. It is superior in both respects to the self-consistent Gyorffy-Koringa-Mills approximation. The AII is no more difficult than the Ishida-Yonezawa theory but compares favourably with the EMA. It provides the first three energy moments and satisfies approximately the non-overlap condition. The reliability of the new approximations is studied numerically for a tight-binding and a muffin-tin model for liquid nickel. In both cases the AII density of states was found to compare well with the EMA one.