Difference between revisions of "Electron density map"
From Online Dictionary of Crystallography
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| + | <font color="blue">Carte de densité électronique</Font> (''Fr''). <font color="red">Elektronendichte-Karte</font> (''Ge''). <font color="black">Mappa di densità elettronica</font> (''It''). <font color="purple">電子密度図</font> (''Ja''). <font color="green">Mapa de densidad electrónica</font> (''Sp''). | ||
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== Definition == | == Definition == | ||
| − | A three-dimensional description of the electron density in a crystal structure, determined from X-ray diffraction experiments. X-rays scatter from the electron clouds of atoms in the crystal lattice; the diffracted waves from scattering planes <math>h, k, l</math> are described by [[structure factor]]s <math>\mathbf{F}_{hkl}.</math> The electron density as a function of position <math>x,y,z</math> is the Fourier transform of the structure factors: | + | A three-dimensional description of the electron density in a crystal structure, determined from X-ray diffraction experiments. X-rays scatter from the electron clouds of atoms in the crystal lattice; the diffracted waves from scattering planes <math>h, k, l</math> are described by [[structure factor]]s <math>\mathbf{F}_{hkl}.</math> The electron density as a function of position <math>x, y, z</math> is the Fourier transform of the structure factors: |
<math>\rho(xyz) = {1\over V}\sum_{hkl} F(hkl)\exp[-2\pi i(hx + ky + lz)]</math>. | <math>\rho(xyz) = {1\over V}\sum_{hkl} F(hkl)\exp[-2\pi i(hx + ky + lz)]</math>. | ||
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== Units == | == Units == | ||
| − | Electron density is measured in electrons per cubic ångström, e Å<sup> | + | Electron density is measured in electrons per cubic ångström, e Å<sup>−3</sup>. |
[[Category:Structure determination]] | [[Category:Structure determination]] | ||
[[Category:X-rays]] | [[Category:X-rays]] | ||
Latest revision as of 09:43, 13 November 2017
Carte de densité électronique (Fr). Elektronendichte-Karte (Ge). Mappa di densità elettronica (It). 電子密度図 (Ja). Mapa de densidad electrónica (Sp).
Definition
A three-dimensional description of the electron density in a crystal structure, determined from X-ray diffraction experiments. X-rays scatter from the electron clouds of atoms in the crystal lattice; the diffracted waves from scattering planes [math]h, k, l[/math] are described by structure factors [math]\mathbf{F}_{hkl}.[/math] The electron density as a function of position [math]x, y, z[/math] is the Fourier transform of the structure factors:
[math]\rho(xyz) = {1\over V}\sum_{hkl} F(hkl)\exp[-2\pi i(hx + ky + lz)][/math].
The electron density map describes the contents of the unit cells averaged over the whole crystal and not the contents of a single unit cell (a distinction that is important where structural disorder is present).
Three-dimensional maps are often evaluated as parallel two-dimensional contoured sections at different heights in the unit cell.
Units
Electron density is measured in electrons per cubic ångström, e Å−3.