Electron left-right type

Consider the semiconductor device below which is hooked up to a battery (direct current). The n-type semiconductor (a) is connected to the negative terminal of a battery, the p-type to the positive terminal. This has the effect of pushing conduction electrons from right to left and positive holes from left to right. 

Fig. 18.1 Modus operandi of n-type (top left), p-type (top right), and tandem DSSCs (bottom). SA and SD are acceptor and donor dyes, respectively. Ef, cb, and vb are Fermi level, conduction band, and valance band, respectively, e and h+ refer to electron and hole current, respectively.

Figure 5.5. Types of electron momentum densities no(p) >n atoms. Solid lines are used for the total density, whereas dotted lines and crosses indicate the contribution from the outermost s and p orbitals, respectively. Top left a type I density for the potassium atom. Top right a typical type II density for the argon atom. Bottom left a typical type III density for the silver atom. Bottom right a closeup of rio(p) for the silver atom showing the minimum and secondary maximum. Adapted from Thakkar [29].

The importance and physical nature of dynamic correlation is even better appreciated in the case of 3e bonds, a type of bond in which the electron correlation is entirely dynamic, since there is no left-right correlation associated with odd-electron bonds. As noted earlier, the Hartree Fock and simple VB functions for 3e bonds (hence, GVB, SC, or VBSCF) are nearly equivalent and yield about similar bonding energies. Taking the F2 radical anion as an example, it turns out that, compared to the experimental bonding energy of... 

The essential part of non dynamical correlation energy for polyatomic molecules is the left-right electron correlation , which is concerned with the ionic-covalent balance within a given two-electron bond. Let us therefore discuss this type of correlation. 

Fig. 19.3. Types of electron momentum densities Uip) — Hgip) in atoms. Solid lines are used for the total density. Left a Type 1 density for the beryllium atom the contribution from the 2s orbital is indistinguishable from the total density. Right a typical Type 11 density for the neon atom the 2s and 2p contributions are shown as dashed and dotted lines, respectively.

The importance and physical nature of dynamic correlation is even better appreciated in the case of three-electron bonds, a type of bond in which the electron correlation is entirely dynamic, since there is no left-right correlation... 

NBOs also underlie novel methods for describing electron correlation in localized terms. A starting NBO configuration can be used to construct localized multi-configurational CAS/NBO wavefunctions with transferable correlation contributions corresponding to the familiar types (left-right, in-out, angular) in diatomic molecules. 

Wave function (3) or (4) contains left-right correlation which is necessary for a correct de.scription of the dissociation of the H2 molecule. It yields 85% of the observed value of De, the binding energy of H2, compared to 77% for the Hartree-Fock or molecular orbital wave function. This is not the only form of electron correlation in H2. In particular, angular correlation about the intemuclear axis is missing. But the type of non dynamic correlation present in wave function (4) ensures that molecular dissociation, however complex, is always correctly described. 

Each cell in the chart defines a model chemistry. The columns correspond to differcni theoretical methods and the rows to different basis sets. The level of correlation increases as you move to the right across any row, with the Hartree-Fock method jI the extreme left (including no correlation), and the Full Configuration Interaction method at the right (which fuUy accounts for electron correlation). In general, computational cost and accuracy increase as you move to the right as well. The relative costs of different model chemistries for various job types is discussed in... 

The periodic table can help us decide what type of ion an element forms and what charge to expect the ion to have. Fuller details will be given in Chapter 2, but we can begin to see the patterns. One major pattern is that metallic elements— those toward the left of the periodic table—typically form cations by electron loss. Nonmetallic elements—those toward the right of the table—typically form anions by gaining electrons. Thus, the alkali metals form cations, and the halogens form anions. 

Fig. 1 Sketches of break junction-type test beds for molecular transport. On the far left is a tunneling electron microscopy (TEM) image of the actual metallic structure in (mechanical) break junctions from the nanoelectronics group at University of Basel. The sketches in the middle (Reprinted by permission from Macmillan Publishers Ltd Nature Nanotechnology 4, 230-234 (2009), copyright 2009) and right (reproduced from Molecular Devices, A.M. Moore, D.L. Allara, and P.S. Weiss, in NNIN Nanotechnology Open Textbook (2007) with permission from the authors) show possible geometries for molecules between two gold electrodes, and (on the upper right) a molecule that has only one end attached across the junction...

Figure 11.2. Nanowire electronic and optical properties, (a) Schematic of an NW-FET used to characterize electrical transport properties of individual NWs. (inset) SEM image of an NW-FET two metal electrodes, which correspond to source and drain, are visible at the left and right sides of the image, (b) Current versus voltage for an n-type InP NW-FET. The numbers inside the plot indicate the corresponding gate voltages (Vg). The inset shows current versus Vg for Fsd of 0.1 V. (c) Real-color photoluminescence image of various NWs shows different color emissions, (d) Spectra of individual NW photoluminescence. All NW materials show a clean band-edge emission spectrum with narrow FWHM around 20nm. (See color insert.)...

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