[en] A review is given of recent progress in electronic structure determinations and in the development of new techniques for studies of electron-lattice coupling and magnetism. 24 refs., 6 figs

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[en] The electron--phonon spectral distribution function, α²(ω)F(ω), was calculated for niobium. The energy bands and wavefunctions were obtained from a self-consistent APW muffin-tin potential, and the matrix elements were evaluated using the so-called rigid ion approximation. Details of the calculation are presented and results compared with recent tunneling experiments, which confirm that the electron--phonon interaction is nearly three times larger for transverse phonons compared to the longitudinal phonons. It is shown that screening is of great significance and evidence is given which suggests that the same screening by d-electrons which causes the dips in the phonon dispersion curves of Nb is responsible for enhancing the electron phonon matrix elements and hence T/sub c/. An omission in the formulas of Gaspari and Gyorffy is pointed out

[en] Initial results for space charge-density distortions (CDD) associated with the q vector = (2/3,2/3,2/3) phonon in Nb and Mo are presented. Calculations were performed using the KKR method and muffin-tin approximation

[en] The temperature dependence of the [001]LO phonon branch in Zr is anomalous. At 6 K there is a dip in this branch at the zone center reminiscent of the anomalous dispersion observed in technetium--a high T/sub c/ superconductor. The anomaly can be related to electronic screening of the phonons. A simple model is proposed and the preliminary results of a frozen phonon calculation discussed

[en] Previous theoretical studies of the temperature dependence of the magnon dispersion curves of rare earth metals have usually considered only the renormalization due to spin-wave interactions and the effect of temperature variations of the magnetocrystalline anisotropy. An important consideration which has not been included in these studies is the possible temperature dependence of the exchange coupling between the localized spins. Taking into account only the shorter conduction electron mean free path and the resulting decrease in the 4f-4f coupling as T increases we obtain reasonable agreement with the measured magnon dispersion curves. Our results are consistent with recent measurements on Gd alloys which relate the temperature dependence of the magnetic ordering temperature to the conduction electron mean free path

[en] An initial self-consistent calculation of the ground state magnetic band structure of gadolinium is described. A linearized APW method was used which included all single particle relativistic effects except spin-orbit coupling. The spin polarized potential was obtained in the muffin-tin form using the local spin density approximation for exchange and correlation. The most striking and unorthodox aspect of the results is the position of the 4f spin-down ''bands'' which are required to float just on top of the Fermi level in order to obtain convergence. If the 4f states (l = 3 resonance) are removed from the occupied region of the conduction bands the magnetic moment is approximately .75 μ/sub B//atom; however, as the 4f spin-down states are allowed to find their own position they hybridize with the conduction bands at the Fermi level and the moment becomes smaller. Means of improving the calculation are discussed

[en] Materials with high superconducting transition temperatures frequently exhibit anomalous features in their phonon dispersion curves. The origin of these anomalies and their significance for superconductivity has been the subject of much debate. Two seemingly different models have been proposed to explain these anomalies in terms of the electron-phonon interaction. The first model focuses on real space charge-density distortions (CDD's), while the second emphasizes the states in reciprocal space near the Fermi energy. To test the assumptions in these models and to better understand the details of the electronic response to lattice vibrations in transition metals self-consistent frozen phonon calculations were performed for the (2/3, 2/3, 2/3) phonon in Nb and Mo. Initial results are reported for the CDD's associated with this phonon and discuss the differences between Nb and Mo

[en] In this paper a review of the electronic structure of rare earth materials is given, with emphasis on magnetic properties and recent X-ray and optical results. While the basic microscopic interactions between the 4f and conduction electrons are known and have been treated with phenomenological models for sometime, the complicated many body correlations among 4f electrons are still very difficult to evaluate from first principles (the same can be the about the correlations among the Cu-3d electrons in the high T_c superconductors). Nevertheless, it is important that first principles methods be further developed if theory, which has been greatly aided by modern computers, is to contribute to the analysis, design, and processing of new rare earth materials. Progress and remaining problems will be demonstrated by examples

[en] Many high T/sub c/ d- and f-band superconductors exhibit actual or incipient lattice instabilities as evidenced by structural transitions or anomalous dips in their phonon dispersion curves. We present a theory demonstrating that the dips and high T/sub c/'s in these materials are likely manifestations of the characteristic response (screening) by d-electrons near the Fermi level. In materials with a relatively large density of localized states at the Fermi level there is a tendency towards a collective electronic instability characterized by a periodic charge redistribution. However a charge density wave does not form because these charge fluctuations are strongly coupled to the lattice giving rise to anomalies in the phonon spectrum and in some cases eventually driving the lattice into a structural transformation. By including relaxation of the fluctuations the central peak observed by neutron diffraction in many of these materials can also be understood. In regions of q→-space where such incipient electronic instabilities are present there is lessened screening or relative enhancement of the electron-phonon matrix elements--giving rise to larger lambda's and thus greater T/sub c/'s. The details of the theory are sketched and the physical ideas explained. A simplified application of the theory to Nb and NbC shows that the positions of the dips are readily accounted for and that the size or depth of these anomalies is very sensitive to the density of states at E/sub F/. The relationship to other work is discussed