Three-atom clusters

In Eq. (19) and (21) the atom-atom distances in two- and three-atom clusters are taken the same as in the original Af-atom cluster. 

In a three-atom clusters, the nonadditive effects are completely described by the 3-body forces. 

MnO is approximately 0.1 eV. The results of Nesbet s calculations are given in Table XIII. Although the agreement between observed and calculated N6el temperatures is quite good, it is important to realize that Uaa has been estimated only for a three-atom cluster, and considerable modification of this term can be anticipated for a solid where the clusters are located in the electrostatic Madelung field of the crystal. 

III. Collective Coordinates and Roles of a Metric Force Structural Isomerization Dynamics of Three-Atom Clusters... 

III. COLLECTIVE COORDINATES AND ROLES OF A METRIC FORCE STRUCTURAL ISOMERIZATION DYNAMICS OF THREE-ATOM CLUSTERS... 

It is again remarkable that all of the hyper-angles are locked in the isomerizing intervals similarly to the case of the three-atom cluster. Correspondence between the set of locked angles and the reaction channels is listed in Fig. 12. In our four-atom cluster composed of identical atoms, the angles at which the hyper-angles are locked are associated with the symmetry of... 

Os.3H2(CO)io behaves as an unsaturated cluster in that it is much more reactive than Os3(CO)i2. One way of looking at this is to say that, as a 46e cluster, it lacks 2e from the EAN count of 48e. It is often viewed as containing an Os=Os double bond because the EAN count for a system with four M—M bonds in a three-atom cluster is 46e. We would then regard an Os=Os double bond, like a C=C double bond, as being unsaturated. Structure 13.5 shows that there are two Os—H—Os bridges. 

While many spectroscopic studies have been published on dimers, the most extensive polymer studies have been with Ag, Na, and Cu clusters. As might be expected much of the interest in silver relates to the photographic process where it appears that a four-atom silver cluster on a silver halide surface leads to reduction by developer, whereas a three-atom cluster does not. The electron spin resonance (ESR) spectrum of sodium in argon confirms that the trimer is covalently bonded and not an equilateral triangle. Ultraviolet photoelectron spectroscopy (UPS) of Cu clusters indicates that the d band is separate from the s band, unlike in the bulk or in the Xa calculations mentioned earlier. 

For the interpretation of the measurements information on the structure of the clusters is very important. An ab initio calculation at one point of the total energy surface of a more than three-atom cluster including effects of correlation is a state-of-the-art task. A complete mapping of the surface is impossible. Therefore, we have used a model which is based on a reliable multi—center pair potential. Then the equilibrium geometries and total energy minima are determined by minimizing the intermolecular energy with respect to the molecular positions. To initiate a... 

FIGURE 1.14 Adsorption of additional hydrogen atoms at the three-atom cluster of Pd on Au(lll) surface. 

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