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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.
A stronger correlation between the X-ray measured diffracted intensities and quantum mechanical wavefunctions is possible using the wavefunction based methods [16] of Quantum Crystallography, as for example the X-ray atomic orbital model, [17] the so-called experimental wavefunction [18] or the Hirshfeld Atom Refinement. [19]
The model also explains partly the Wiedemann–Franz law of 1853. Drude formula is derived in a limited way, namely by assuming that the charge carriers form a classical ideal gas. When quantum theory is considered, the Drude model can be extended to the free electron model, where the carriers follow Fermi–Dirac distribution. The conductivity ...
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),
The Hubbard model introduces a contact interaction between particles of opposite spin on each site of the lattice. When the Hubbard model is used to describe electron systems, these interactions are expected to be repulsive, stemming from the screened Coulomb interaction. However, attractive interactions have also been frequently considered.
The effects of electron correlation, beyond that of exchange energy resulting from the anti-symmetrization of the wavefunction, are completely neglected. 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.