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Topic: Electron density

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London forces

	Ohm's Law, Microscopic View
		Even the electron speeds are themselves small compared to the speed of transmission of an electrical signal down a wire, which is on the order of the speed of light, 300 million meters per second.
		The free electron density in a metal is a factor in determining its electrical conductivity.
		Because electrons are fermions and obey the Pauli exclusion principle, then at 0 K temperature the electrons fill all available energy levels up to the Fermi level.
	hyperphysics.phy-astr.gsu.edu /hbase/electric/ohmmic.html (755 words)

	Electron density - Wikipedia, the free encyclopedia
		Electron density is the measure of the probability of an electron being present at a specific location.
		In atoms, regions of electron density are usually found around the atom, and its bonds.
		Electron densities are sometimes probed with X-ray diffraction scans, where X-rays of a suitable wavelength are targeted towards a sample and measurements are made over time to represent, probabilistically, where electrons can be found.
	www.wikipedia.org /wiki/Electron_density (309 words)

	JCE 1997 (74) 771 [Jul] Teaching Chemistry with Electron Density Models
		Students find electron density models easy to understand and use, and because these models are easily applied to a broad range of topics, they successfully convey to students the importance of electronic structure.
		Another way to construct an electron density model of lithium is to choose a particular value of the electron density and show all points in space where the density has the chosen value.
		G.P.S. has used electron density models for several years in her general chemistry course as a tool for describing various types of bonds, and this presentation paves the way for a subsequent orbital-based description.
	jchemed.chem.wisc.edu /Journal/Issues/1997/Jul/abs771.html (4368 words)

	ROCO Electron density: definition
		According to this point of view, the electron density is a number that tells us how much charge is located at each point in the cloud.
		A wave function assigns a number to each point in space, and the numbers oscillate so that they are positive at some locations and negative at others (this behavior may remind you of the way a water wave can make a lake's surface rise at some points and fall at others).
		The following picture is a graph of the electron density in a water molecule.
	academic.reed.edu /chemistry/ROCO/Density/cloud.html (816 words)

	Fourier transforms: structure factors, phases and electron density
		In this equation, we have to divide by the volume of the unit cell to recover the electron density on the correct scale.
		The assumption that electron density is real has come in when we said that an electron at the origin scatters with a scattering factor of 1e, a real number.
		According to Parseval's theorem, the rms error in the electron density map is proportional to the rms error in the (complex) structure factor.
	www-structmed.cimr.cam.ac.uk /Course/Fourier/Fourier.html (2564 words)

	Electron Density
		The relative electron density at a set of coordinates is the electron density at those coordinates divided by the maximun electron density calculated for the plot.
		The contour plot is a two dimensional display of the regions where the values of the relative electron density lie within a specific range.
		These are the nuclear charges "seen" by electrons in the atomic orbitals that will linearly combine to form the molecular orbital.
	www.chm.davidson.edu /ronutt/che115/DensityMO/DensityMO.htm (408 words)

	Carrier densities
		The density of electrons in a semiconductor is related to the density of available states and the probability that each of these states is occupied.
		The electron density equals the hole density since the thermal activation of an electron from the valence band to the conduction band yields a free electron in the conduction band as well as a free hole in the valence band.
		For non-degenerate semiconductors one uses equations (2.6.12) and (2.6.15), while the ionized impurity densities equal the impurity density multiplied with the probability of occupancy for the acceptors and one minus the probability of occupancy for the donors.
	ece-www.colorado.edu /~bart/book/book/chapter2/ch2_6.htm (3811 words)

	UCLA PBPL - Free-Electron Laser - FEL Amplification
		When electrons are bunched together in a distance that is short compared to the wavelength of the radiation, they emit in phase, thus increasing the intensity in the emitted line and simultaneously reducing its width.
		If the electrons have the resonant velocity or are close to it, the interaction with the radiation field results in a sinusoidal modulation of the electron energy.
		The electrons emit in phase and the radiation is coherent.
	pbpl.physics.ucla.edu /Research/Theory/Free-Electron_Laser/3_-_FEL_Amplification (1384 words)

	Many-Electron Atoms - The Electronic Basis of the Periodic Table
		When the outer electron is at large distances from the nucleus and thus essentially outside of the inner shell of electron density it will experience a force from only one of the three positive charges on the lithium nucleus.
		The electron density of a d electron is concentrated even further away from the nucleus than is that of a p electron.
		Two electrons with paired spins, whether in the same or different orbitals are not prevented by the Pauli principle from being close to one another.
	www.chemistry.mcmaster.ca /esam/Chapter_4/section_3.html (2321 words)

	Botany online: Microscopy - Electron Microscopy
		The power of resolution of electron microscopy is usually restrained by the quality of the lens-systems and especially by the technique with which the preparation has been achieved.
		The degree of deflection depends on the electron density of the object.
		The scanning transmission electron microscope (STEM): In this development of the SEM do the electrons pass through the preparation and the secondary radiation thus generated is used for image formation.
	www.biologie.uni-hamburg.de /b-online/e03/03e.htm (782 words)

