Using the full potential (LAPW) band structure method, a detailed investigation of the structural and magnetic phase stability of VS and VSe has been performed. In full accordance with experiment, the MnP-structure was found to be the equilibrium phase for VS at low temperature. The changes in the electronic structure that accompany the phase transition from the orthorhombic MnP-structure to the hexagonal NiAs-structure is monitored using the dispersion relations, the density of states curves as well as the electronic charge density distribution. For VSe in the NiAs-structure the magnetic phase diagram as a function of the hexagonal lattice parameters a and c has been determined. In agreement with experiment, the anti-ferromagnetic phase was found to be energetically the most favourable one among the para-, ferro- and anti-ferromagnetic phases.

A detailed study of the electronic structure of Nb3Te43As, for x = 0, 0.5 and 1.0 using core level X-ray photoelectron spectroscopy and valence band ultraviolet photoelectron spectroscopy is presented. Using He I and He II radiation, pronounced changes in the spectra upon replacing Te by As are found in the region close to the Fermi energy. These changes are explained on the basis of the electronic band structure calculations using the linear muffin tin orbital method. In addition, these calculations clearly demonstrate the change from quasi-one- to three-dimensional behavior upon going from Nb3Te4 to Nb3Te3As. This is in line with results of resistivity measurements presented, as well as previous X-ray single crystal investigations. Down to 1.5 K no transition into the superconducting state is observed.

The ternary compound ZrSiTe is a metal with the majority of the emission at the Fermi level due to Zr d-states. It is noteworthy that Si as wen as Te states significantly contribute to the DOS at E(F). Small chemical shifts of the core levels are indicative of only small charges on the different atoms. The calculation of the experimental bandstructure supports the conclusions drawn from the experimental valence band spectra. In addition, the results exhibit that the bonding interactions are strong within the layers and only weak perpendicular to the layers. Hence, the material is not a ''true'' two-dimensional layer compound, but it is rather weakly three dimensional.