Computational Chemistry and Molecular Modeling
Atomic, Molecular and Optical Physics
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Band structure with a quasicontinuum of electronic states near the Fermi surface (FS) of a solid-state matter indicates overlapping regions of the electronic and phonon spectra: (εP - εQ) ≈ ℏωv. This simple fact has an important impact on the theoretical aspects of the description and a study of an electronic structure and physical properties of a matter since velocities of the nuclei and electrons are on the same scale. The motion of the electrons is not adiabatic and the description of the electronic structure of a system cannot be based on the assumption of the validity of Born-Oppenheimer approximation. For nonadiabatic systems in contrast to the descripton of adiabatic systems [(εp - εQ) 〉 ℏωv], an effect of the finite mass of the electrons, i.e.· nonadiabatic corrections, cannot be calculated by a perturbation theory due to the divergency of a perturbation expansion. Quasiparticle transformation technique has disclosed the unexpected effects of nonadiabaticity on the electronic structure and physical properties of matter. The aspects of superconductivity are discussed. © 1993 John Wiley & Sons, Inc.
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