S. I. Simak

Random conductivity of δ-Bi2O3 films

The experimental investigation of the cubic δ-Bi2O3 phase grown on a (110) Au substrate at low temperature has disclosed a chaotic character of the conductivity at low voltage and temperature. Based on first-principles calculations, we show that the conductivity of this oxide strongly depends on the distribution of oxygen ions and that oxygen migration is able to cause a momentary switch of the conduction mechanism.

Electronic topological transitions in the AgPd system

Abstract “First-principles” LMTO-CPA calculations of the Fermi surfaces and thermodynamic properties of Ague5f8Pd random alloys are presented. We show that there are at least four electronic topological transitions (ETT) in the system. The changes of the Fermi surface topology lead to the appearance of peculiarities in the concentration dependence of the thermodynamic (ground state) properties.

Pressure-induced change of the Fermi surface topology in Al-based solid solutions

An ab initio study of the electronic structure and the Fermi surface is carried out for random Al-Si and Al-Ge solid solutions. At a 10 at. % Si content, a topological transition of the neck-formation type is revealed, which can account for the experimentally observed peculiarities of the transport properties of the Al-Si system. A similar transition is also found in the Al-Ge system, and the appearance of the anomalous transport coefficients at Ge concentrations of about 10 at. % is predicted. In addition, it is shown that the increase in the concentration of the dopants gives rise to nesting of the Fermi surface sheets (superposition of electron-hole pockets). This peculiarity of the Fermi surface can be responsible for the enhancement of the superconductivity and the instability of the crystal structure observed in the Al1−xSix and Al1−xGex solid solutions.

Exchange coupling in Fe/(Mo1-x Re x ) n /Fe (100) and (110) multilayers

Abstract The exchange coupling in sandwiches of layers of pure bcc Mo and random bcc MO88Re12 embedded in an Fe matrix has been studied by the first-principles Green function technique. We have calculated up to 20 layers of the spacer material for the planes (100) and (110) and obtained oscillation periods. The exchange coupling amplitude and periodicity are analysed with respect to two effects: (i) the interface orientation and (ii) the electronic topological transitions (ETTs), resulting in an essential difference between the Fermi surfaces of Mo88Re12 and pure Mo.

Total Energy Calculations of Alloys: Locally Self-Consistent Green’s Function Method

There is a growing interest in first-principles investigations of materials with broken translational symmetry, for example, impurities, interfaces, and alloys. In particular, the total energy and the electronic structure calculations of systems with an arbitrary distribution of atoms on an underlying lattice will give information essential to understanding their stability and properties. At the same time two schemes most frequently used in ab initio total energy calculations for completely random alloys, the ConnollyWilliams (CW) method1 and the methods based on the single-site approximation, as the coherent potential approximation (CPA)2, have limited applicability and reliability3. Another way of approaching the solution to the electronic structure problem for disordered systems is given by the supercell technique. In this case the three-dimensional periodicity is restored although its effect on the final result can be neglected. Then conventional band structure methods can be used. However, this approach has both fundamental and technical limitations. For instance, from the basic point of view all details connected with the smearing of the electronic spectrum and the Fermi surface in alloys are lost. From the technical point of view the computational effort increases as N 3 with increasing number of atoms N in the supercell.