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"> | ||
+ | Elektron-Dichte-Karte</Font> (''Ge''). <Font color="green">Mapa de densidad electrónica</Font> (''Sp''). <Font color="black"> Mappa di densità elettronica</Font> (''It''). <Font color="purple">電子密度図</Font> (''Ja'') | ||
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== Definition == | == Definition == | ||
Revision as of 04:43, 20 March 2015
Carte de densité électronique (Fr). Elektron-Dichte-Karte (Ge). Mapa de densidad electrónica (Sp). Mappa di densità elettronica (It). 電子密度図 (Ja)
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.