Properties of atoms in crystals: Dielectric polarization

It is shown that the polarization of a molecule or an extended system, permanent or induced can, like all measurable properties, be equated to a sum of atomic contributions. While it has been previously shown that a change in the polarization of a dielectric can be considered a consequence of a geometric quantum phase and obtainable from a Berry phase in a parameter space, such a possibility does not exclude a real space description, stated in terms of the charge distributions of the system's composite atoms or cells. The cells are defined as bounded regions of real space whose properties are described by the physics of a proper open system, a description that applies to any system regardless of the nature of the interactions between the atoms. This approach necessarily leads to the inclusion of a contribution to the polarization arising from the transfer of charge across the boundary of a cell, in addition to that from the cell's internal polarization, thereby correcting the textbook description of polarization that considers only the latter contribution. It is shown that a neutral repeating cell in a dielectric behaves as an atomic capacitor which mimics the macroscopic behavior, with the internal charge transfer leading to the creation of what Feynman terms the "surface polarization charge." (C) 2001 John Wiley & Sons, Inc.