This is the case when electron correlation is large.

Many types of calculations ( known as post-Hartree – Fock methods ) begin with a Hartree – Fock calculation and subsequently correct for electron – electron repulsion, referred to also as electronic correlation.

The first-order energy is the Hartree – Fock energy and electron correlation is included at second-order or higher.

The simplest approximation is the local-density approximation ( LDA ), which is based upon exact exchange energy for a uniform electron gas, which can be obtained from the Thomas – Fermi model, and from fits to the correlation energy for a uniform electron gas.

It essentially takes the basic Hartree – Fock molecular orbital method and constructs multi-electron wavefunctions using the exponential cluster operator to account for electron correlation.

The method was initially developed by Fritz Coester and Hermann Kümmel in the 1950s for studying nuclear physics phenomena, but became more frequently used when in 1966 Jiři Čížek ( and later together with Josef Paldus ) reformulated the method for electron correlation in atoms and molecules.

This improves the treatment of dynamical electron correlation by satisfying the Kato cusp condition and accelerates convergence with respect to the orbital basis set.

Effects arising from deviations from this assumption, known as electron correlation, are completely neglected for the electrons of opposite spin, but are taken into account for electrons of parallel spin.

( Electron correlation should not be confused with electron exchange, which is fully accounted for in the Hartree – Fock method.

Neglecting electron correlation can lead to large deviations from experimental results.

A number of approaches to this weakness, collectively called post-Hartree – Fock methods, have been devised to include electron correlation to the multi-electron wave function.

The EFG couples with the nuclear electric quadrupole moment of quadrupolar nuclei ( those with spin quantum number greater than one-half ) to generate an effect which can be measured using several spectroscopic methods, such as nuclear magnetic resonance ( NMR ), electron paramagnetic resonance ( EPR, ESR ), nuclear quadrupole resonance ( NQR ), Mössbauer spectroscopy or perturbed angular correlation ( PAC ).

The emphasis in the program is on highly accurate computations, with extensive treatment of the electron correlation problem through the multireference configuration interaction, coupled cluster and associated methods.

Integral-direct local electron correlation methods reduce the increase of the computational cost with molecular size.

The resulting energies are more competitive, with energies from calculations where electron correlation is introduced based on a Hartree – Fock reference wavefunction.

Other important experiments studied the angular correlation between electron-positron pairs in neutral pion decays, and established the rare decay of a charged pion to an electron and neutrino ; the latter required use of a liquid-hydrogen bubble chamber.

Taube felt that a " primary flaw " with his correlation between electron configuration and ligand substitution was that it was described mainly in terms of valence bond theory, as crystal field theory and ligand field theory were not well established when he published his work in 1952.

Its major strength is the accurate calculation of atomic and molecular energies as well as properties using many-body techniques such as many-body perturbation theory ( MBPT ) and, in particular coupled cluster techniques to treat electron correlation.

The theory uses second-order perturbation theory to describe an indirect exchange coupling whereby the nuclear spin of one atom interacts with a conduction electron via the hyperfine interaction, and this conduction electron then interacts with another nuclear spin thus creating a correlation energy between the two nuclear spins.

The PPP formulation is actually an approximate pi-electron effective operator, and the empirical parameters, in fact, include effective electron correlation effects.

Importantly, because the Fock operator is a one-electron operator, it does not include the electron correlation energy.

As with carbenes, a strong correlation exists between the spin density on the nitrogen atom which can be calculated in silico and the zero-field splitting parameter D which can be derived experimentally from electron spin resonance.

Crystallographers often explicitly state the type of illumination used when referring to a method, as with the terms X-ray diffraction, neutron diffraction and electron diffraction.

The name klystron comes from the stem form κλυσ-( klys ) of a Greek verb referring to the action of waves breaking against a shore, and the end of the word electron.

In physics and chemistry, the Lyman series is the series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1 ( where n is the principal quantum number referring to the energy level of the electron ).

It has uses in determining possible electron re-configuration when referring to reaction mechanisms, and often results in the same sign as the partial charge of the atom, with exceptions.

Hameroff, however, claims that he is referring to the behaviour of two or more electron clouds ; secondly McKemmish shows that changes in tubulin conformation driven by GTP conversion would result in a prohibitive energy requirement.