	[No title]
		The electron affinity of an element is the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion.
		Produced by an incident electron colliding with an atom in the specimen which is nearly normal to the incident's path.
		An electron probe is tightly focused on a TEM specimen and the resulting pattern of diffracted electrons is observed.
	www.lycos.com /info/electron--atoms.html (341 words)

	Electron Density (Site not responding. Last check: 2007-11-05)
		In both cases we have two electrons in the 1s orbital, but in the case of Li we'd expect these electrons to occupy a sphere with a smaller radius than in the case of He.
		The electron density of F must be greater than that of Li.
		Notice that fluorine actually has a higher electron density than Cl, which accounts for why the electron affinity of Cl is actually greater than that of F even though F has the smaller radius.
	neon.chem.uidaho.edu /~honors/edensity.html (303 words)

	Week 4: Electron density maps
		The electron density map is calculated from the diffraction pattern of the crystal and used to build the model.
		As a whole electron density map is pretty heavy to handle, it is advised to display only a subpart of it.
		As default the electron density will be shown in a radius of 7.5 Å of the centred atom.
	www.imsb.au.dk /~soren/PSF/Week3.html (730 words)

	3D visualization of the Laplacian of the electron density (Site not responding. Last check: 2007-11-05)
		The properties of the gradient vector field of the electron density were calculated from the wave functions prepared by the G92/DFT using AIMPAC package, [6] which was modified in our laboratory in order to perform the grid calculations in a 3D grid.
		Two of the core regions are the 1s electrons of the C and O. The negative core region of the O is hidden by valence shell electrons while the core electrons of the C are visible.
		The visible region to the right is derived from the valance shell electrons of the O. The negative region to left is derived from the valance shell electrons of the C. The valence shell of the carbon side of the O has a rather distorted shape because of the electron withdrawing effect of the oxygen.
	web.inc.bme.hu /csonka/ECCC2/paper5/lapl.html (1514 words)

	Electron Density Maps: FABP
		Amino-acids belonging to the antiparalell strand 99-113 are perfectly fitted within the electron density map.
		By decreasing the sigma value, you contour parts of the map that have a smaller electron density than when you use a high value.
		This means indeed that the electron density is badly defined in this area.
	www.usm.maine.edu /spdbv/text/fabp.htm (1062 words)

	Organic Chemistry at Penn State: Atomic Orbitals (Site not responding. Last check: 2007-11-05)
		The electron density decreases as we go farther and farther from the center, but the number of volume elements increases.
		This most probable distance of an electron from the nucleus in the hydrogen atom is in fact an atomic unit of length called bohr (what a "bore"!).
		In the contour picture the lines connect points of equal magnitude of the electron density (like on maps of mountains and valleys where points of equal altitude are connected by lines).
	courses.chem.psu.edu /chem38/mol-gallery/orbitals/orbitals.html (850 words)

	Theory of Atoms in Molecules: The Laplacian of the Electron Density and the Lewis and VSEPR Models
		Theory of Atoms in Molecules: The Laplacian of the Electron Density and the Lewis and VSEPR Models
		The Laplacian of the electron density recovers the shell structure of an atom by displaying a corresponding number of alternating shells of charge concentration and charge depletion.
		The use of the Laplacian of the electron density to account for the bent geometries of the hydride, halide and methylide molecules of calcium, strontium and barium, in terms of a distortion of the outer core of the electron density of the metal atom is discussed in reference 12.
	www.chemistry.mcmaster.ca /faculty/bader/aim/aim_5.html (984 words)

	[No title]
		*Density of states derivable from assumption that, for high quantum numbers, the number of distinct E levels for E
		The total energy of a system can be expressed as a functional of the density and this functional is minimized by the ground state density.
		Besides the expansion of molecular orbitals in finite basis sets, there are issues of adequate representations of the electron density and the exchange correlation potential.
	www.sdsc.edu /~kimb/dft_lecture.html (1259 words)

	Electron Energy Density (Site not responding. Last check: 2007-11-05)
		The behavior of electrons in solids depends upon the distribution of energy among the electrons:
		This distribution determines the probability that a given energy state will be occupied, but must be multiplied by the density of states function to weight the probabability by the number of states available at a given energy.
		This represents the number of electron states per unit volume per unit energy at energy E. This energy density is a factor in many of the electical properties of solids.
	hyperphysics.phy-astr.gsu.edu /hbase/quantum/eedens.html (282 words)

