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Electron correlation is sometimes divided into dynamical and non-dynamical (static) correlation. Dynamical correlation is the correlation of the movement of electrons and is described under electron correlation dynamics [3] and also with the configuration interaction (CI) method. Static correlation is important for molecules where the ground ...
These effects are often collectively used as a definition of the term electron correlation. However, the label "electron correlation" strictly spoken encompasses both the Coulomb correlation and Fermi correlation, and the latter is an effect of electron exchange, which is fully accounted for in the Hartree–Fock method.
Correlation functions are typically measured with scattering experiments. For example, x-ray scattering experiments directly measure electron-electron equal-time correlations. [7] From knowledge of elemental structure factors, one can also measure elemental pair correlation functions. See Radial distribution function for further information.
In contrast to the Hartree–Fock method, in order to account for electron correlation, CI uses a variational wave function that is a linear combination of configuration state functions (CSFs) built from spin orbitals (denoted by the superscript SO),
[4]: p.712 For example, if a positive charge is brought near the object (see picture of cylindrical electrode near electrostatic machine), the electrons in the metal will be attracted toward it and move to the side of the object facing it. When the electrons move out of an area, they leave an unbalanced positive charge due to the nuclei.
To understand how the SCE system is constructed, it is useful to first think in terms of a simple example. Consider a collection of identical classical charges (with repulsive Coulomb interaction) confined in some container with a given shape. If let alone, the charges will distribute themselves within the container until they reach the spatial ...
Drude applied the kinetic theory of a dilute gas, despite the high densities, therefore ignoring electron–electron and electron–ion interactions aside from collisions. [Ashcroft & Mermin 13] The Drude model considers the metal to be formed of a collection of positively charged ions from which a number of "free electrons" were detached.
As a result, the term post–Hartree–Fock method is typically used for methods of approximating the electron correlation of a system. Usually, post–Hartree–Fock methods [ 3 ] [ 4 ] give more accurate results than Hartree–Fock calculations, although the added accuracy comes with the price of added computational cost.