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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 state is well described only with more than one (nearly-)degenerate determinant.
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.
Each single electron has a complex influence on its neighbors. The term strong correlation refers to behavior of electrons in solids that is not well-described (often not even in a qualitatively correct manner) by simple one-electron theories such as the local-density approximation (LDA) of density-functional theory or Hartree–Fock theory.
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.
(3), is the two-site two-electron Coulomb integral (It may be interpreted as the repulsive potential for electron-one at a particular point () in an electric field created by electron-two distributed over the space with the probability density ()), [a] is the overlap integral, and is the exchange integral, which is similar to the two-site ...
For the great majority of systems under study, in particular for excited states and processes such as molecular dissociation reactions, the fourth item is by far the most important. As a result, the term post–Hartree–Fock method is typically used for methods of approximating the electron correlation of a system.
[12] [13] [clarification needed] After calculating the cross-correlation between the two signals, the maximum (or minimum if the signals are negatively correlated) of the cross-correlation function indicates the point in time where the signals are best aligned; i.e., the time delay between the two signals is determined by the argument of the ...
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