	Molecular Surfaces: Electron Density Fitting
		The main problem in electron density fitting is that moving two different, but connected parts of the molecule into their appropriate electron density may cause these two parts not to join properly (e.g.
		The model and density are made to appear three dimensional by various methods: stereo pairs, rotation interactively controlled by analog input device, and intensity depth cueing.
		Atoms are positioned into the density by (1) moving entired residues, (2) rotating around torsional angles, (3) regularizing using a method developed by Jan Hermans and John McQueen, (4) the MOVE command, which moves an atom to where on wants it.
	www.netsci.org /Science/Compchem/feature14c.html (1513 words)

	Stefan Birner: Density of states (Essay)
		The motion of the electrons is in the
		/L. To calculate the density of states the number of wavevectors in the shaded circular ring between k and k+dk must be determined.
		One of the failures of the free electron theory was that the heat capacity of the electrons was
	www.asamnet.de /~birners/public_html/density.html (953 words)

	X-Ray Crystallography Notes (Site not responding. Last check: 2007-11-05)
		From some simple calculations using density, chemical formula, and Avogadro's number, researchers of the time were able to show that simple crystals should have repeating units of the size needed for their proof of the wave-like nature of X rays.
		Because the scattered intensity is inversely proportional to the square of the mass of the particle emitting the X-ray photon, scattering of X rays from the nucleus is considered negligible compared to the scattering from the electrons of an atoms.
		The electron density used in the structure factor expression is related to the types and positions of the atoms in the unit cell.
	xrayweb.msg.ku.edu /notes/crystallography.html (5053 words)

	Electron density modification with Solomon
		One should realise that the solvent will have a mean electron density which is very similar to that of the protein, and that solvent and protein are mainly distinguished by the relative featurelessness of the former, and the undulating landscape of the latter.
		As a result of truncating the density within the protein region, the overall variance of electron density of the protein region relative to the solvent region decreases.
		This means that the density of the solvent region has to be scaled down since it was found desirable to maintain a constant ratio between the two.
	www.ccp4.ac.uk /newsletters/newsletter/solomon.html (1928 words)

	Volslice3D: Visualization of Electron Density Maps
		The maximum density value (mxd) is represented white and the minimum density value (mnd) is represented fl.
		Red corresponds to negative density values (color levels increase with absolute density value and are normalized by the maximum of -mnd, mxd).
		RYG: The densities are mapped to a red-yellow-green gradient (linear interpolation from mnd to mxd).
	www.fz-juelich.de /vislab/virtual/volslice3d/use.html (816 words)

	The Orbitron: a gallery of atomic orbitals and molecular orbitals
		The "surface" of the orbital represents points for which the electron density for that orbital is the same - an isosurface.
		By choosing different values of electron density, denoted by the bar moving up and down on the line plot or by the moving plane on the surface plot, then the size of the 3d plot changes.
		This plot also shows that the magnitude of the electron density for the inner lobes is high so that if we choose a high threshold value (when the bar is high), then we only see one or more of the inner lobes in the three-dimensional plot.
	www.shef.ac.uk /chemistry/orbitron/AOs/5g/e-density.html (206 words)

	ippex online
		The electron density is the number of electrons per unit volume.
		The central electron density (the density in the center of the plasma) is important since it is in the center where most fusion reactions take place.
		A plasma is composed of ions and free electrons.
	ippex.pppl.gov /fusion/glossary.html (868 words)

	MAIN Command Reference Manual:Electron density modifications
		Electron density can be manipulated by any mean that will yield a more interpretable electron density map, finally resulting in a completly resolved and refined structure of a macromolecule.
		The procedure is repeated until the apparent R-factor of the electron density map converges The aim is to produce an interpretable electron density map.
		Electron density averaging requires clear boundaries between protein and solvent volumes, it should be almost inevitably preceded by a solvent flattening in the case of multiple isomorphous replacement phase evaluation.
	www.hhmi.swmed.edu /Manuals/main/dens_mod/dens_mod.html (6650 words)

	Focus of Research in the Ashoori Group
		Systems in which electrons exist purely in two or one dimensions and even small boxes (quantum dots) containing as few as one electron can now be produced with relative ease.
		While simple quantum mechanical calculations determine the motion of a single electron in such a confining structures, it is far from simple to understand the behavior of many trapped electrons.
		At high magnetic fields, the electron density in the artificial atom even undergoes a bifurcation into discrete inner and outer shells with low electron density between the shells.
	electron.mit.edu /overview (1734 words)

	2.7 Doped Semiconductors
		The hole concentration in equilibrium is written as a function of the electron density by using the mass action law.
		The electron and hole densities are then written as a function of the Fermi energy using the expressions for non-degenerate semiconductors, while the ionized impurity densities equal the impurity density multiplied with the probability of occupancy for the acceptors and one minus the probability of occupancy for the donors, yielding:
		The value for the Fermi energy and carrier density is obtained at the crossing (indicated by the arrow) of the two fl curves which represent the total positive and total negative charge in the semiconductor.
	ece-www.colorado.edu /~bart/book/extrinsi.htm (1440 words)

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