When quantum mechanics refers to the orbital angular momentum of an electron, it is generally referring to the spatial wave equation that represents the electron's motion around the nucleus of an atom.

MeV and meV are multiples and submultiples of the electron volt unit referring to 1, 000, 000 eV and 0. 001 eV, respectively.

Argus proved the validity of Christofilos theory: the establishment of an electron shell derived from neutron and β-decay of fission products and ionization of device materials in the upper atmosphere was demonstrated.

Feynman diagrams | Feynman diagram elementsThese actions are represented in a form of visual shorthand by the three basic elements of Feynman diagrams: a wavy line for the photon, a straight line for the electron and a junction of two straight lines and a wavy one for a vertex representing emission or absorption of a photon by an electron.

Diagram representing an electron ionization ion source

An image dissector, also called a dissector tube, is a video camera tube in which photocathode emissions create an " electron image " which is then scanned to produce an electrical signal representing the visual image.

The electron multiplier or aperture permits only those electrons emanating from a very small area of the electron image, representing a similarly small area of the visual image.

Brenner's team sliced worms into thousands of ultrathin sections and photographed every section under an electron microscope, then visually matched fibers from section to section, to map out every neuron and synapse in the entire body.

In this " condensed " state, the breaking of one pair will change the energy of the entire condensate-not just a single electron, or a single pair.

The diamagnetism in this configuration arises from the single unpaired electron on superoxide aligning antiferromagnetically from the single unpaired electron on iron, to give no net spin to the entire configuration, in accordance with diamagnetic oxyhemoglobin from experiment.

The key limitation of electron beam lithography is throughput, i. e., the very long time it takes to expose an entire silicon wafer or glass substrate.

Thus the magnitude of the shift is related not to the Compton wavelength of the electron, but to the Compton wavelength of the entire atom, which can be upwards of 10 000 times smaller.

The primary advantages to the electron microscope based technique is the ability to resolve features down to 1 nanometer, the ability to measure an entire spectrum at each point ( hyperspectral imaging ) if the photomultiplier tube is replaced with a CCD camera, and the ability to perform nanosecond-to picosecond-level time-resolved measurements if the electron beam can be " chopped " into nano-or pico-second pulses.

In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap.

With a framebuffer, the electron beam ( if the display technology uses one ) is commanded to trace a left-to-right, top-to-bottom path across the entire screen, the way a television renders a broadcast signal.

When ionizing radiation is emitted by or absorbed by an atom, it can liberate a particle ( usually an electron, but sometimes an entire nucleus ) from the atom.

In de-localized or conjugated systems, such as phenol, benzene and compounds such as hemoglobin and chlorophyll, the electron density covers an entire region, i. e., in benzene they are found above and below the planar ring.

Einstein believed that there might be an asymmetry between the charges of the electron and proton so that the Earth's magnetic field would be produced by the entire Earth.

Brenner's team sliced worms into thousands of ultrathin sections and photographed every section under an electron microscope, then visually matched fibers from section to section, to map out every neuron and synapse in the entire body.

The entire electron image is deflected and a scanning aperture permits only those electrons emanating from a very small area of the photocathode to be captured by the detector at any given time.

The electron image is periodically deflected horizontally and vertically (" raster scanning ") such that the entire image is read by the detector many times per second, producing an electrical signal that can be conveyed to a display device, such as a CRT monitor, to reproduce the image.

Valence bond theory now complements molecular orbital ( MO ) theory, which does not adhere to the VB idea that electron pairs are localized between two specific atoms in a molecule but that they are distributed in sets of molecular orbitals which can extend over the entire molecule.

The key limitation of electron beam lithography is throughput, i. e., the very long time it takes to expose an entire silicon wafer or glass substrate.

The systems work either by scanning the entire picture a dot at a time and modulating the laser directly at high frequency, much like the electron beams in a cathode ray tube, or by optically spreading and then modulating the laser and scanning a line at a time, the line itself being modulated in much the same way as with Digital Light Processing ( DLP ).

The simplest conception is that a light quantum transfers its entire energy to a single electron [...]

Ecstasy, says Charon, is the higher level of excitement felt when the electron fills one plane with photon energy, to the threshold at which it jumps to the next quantum level — ignites, until the entire system is fully energized.