Computed adsorption energy

Several numerical procedures for EADF evaluation have also been proposed. Morrison and Ross [19] developed the so-called CAEDMON (Computed Adsorption Energy Distribution in the Monolayer) method. Adamson and Ling [20] proposed an iterative approximation that needs no a priori assumptions. Later, House and Jaycock [21] improved that method and proposed the so-called HILDA (Heterogeneity Investigation at Loughborough by a Distribution Analysis) algorithm. Stanley et al. [22,23] presented two regularization methods as well as the method of expectation maximalization. 

We see that the terms that differ for various adlayer structures do not depend on the systematic error a. These terms are also the ones that contain the lateral interactions. This means that the systematic error does not affect the lateral interactions. They depend only on the smaller random errors p . This means that lateral interactions can be determined better than one might suppose having some idea of the accuracy with which one can compute adsorption energies with DFT. The systematic errors cause only a shift in l s-... 

Blaszkowski et al. (221) demonstrated that the methanol molecule is capable of adsorbing in a physisorbed state in two different modes, the end-on mode, shown in the first part of Fig. 12, and a side-on mode, shown in Fig. 13a. In this side-on mode, a C-H bond of the methanol CH3 group is directed toward the zeolitic basic oxygen site, while the acidic zeolite proton retains its strong hydrogen bond with the methanol oxygen. The authors used TST (4) to determine the equilibrium constants for the two modes of adsorption from the computed adsorption energies. The equilibrium constant for the side-on mode is a factor of 106 smaller than that for the end-on mode at 300 K. Thus, nearly all methanol molecules adsorb in an end-on manner, but the dehydration reaction necessitates conversion to the side-on form. 

Ross, S. and Morrison I.D. (1975). Computed adsorptive-energy distribution in the monolayer (CAEDMON). Surf. ScL, 52, 103-19. 

Table 3. Computed adsorption energies at terrace sites ...

In Table 10.1 [3], a comparison is made of computed adsorption energies of C atoms attached at difierent sites on dilferent surfaces of Ru. The energies have been ranked according to the coordination number of the C atom, which is the first number in the fourth column of Table 10.1. The number within brackets in... 

This is highlighted by Tables 10.2 and 10.3 that show DFT-computed adsorption energies of C and O atoms, respectively, on the dense surfaces of the group VIII and IB metals of the periodic system. The structures of the surfaces considered are the same as well as the coordination of the adsorbed atoms. 

FIGURE 2.7 Thermodynamic cycles are used to combine computed adsorption energies for molecular/ionic species fiom first-principles calculations, with thermodynamic data available in the hterature, to determine the overall fi-ee energy of adsorption of solution-phase species to the mild steel surface. Cycles are shown for Equations (a) 2.13, (b) 2.16, (c) 2.15, and (d) 2.14. Reproduced with permission from Taylor [136]. National Association of Corrosion Engineers. 

Apart from the original method mentioned above, Morrison and eo-workers [143,144] formulated a new iterative teehnique ealled CAEDMON (Computed Adsorption Energy Distribution in the Monolayer) for the evaluation of the energy distribution from adsorption data without any a priori assumption about the shape of this function. In this case, the local adsorption is calculated numerically from the two-dimensional virial equation. The problem is to find a discrete distribution function that gives the best agreement between the experimental data and calculated isotherms. In this order, the optimization procedure devised for the solution of non-negative constrained least-squares problems is used [145]. The CAEDMON algorithm was applied to evaluate x(fi) for several adsorption systems [137,140,146,147]. Wesson et al. [147] used this procedure to estimate the specific surface area of adsorbents. 

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