Potential contour map

J.J. Kaufman, P.C. Hariharan, F.L. Tobin, and C. Petrongolo, "Electrostatic Molecular Potential Contour Maps from Ab Initio Calculation", in Chemical Applications of Atomic and Molecular Electrostatic Potentials, P. Politzer and D.G. Truhlar (Eds.), Plenum, New York, 1981, pp. 335-380. 

Figure 1 shows a calculated two-dimensional electrostatic potential contour map of cytosine (1), in kcal/mol, in the plane of the ring. An extensive negative region is associated with N3 and Og, with three local minima. These V ,i are near N3 and Og, with values of - 85, - 70, and - 61 kcal/mol the... 

FIGURE 4.1 The potential contour maps for the molecules under discussion on their HOMO state. A higher density of contours indicates that the site is susceptible for electrophilic attack either for positive (green) or negative (in cyan) molecular electrostatic potential (Putz et al., 2010). 

Fig. 16 Equi-potential contour maps of (a) single crystal and (b) polycrystalline materials with highly resistive grain boundary pgb =100/9g, 5gb=0.02<7g). The changes of line and color indicate equi-potential lines. Potential drop between two neighboring lines is 1/20 of the applied voltage, according to [67].

The distinct roles of electrostatics in guiding different types of molecular interactions, can also be inferred fi om Figure 6, which shows iso-potential contour maps for the yeast cytochrome c and cytochrome c peroxidase and for the two identical monomers of bacterial desulforedoxin. Each pair of interacting molecules is shown oriented as in the... 

Apart from its simplicity, a major advantage of this technique is that large areas of concrete can be mapped with the use of mechanized devices. This approach is typically followed on civil engineering structures such as bridge decks, for which potential contour maps are produced to highlight problem areas. The potential measurements are usually performed with the reference electrode at the concrete surface and an electrical connection to the rebar. 

Figure 5.11 A polar representation of a potential contour map for the CIHI system, based on a semi-empirical LEP(S) computation. The potential energy contours (energy in kcal mol ) show the dependence of the potential on the approach angle y of the Cl, at fixed H—I separation. The dashed line shows the cone of approach within which the chlorine can abstract the H atom (adapted from C. A. Parr, J. C. Polanyi, and W. H. Wong, J. Chem. Phys. 58, 5 (1973)J.

The results of electrostatic potential calculations can be used to predict initial attack positions of protons (or other ions) during a reaction. You can use the Contour Plot dialog box to request a plot of the contour map of the electrostatic potential of a molecular system after you done a semi-empirical or ab initio calculation. By definition, the electrostatic potential is calculated using the following expression ... 

If we use a contour map to represent a three-dimensional surface, with each contour line representing constant potential energy, two vibrational coordinates can be illustrated. Figure 6.35 shows such a map for the linear molecule CO2. The coordinates used here are not normal coordinates but the two CO bond lengths rj and r2 shown in Figure 6.36(a). It is assumed that the molecule does not bend. 

The spirit of this kind of calculation is to give a rough and ready visualization to the potential reactivity of a molecule. For example, Figure 16.3 is a contour map for aspirin. These maps look much better in colour, and it is often possible to spot the route that an approaching charged reagent would take. 

The stable isotopic approach can be used to develop carbon budgets for individual sampling points in fields and can be used to develop contour maps (Fig. 8.7). These contour maps visualize the relationships between landscape position and potential carbon storage. In this budget, less new carbon was incorporated into summit shoulder... 

FIG. 8.6 Electrostatic potential maps in the region of one of the peptide links in iV-acetyl-a,/f-dehydrophenylalanine methylamide. (a) Observed, (b) From net charges fitted to the potential. Contours are at 0.05 eA 1 (1 eA) 1 = 332.1 kcal mol ). Zero and negative contours are dashed lines. Source Ghermani et al. (1993). 

However, the use of the new interaction potentials obtained from quantum mechanics (those used to compute the contour maps see discussion of the report of Dr. Williams) allows a rather accurate determination of how many molecules are placed in a given region (e.g., the cleft) and where each molecule is placed, with a precision far in excess of present-day X-ray resolution for proteins. Specifically, the count of molecules of water is accurate to 2 or 3% and the position is accurate to about 0.2 to 0.3 A. 

Fig. 5.1 Schematic energy band bending for (A) large particle, (B) small particle, and (C) metal-deposited particle. R, radius of the particle Lsc, space charge layer E(red/ox), redox level in solution E , Fermi level in semiconductor

Murrell and co-workers290 have reported MBS and DZ calculations on the nitro-methyl anion CH2N02 in its planar and pyramidal forms. The most stable form is planar, and is expected to protonate on the oxygen, whereas the pyramidal form would protonate on C. This conclusion was not obvious from charges alone, but was evident on examination of potential energy contour maps. 

---