Overlapping potential

Gay J G and Berne B J 1981 Modification of the overlap potential to mimic a linear site-site potential J. Chem. Phys. 74 3316-19... 

Gay J G and B J Berne 1981. Modification of the Overlap Potential to Mimic a Linear Site-Site Potential. Journal of Chemical Physics 74 3316-3319. 

The channels in zeoHtes are only a few molecular diameters in size, and overlapping potential fields from opposite walls result in a flat adsorption isotherm, which is characterized by a long horizontal section as the relative pressure approaches unity (Fig. 6). The adsorption isotherms do not exhibit hysteresis as do those in many other microporous adsorbents. Adsorption and desorption are reversible, and the contour of the desorption isotherm foUows that of adsorption. 

J. G. Gay, B. J. Berne. Modification of the overlap potential to mimick a linear site-site potential. J Chem Phys 74 3316-3319, 1981. 

Type I isotherms are encountered when adsorption is limited to, at most, only a few molecular layers. This condition is encountered in chemisorption where the asymptotic approach to a limiting quantity indicates that all of the surface sites are occupied. In the case of physical adsorption, type I isotherms are encountered with microporous powders whose pore size does not exceed a few adsorbate molecular diameters. A gas molecule, when inside pores of these small dimensions, encounters the overlapping potential from the pore walls which enhances the quantity adsorbed at low relative pressures. At higher pressures the pores are filled by adsorbed or condensed adsorbate leading to the plateau, indicating little or no additional adsorption after the micropores have been filled. Physical adsorption that produces the type I isotherm indicates that the pores are microporous and that the exposed surface resides almost exclusively within the micropores, which once filled with adsorbate, leave little or no external surface for additional adsorption. 

Instances have been found in which BET plots were noted to be linear to relative pressures as high as 0.5, and in other cases the linear range is found only below relative pressures of 0.1.The extent to which these deviations from the usual range of linearity reflect unusual surface properties is difficult to ascertain. For example, micropores exhibit unusually high adsorption potentials due to the overlapping potential from the walls of the micropore. Under these enhanced conditions condensation can occur within the pores at relative pressures less than 0.1, and linear BET plots are found at even lower relative pressures. 

In a pore the overlapping potentials of the walls more readily overcome the translational energy of an adsorbate molecule so that condensation will occur at a lower pressure in a pore than that normally required on an open or plane surface. Thus, as the relative pressure is increased, condensation will occur first in pores of smaller radii and will progress into the larger pores until, at a relative pressure of unity, condensation will occur on those surfaces where the radius of curvature is essentially infinite. Conversely, as the relative pressure is decreased, evaporation will occur progressively out of pores with decreasing radii. 

Equation (9.7) is applicable to micropores rather than larger pores because the overlapping potential from the walls of pores only slightly larger than an adsorbate molecule will considerably enhance the adsorption potential. 

Calculated Values of the Electron Overlap Potentials at Metal/Solution Interfaces... 

J. O M. Bockris and M. A. Habib, The Electron Overlap Potential at Metal-Solution Interfaces, / Electroanal. Cheni. 68 367 (1976). 

Onitsuka T, Ninomiya H, Sato E, Yamamoto T, Tashiro N. 2000. The effect of interstimulus intervals and between-block rests on the auditory evoked potential and magnetic field is the auditory P50 in humans an overlapping potential Clin Neurophysiol 111 237-245. 

Figure 12. The numbers of overlapping potential 4-point pharmacophores for ligands with those calculated for the active sites of thrombin, factor Xa, and trypsin on the basis of complementary site-points the arrow points to the enzyme for which the ligand shows biological activity).

Surface physics of electron overlap potential very near surface of metal Physical chemistry of surface reactions Metallurgy, e.g., sputtered film formatiort on surface ... 

An illustration is given in fig. 3.16 for a spherical cavity. As with convex double layers, the potential drops more rapidly (inweird from the surface) with distance in 10 M than in 10" M solution in the latter case the decrease is so weak that in the centre a substantial overlap potential remains. Similar results have been obtained by others 2-3 emphasizing other aspects, such as the ton uptake (or exclusion), the Gibbs energy and the disjoining pressure. This information underlies the thermodynamics of vesicle and micro-emulsion formation. 

For large pores (mesopores and macropores), the contribution of solid-fluid potential is negligible (the first term in the RHS) and the above equation is reduced to the modified Kelvin equation. On the other hand, for small pores of molecular dimension the overlapping of potentials exerted by the two opposite walls is such that the overlapped potential outweighs the surface tension effect... 

The channals in zeolites are only a few molecular diameters in size, and overlapping potential fields... 

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