Metal surface configuration, methods

The most popular method is molecular dynamics. A suitable geometry is shown in Fig. 17.7. A certain number of water molecules are enclosed in a cubic or rectangular box. Two opposite sides of the box, at x = 0 and L, represent two metal surfaces (electrodes). Cyclic boundary conditions are imposed in the y and z directions, that is, a particle that leaves the box at y = L enters again at y = 0, and similarly for the z direction. One starts with a suitable configuration, and... 

The structure and dynamics of clean metal surfaces are also of importance for understanding surface reactivity. For example, it is widely held that reactions at steps and defects play major roles in catalytic activity. Unfortunately a lack of periodicity in these configurations makes calculations of energetics and structure difficult. When there are many possible structures, or if one is interested in dynamics, first-principle electronic structure calculations are often too time consuming to be practical. The embedded-atom method (EAM) discussed above has made realistic empirical calculations possible, and so estimates of surface structures can now be routinely made. 

The central problem of the atomic theory of metal surfaces is the proper determination of the surface energy of ideally flat and atomically smooth faces of a simple metal crystal. The methods of quantum mechanics permit the computation of energies with much less effort than is needed for a description in terms of correct wave functions and, of course, the construction of a successful theory of surface energy must touch on most other aspects of the atomic nature of surfaces, such as the potential in the surface region and its associated double layer, or the atomic arrangement and the change in electronic configuration in the surface. 

The application of the ATR method in Raman spectroscopy provides a unique way to study essentially mirrorlike polished metals, in particular single crystalline surfaces. The ATR method is used to excite surface plasmon polaritons (SPPs) effectively at the smooth metal surface, to improve the sensitivity in Raman spectroscopy by electromagnetic field enhancement [19]. The enhancement of the ATR configuration, as shown in Figs. 8(d and e), with respect to the normal external reflection geometry spans one to three orders, depending on the electrodes and their crystallographic orientations. 

FIGURE 2.13 (a) Initial solvent-metal particle configuration, (b) electronic structure energies for dissolution/bond breaking of a copper atom in proximity to a (111) copper surface, and (c) charges determined by the method of Bader for the copper adatom being dragged away from the (111) copper surface. Reproduced with permission from Taylor [172]. Elsevier. 

Full dimensional quantum dynamics calculations on polyatomic molecules will hopefully lead to a deeper understanding on molecule/surface interactions mechanisms, as the six-dimensional quantum dynamics calculations have already done for H2/metal surfaces. These kind of simulations are required to describe accurately processes involving the breaking of a X-R bond, beyond dissociation of CH4 on H and CH3. A description along the lines of the MCTDH (multi-configurational time-dependent Hartree) method would be worth exploring. For these polyatomic molecules, a better description of the molecule-lattice coupling is also desirable. 

The main focus of the project was the elucidation of particle-stabilizer-solvent interactions as a function of the binding strength, the chain length, the concentration of the stabilizers, the polarity of the solvents, and the surface configuration as well as the size and morphology of the metal oxide nanoparticles. Therefore, to characterize the stabilization kinetics, a number of analytical methods, such as thermogravimetric analysis, isothermal titration calorimetry, and spectroscopic methods, were combined. 

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