The Interplay of Long Range Interactions and Electron Density Distributions in Polar and Strongly Correlated Materials

Abstract

In the present contribution, we summarize the recent theoretical results on the physics of the electron-TO-phonon (el-TO-ph) interaction in polar materials. Within the frameworks of dipole approximation, we linked the interaction of electrons with the long-wavelength transverse optical vibrations to the long-range dipole-dipole interaction. We suggested a macroscopic parameterization of the el-TO-ph coupling constants in terms of experimental material parameters relating to phonon and electron characteristics of the system. The parametrization enabled us to introduce a novel relation that may measure a degree of polarity, and may indicate how close the dielectric behavior of the system is to a structural instability. The ferroelectric tendencies of known crystalline compounds were reproduced. Further considerations were focused on an integrated analysis of charge, electronic, and vibrational properties of iron-based narrow-gap systems FeSi and FeAs2. Similarly to ferroelectrics, these materials demonstrate a strong interplay of electronic and polarization degrees of freedom, which is mediated by the dynamic hybridization of the relevant frontier orbitals.