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We report on ab initio study of electron-phonon ͑e-ph͒ and electron-electron ͑e-e͒ interactions in bulk Be. The calculations show that the e-ph coupling parameter varies from 0.01 to 1.02 as a function of electron energy and momentum, = 0.21 at the Fermi level as averaged over momenta. The e-ph contribution ⌫ e-ph to the electrons and holes lifetime broadening also manifests clear dependence on the momentum and energy of an electron state. We demonstrate that the e-ph coupling matrix elements strongly affect the Eliashberg function especially for low phonon frequencies. By using the Debye model relation between ⌫ e-ph and the characteristic Debye frequency D is obtained in good agreement with the experimental one. The e-e contribution to the lifetime broadening is evaluated from the imaginary part of the electron self-energy computed within a GW approximation.

The free-electron-like surface state of Mg(0001) is strongly modified in thin films grown on W(110). The long bulk penetration length of its wave function makes it sensitive to the reflective properties of the buried interface, and hence to the complex electronic structure of the substrate. In particular we find a many-fold splitting of the Mg surface band by entering a wide projected band gap of W(110). There is a strong thickness-dependent two-band splitting, which is a clear signature of the formation of a surface-interface resonant state. An additional split-off from these two surface bands is explained by the substrate induced spin-orbit interaction.

We present ab initio calculations for the lifetime of excited electrons in transition metals. The computations were done using a pseudopotential approach in connection with a plane-wave expansion of the wave functions. The lifetimes for each element are resolved for various bands and with respect to certain directions of the crystal momentum. Our results reveal rather different trends for different transition metals showing the impossibility to work with simple models, thus emphasizing the need for first-principles calculations. DOI: 10.1103/PhysRevB.66.153101 PACS number͑s͒: 78.47.ϩp, 72.15.Lh, 71.10.Ϫw, 71.20.Gj Over the last few years the lifetime of excited electrons in metals has attracted considerable attention, both from the experimental 1-8 and the theoretical side. 9-17 While experimental studies date back to the mid 1990's, the first theoretical calculations which really took into account the explicit band structure of the investigated systems were not published until 1999. 9,10 Before this time the experimental data had to be compared to predictions based on the homogeneous electron gas ͑Fermi-liquid theory͒. 18 -20 Since then these so-called ab initio calculations have been performed for simple metals 9,12 and noble metals. [9][10][11][12][13]16 Very recently results have been presented for the averaged lifetimes for bcc and fcc transition metals. 17These calculations clearly show that a treatment from first principles is extremely important in order to explain the experimental results. As an example we just would like to mention the case of the lifetime of excited electrons in Al for which an ab initio calculation has been performed 9 and the lifetime for the various excited states was calculated. This allowed a resolution with respect to the crystal momentum ͑wave vector͒ of the states. The calculation showed that the experiment 5 -which was conducted on a polycrystalline sample-did not probe the lifetime of excited electrons in the parabolic bands which dominate the band structure of Al but rather the lifetime of states which are not free-electron-like. In other words, Fermi-liquid theory fails to explain this experiment. Another example we would like to refer to is the case of Cu. After reliable ab initio calculations 9,10,12 were not able to explain the experimental data 4 it became clear that measuring the lifetime of excited electrons using timeresolved two-photon photoemission experiments might lead under certain conditions to physical processes which cannot be explained just by electron-electron scattering and that other mechanisms 21,22 may play an important role in these cases. This analysis was only made possible because trustworthy first-principle calculations had been available.In this paper we present the calculations of the lifetime of excited electrons in six transition metals, two fcc metals ͑Rh and Pd͒, two bcc metals ͑Nb and Mo͒, and two hcp metals ͑Y and Ru͒. For all elements we present the lifetime resolved with respect to the crystal momentum of the corresponding states.In...