Model of the quasi-free electrons
The nearly free electron model ( Engl. Nearly-free electron model by its author, often abbreviated to NFE model), Felix Bloch and Bloch theory called, is a theoretical model in solid-state physics to describe conduction and valence electrons in solids . It extends the model of free electrons with a weak periodic electrostatic potential for an approximate description of the positively charged atomic cores in the crystal lattice . First you set the periodicity of theEnergy bands in the reciprocal space , which have a band gap at the zone boundaries when a small lattice potential is taken into account . The display takes place in an extended, reduced or periodic zone scheme .
Even this very simple improvement allows a theoretical prediction of the band gap and thus a division of the solids into electrical conductors , semiconductors and insulators . The model of the quasi-free electrons forms the foundation of the ribbon model .
As in the free electron model, the approximation of independent electrons still persists; This means that the electrical interactions between the electrons are not taken into account. Phenomena based on this, such as superconductivity, cannot be described with this model.
See also
literature
- Neil W. Ashcroft, N. David Mermin: Solid State Physics . 2nd Edition. Oldenbourg, Munich 2005, ISBN 3-486-57720-4 .