Point charge model

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The point charge model is a greatly simplified description of charge distributions in that it is assumed that the charge is present at a point without any spatial expansion. It is used in the description of molecular binding forces and in particular of electric fields in crystals , predominantly ion crystals, in order to calculate electric field gradients and nuclear quadrupole moments . In ion crystals, charged atoms ( ions ) and point defects are considered to be essential charge carriers. The total charge of the ion or point defect is assumed to be in the center of the atom without considering the charge distribution within the atom itself. In the point charge model, it is assumed that the total charge of the ion or the point defect carries the majority for an observed electric field gradient. This simplification is valid within a limited framework for ions with closed shells (f-, d-, p-shell) and when the charge is in the spherical s-shell (see atomic orbital ). It is not uncommon for the deviations between the point charge model and measurements to be greater than 50%. As soon as f-, d- or p-shells are partially occupied, the deviations can be significantly larger.

The point charge model was used in the beginnings of solid-state physics and solid-state chemistry, before the advent of powerful computers, to calculate electric field gradients that were compared with measurements from methods of nuclear solid-state physics , such as: B. Mössbauer spectroscopy and disturbed gamma-gamma angle correlation . Today the very computationally intensive calculations are carried out almost exclusively with the density functional theory , which also takes the charge distribution of the atom and its bonds into account and delivers significantly improved results.

Individual evidence

  1. ↑ Zeitschrift für Naturforschung A, Volume 33, Issue 9, Pages 1056-1061, ISSN (Online) 1865-7109, ISSN (Print) 0932-0784, DOI: https://doi.org/10.1515/zna-1978-0911 .
  2. ↑ J. Chem. Phys. 108: 6722 (1998); https://doi.org/10.1063/1.476088