Electron correlations in crystals and molecules

An expression for the Green’s function of a disordered crystal is obtained with allowance for the electron-electron interaction. The electron states of the system are described in the framework of a multiband tight-binding model. The possibility of using the proposed approach for describing the energy spectrum of molecules is demonstrated in the limit of an infinitely large primitive cell of the crystal. The energy spectrum and effective charges of atoms of a tricyanobutadienecarbazole molecule are calculated.     

Electron and atomic structure of polymers: Implication for nuclear tracks formation

A review of experimental and theoretical activities in a study of an electron and atomic structure of polymers is presented. Polymers having conjugated π-electron systems were studied experimentally in different aggregate states within the temperature interval 4.2– 300 K using spectrophotometric and spectroluminescence methods. Special attention has been paid to oxidization processes in polymers caused by ionizing radiation. The theoretical approach developed in Ukraine for electron and atomic structure calculations is based on the theory of multiple scattering of elementary excitations (electrons and phonons). This approach provides a possibility to estimate energy spectra of elementary excitations, parameters of interatomic correlations, electron density distributions, absorption and emission (photoluminescence) spectra. Study of the fluorescence spectra provides a possibility to estimate the electron structure as well as the local characteristics of latent tracks induced by nuclear particles. Dependencies of the shape of photoluminescence bands can be investigated experimentally for different kinds of nuclear particles within a wide energy range. Application of combined experimental and theoretical approach of investigation of solid-state nuclear track detector (SSNTD) physical properties, and determination of nuclear particle characteristics (charge, atomic number, etc.) are discussed.     

Thermodynamic Potential of a System of Electrons and Phonons in a Disordered Alloy

We obtain a cluster expansion for the two-time retarded Green's functions and the thermodynamic potential of a disordered crystal taking the electron–phonon and electron–electron interactions into account. The electron states of the system are described in the framework of a multiband tight-binding model. The calculations are based on the diagram techniques for the temperature Green's functions. The coherent potential approximation is chosen as a zeroth-order one-site approximation in this cluster expansion method. We show that the contributions from the processes of scattering of elementary excitations on clusters decrease as the number of sites in the cluster increases in accordance with certain small parameters. Analytic estimates of the influence of the electron–phonon interaction on the energy spectrum of electrons of an alloy being ordered are obtained in a one-band model. The applicability of these results to describing the influence of strong electron correlations on the electron structure and properties of alloys of transition metals with narrow energy bands is illustrated with the example of the Fe–Ti alloy.