Structure decahedral

Cleveland, C.L., Landman, U., Schaaff, T.G., Shafigullin, M.N., Stephens, P.W. and Whetten, R.L. (1997) Structural Evolution of Smaller Gold Nanocrystals The Truncated Decahedral Motif Physical Review Letters, 79, 1873-1876. 

Initiation of growth may also proceed by formation of metastable structures when nucleation is inhibited. Multiply twinned structures have been observed for a number of metals. Their presence indicates an icosohedral or decahedral precursor cluster which has decomposed to a multiply twinned crystal at a critical size [117, 118], Another example of metastable intermediate structures was reported by Dietterle et al. 

A cluster framework such as that seen in U has also been observed for its heavier homologues (14). Apparently, the latter topology is the result of a close packing of anionic pnictide moieties with alkali metal ions that maximizes ionic interactions. The topology of the rhombodo-decahedral Li6PeSi2 framework in U has been simply described as a Pe octahedron representing the anionic partial structure, of which the triangular faces are capped by two p.3-RSi moieties and six /t3-Li ions as counterion partial structure (Fig. 3). 

A special group of particles that are often produced are the icosahedral (I5) and decahedral (D5) structures shown in Fig. 9. These particles have a fivefold symetry axis which is forbidden for infinite crystals. Yang (1 0) has described these particles using a non-Fcc model. The particles are composed by five (D5) and twenty (I5) tetrahedral units in twin relationship. However the units have a non-Fcc structure. The decahedral is composed by body-centered orthorhombic units and the icosahedral by rhombohedral... 

FJ clusters (in FJ units, or as a model for specified rare-gas atom clusters) continue to be used as a benchmark system for verification and tuning in method development. With the work of Romero et al. [52], there are now proposed global minimum structures and energies available on the internet [53], up to n=309. This considerably extends the Cambridge cluster database [54], but the main body of data comes from EA work that used the known FJ lattices (icosahedral, decahedral, and face-centered cubic) as the input. This is obviously dangerous,... 

For carbon, it is of course also tempting to study clusters of clusters, namely aggregation of C60 fullerenes [67-69]. This is not really a molecular cluster application since the inner structure of the fullerene, leading to dependence of the particle interaction on relative particle orientation, is largely or completely ignored. The Pacheco-Ramalho empirical potential is used frequently, and fairly large clusters up to n=80 are studied. There appears to be agreement that small fullerene clusters are icosahedral in this model. In contrast to LJ clusters, however, the transition to decahedral clusters appears to occur as early as at n=17 the three-body term of the potential is found to be responsible for this [67]. 

Cleveland CL, Landman U, Schaaff TG, ShafigaUin MN, Stephens PW, Whetten RL (1997) Structural evolution of smaller gold nanocrystals the truncated decahedral motif. Phys Rev Lett 79 1873... 

As recalled in the Introduction, clusters with anomalous external shajjes, icosahedral or decahedral, have been found frequently in deposits from fee metals. Therefore, the stability and the structure have been the main questions asked about these metallic particles. Several ideas develojjed in the preceding sections may help clarify both points. 

But also the other coinage elements have been studied intensively, although here the results depend much less sensitively on the approximate or exact description that is used for the interatomic interactions. Among those is Ag. Clusters of Ag were studied by Baletto et alP who used a molecular-dynamics method to determine the stable structures for selected cluster sizes with up to almost 600 atoms. In order to identify the crystal-growth modes, they used the common-neighbour analysis (Section 3.5) in distinguishing between icosahe-dral, decahedral, and fcc-like motifs. From their analysis they were also able to propose a cluster-growth mechanism. 

Brown and co-workers reported the formation of completely condensed cubic cage-structured octahedral octaphenylsilsesquioxane (Ph-Tg). The other typical cage is decahedral decasilsesquioxane, Tm-... 

The crystal structures among LGS, PCS and NGS differ mostly in shape of each site. In particular, the change of the A-site is remarkable. The decahedral A-site expands with the increase of ionic radius of rare earth (R) that occupies the A-site. The A-site expands greatly in [100] directions compared to the expansion in [120], which is perpendicular to [100], with the increase of the ionic radius of R. 

Tg is often called cubic. Brown reported the formation of cubic cage-structured octaphenyloctasilsesquioxaneCPhgTg) [3-5]. The other typical cages are hexahedral hexasilsesquioxane, Te, decahedral decasilsesquioxane, Tio, and dodecahedral do-decasilsesquioxane T12. 

Fig. 2 The structure types for Morse clusters with N atoms as a function of the potential-range parameter po and of N. The structures are split into close-packed, decahedral, disordered, and three types of icosahedral ones (labeled 21, 31, and 41, respectively, depending on whether it is based on the icosahedron with 13, 55, or 147 atoms). Reproduced with permission of American...

Fig. 5 The number of times a given structure is found in 40 different simulations as a function of cluster size N for Lennard-Jones clusters. Irreg, DH, MIC, s-IC, r-PIC, and d-Cryst mark irregular, decahedral, multishell icosahedral, surface-centered icosahedral, regular polyicosahedral, and defective crystalline clusters, respectively. Reproduced with permission of American Physical Society from ref 15.

Fig. 6 Different structures (marked a-d) for clusters with N = 700 atoms. The structural motifs have been characterized according to similarity with (top row) face-centered cubic, (second row) hexagonal close-packing, (third row) icosahedral, and (bottom row) decahedral structures. The dark-shaded parts of the clusters mark those regions where the structural motif in quest is found. Reproduced with permission of American Physical Society from ref. 15.

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