Fully relativistic first-principles electronic structure calculations of both the average structure and a supercell approximation of silver-free incommensurately modulated calaverite (AuTe2) are presented. The differences between the results of both calculations are relatively small for the occupation numbers and the density of states, but quite dramatic for the shape of the Fermi surface. From the occupation numbers it is concluded that a previously proposed idea for explaining the modulation, based on mixed valencies for the gold atoms, is probably not applicable. The calculated Fermi surface of the average structure shows that the modulation cannot be understood in terms of Fermi-surface nesting either. The density of states in the supercell approximation compares very favourably with recently obtained X-ray photoelectron spectroscopy data. A rigid-potential calculation shows that the integral of the one-electron valence energies for the supercell is substantially more negative than the corresponding energy for the average structure, while the electrostatic energy difference has the opposite sign but is much smaller. This provides a qualitative indication of the electronic instability of the average structure with respect to the modulation of the supercell. Finally the authors conclude that Te s-like states a (Te p-Au d)-like complex dominate the energetics of the modulation.

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AbstraQ. We model the local electronicstructure around acore-ionizedsite inasimple metal self-consistently using an embedding technique. We consider the local densities of stales of Na, Mg and AI and calculate from first principles KLV Auger profiles. The success of this approach is assessed by comparison with experiment and with approximations which may be used to simplify the calculation. The agreement with experiment is on the whole good although some discrepancy arises for the case of W . , V lineshapes.

We report ab initio calculations of quantum-well states in Cu/Co͑001͒ and Co/Cu͑001͒ overlayers and in Co/Cu/Co͑001͒ sandwiches. Overlayer states are found which coincide well with those previously identified in photoemission and inverse photoemission experiments. In Cu/Co and at energies overlapping with the substrate continuum, minority spin resonances are clearly identifiable. However, in the majority spin channel coupling to the substrate is strong enough to effectively destroy quantum-well features. In Co/Cu/Co͑001͒ sandwiches discrete states are found at similar energies to those in overlayers of corresponding Cu thicknesses, but well defined resonance states are absent in both spin channels. There is no longer a strongly size-dependent electronic structure at the Fermi energy. We conclude care must be taken in extrapolating from the electronic structure of overlayer systems to that of other modulated structures.

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