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Based on the self-consistent band structure we present density-of-states (DOS) functions for a supercell structure (SnS)(1.2)NbS2 and discuss the intercalation effects. An ab initio UPS spectrum of (SnS)NbS2 is compared to the experiment. The prototypes of the layer constituents of the misfit, PbS (NaCl) and 2H-NbS2 and NbSe2, are studied; theoretical results are compared with available XPS and optical measurements. For PbS both relativistic effects and local field effects are found important. Experimental angle resolved UPS for NbSe2 are compared to k(parallel to)-projected DOS functions. (C) 2001 Elsevier Science B.V. All rights reserved.

Electron spectroscopy at low kinetic energies, e.g., valence band photoemission with vacuum ultraviolet light, is sensitive to the fine structure of the electron damping, i.e., to the magnitude and energy dependence of the optical potential. The basis of this quantity is usually given by a semiquantitative analytical derivation together with empirical findings from the escape depth. Only recently the optical potential has been determined ab-initio via calculating the self-energy. Here, this approach is used to calculate the self-energy and from this the wave functions in the conduction band regime with scattering boundary conditions for the surface system. For the former, the GW approximation is applied. For the latter, algebraic solvers in the Laue representation have been used to solve the Schrodinger equation for arbitrary potentials. The wave function is investigated to extract physical quantities, like the angle and energy dependent escape depth, which are significant in discussing electron scattering.

A different class of layered systems derived from ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type materials is introduced and studied. We present preparation, x-ray analysis, band-structure, and total-energy calculations of ${\mathrm{KCu}}_{2}{\mathrm{Se}}_{2},$ a semimetallic representative of this class. The crystal has an orthorhombic symmetry by a slight distortion of a tetragonal lattice. From calculation, interesting quasi-two-dimensional electronic properties are obtained similar to those of the well-known hexagonal transition-metal dichalcogenides. A complex picture of chemical bonding in this mixed-valency compound is elucidated by electronic structure calculations. The changes in the band structure caused by the symmetry reduction and their implications for the total energy are discussed. The ab initio band-structure calculation is performed with the extended linear augmented plane-wave $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ method, with all the states down to $\mathrm{K}3s$ being treated as valence states. The total energy is computed using the augmented Fourier component representation of the crystal potential.

A theoretical study of the optical excitation processes in cetineites is presented. This new exciting class of crystals with tubular structures displays photoconductivity, which strongly depends on the presence of guest molecules within the tubes. Based on self-consistent electronic structure calculations we present calculated dielectric function and photoelectron spectra of the (Na;Se) cetineite with the tube fllled with different guest molecules. Calculations are performed with the extended linear augmented plane wave kp method. The configuration and the arrangement of the filling molecules is derived from available crystallographic data and from heuristic arguments on chemical binding.

A recently developed method for treating scattering states is further investigated and extended. It yields the wave functions as used, for example, in a calculation for electron diffraction at very low energies or for photoemission in the one-step model at vacuum-ultraviolet photon frequencies. The necessity of non-muffin tin potentials at these energies for covalent bond solids is obvious. The method uses a Laue representation, as well as the full direct space, applying also multigrid techniques.