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Concept
Modèle de l'électron quasi libre
Résumé
In solid-state physics, the nearly free electron model (or NFE model and quasi-free electron model) is a quantum mechanical model of physical properties of electrons that can move almost freely through the crystal lattice of a solid. The model is closely related to the more conceptual empty lattice approximation. The model enables understanding and calculation of the electronic band structures, especially of metals.
This model is an immediate improvement of the free electron model, in which the metal was considered as a non-interacting electron gas and the ions were neglected completely.
The nearly free electron model is a modification of the free-electron gas model which includes a weak periodic perturbation meant to model the interaction between the conduction electrons and the ions in a crystalline solid. This model, like the free-electron model, does not take into account electron–electron interactions; that is, the independent electron approximation is still in effect.
As shown by Bloch's theorem, introducing a periodic potential into the Schrödinger equation results in a wave function of the form
where the function has the same periodicity as the lattice:
(where is a lattice translation vector.)
Because it is a nearly free electron approximation we can assume that
where denotes the volume of states of fixed radius (as described in Gibbs paradox).
A solution of this form can be plugged into the Schrödinger equation, resulting in the central equation:
where the kinetic energy is given by
which, after dividing by , reduces to
if we assume that is almost constant and
The reciprocal parameters and are the Fourier coefficients of the wave function and the screened potential energy , respectively:
The vectors are the reciprocal lattice vectors, and the discrete values of are determined by the boundary conditions of the lattice under consideration.
In any perturbation analysis, one must consider the base case to which the perturbation is applied. Here, the base case is with , and therefore all the Fourier coefficients of the potential are also zero.
Source officielle
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Concepts associés (12)
Modèle de l'électron libre
En physique du solide, le modèle de l'électron libre est un modèle qui sert à étudier le comportement des électrons de valence dans la structure cristalline d'un solide métallique. Ce modèle, principalement développé par Arnold Sommerfeld, associe le modèle de Drude aux statistiques de Fermi-Dirac (mécanique quantique). Électron Particule dans réseau à une dimension 2.4 Modèle de sommerfeld ou de l'électron libre dans un puits de potentiel, sur le site garmanage.com Catégorie:Physique du solide Catégorie:É
Jellium
Jellium, also known as the uniform electron gas (UEG) or homogeneous electron gas (HEG), is a quantum mechanical model of interacting electrons in a solid where the positive charges (i.e. atomic nuclei) are assumed to be uniformly distributed in space; the electron density is a uniform quantity as well in space. This model allows one to focus on the effects in solids that occur due to the quantum nature of electrons and their mutual repulsive interactions (due to like charge) without explicit introduction of the atomic lattice and structure making up a real material.
Independent electron approximation
In condensed matter physics, the independent electron approximation is a simplification used in complex systems, consisting of many electrons, that approximates the electron-electron interaction in crystals as null. It is a requirement for both the free electron model and the nearly-free electron model, where it is used alongside Bloch's theorem. In quantum mechanics, this approximation is often used to simplify a quantum many-body problem into single-particle approximations.
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