Bond charge density

Figure 1. The charge-density difference (bonding charge density) between NiaX and the superposition of neutral Ni and X atomic charge densities on the (001) planes for (a) X = A1 and (b) X = Si. The solid (dotted) contours denote contours of increased (decreased) density as atoms are brought together to form the NiaX (X = Al, Si) crystal. Contours start from 4.0 X 10 e/(a.u.) cind increase successively by a factor of root 2.

A set of simple physical and chemical principles can be used to understand and predict the surface reconstruction or faceting, which occurs on oxide surfaces.8,9 These include (1) autocompensation of stable surfaces, (2) rehybridization of the dangling bond charge density, (3) formation of an insulating surface, (4) conservation of near-neighbor bond lengths (which minimize the formation of surface strain fields), and (5) surface kinetic factors. We shall briefly discuss all of these factors governing the surface reconstruction of metal oxide. 

Once a particular surface structure has been determined to be stable (i.e., autocompensated), the primary factor determining the nature of the surface reconstruction is the energy that can be gained by rehybridizing the surface dangling bond charge density in response to the reduced coordination at the surface. As a consequence, a charge transfer between the atoms at the surface takes place and this results in the formation of new bonds between surface atoms adsorbed to the surface (also known as adatoms). The formation of new bonds on the surface leads to different chemical and physical properties at the surface.11... 

Drozdova O, Yakushi K, Yamamoto K, Ota A, Yamochi H, Saito G, Tashiro H, Tanner DB (2004) Optical characterization of 2kp bond-charge-density wave in quasi-one-dimensional 3/4-filled (ED0-TTF)2X (X = PFg and AsFg). Phys Rev B70 075107-1/8... 

Bridged metal-metal bonds, charge density studies, 1, 592... 

Other molecular descriptors derived from the charge density matrix are the average atom charge density Pi and the average bond charge density P2, defined as ... 

Fig. 15. Total valence electron charge density for the Si(111)-(lxl) surface. A (110) plane is shown with the top of the diagram representing the semiconductor surface. The cores are shown as shaded discs, and heavy lines represent bonds. Charge density contours are normalized to e/fi where is the bulk unit cell. (from Ref. 53) ... 

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