Clusters dynamic properties

Chemical bonding and dynamic properties of Au clusters are obtained by recoilless y-ray spectroscopy and- P NMR investigations - . ... 

Calvo, F. Neirotti, J.P. Freeman, D.L. Doll, J.D., Phase changes in 38-atom Lennard-Jones clusters. II. A parallel tempering study of equilibrium and dynamic properties in the molecular dynamics and microcanonical ensembles, J. Chem. Phys. 2000, 112, 10350-10357... 

Besides the applications of the electrophilicity index mentioned in the review article [40], following recent applications and developments have been observed, including relationship between basicity and nucleophilicity [64], 3D-quantitative structure activity analysis [65], Quantitative Structure-Toxicity Relationship (QSTR) [66], redox potential [67,68], Woodward-Hoffmann rules [69], Michael-type reactions [70], Sn2 reactions [71], multiphilic descriptions [72], etc. Molecular systems include silylenes [73], heterocyclohexanones [74], pyrido-di-indoles [65], bipyridine [75], aromatic and heterocyclic sulfonamides [76], substituted nitrenes and phosphi-nidenes [77], first-row transition metal ions [67], triruthenium ring core structures [78], benzhydryl derivatives [79], multivalent superatoms [80], nitrobenzodifuroxan [70], dialkylpyridinium ions [81], dioxins [82], arsenosugars and thioarsenicals [83], dynamic properties of clusters and nanostructures [84], porphyrin compounds [85-87], and so on. 

Classical relaxors [22,23] are perovskite soUd solutions like PbMgi/3Nb2/303 (PMN), which exhibit both site and charge disorder resulting in random fields in addition to random bonds. In contrast to dipolar glasses where the elementary dipole moments exist on the atomic scale, the relaxor state is characterized by the presence of polar clusters of nanometric size. The dynamical properties of relaxor ferroelectrics are determined by the presence of these polar nanoclusters [24]. PMN remains cubic to the lowest temperatures measured. One expects that the disorder -type dynamics found in the cubic phase of BaTiOs, characterized by two timescales, is somehow translated into the... 

The dynamic properties of paramagnetic clusters are difficult to assess experimentally. The EPR spectra of the paramagetic ions are not particularly informative... 

The dynamic properties of these two complexes are perhaps the most surprising and interesting of the transition metal Zintl ion complexes. The clusters have markedly different structures but are both prolate in nature with several different Sn environments. The tin atoms at opposite ends of both structures are separated by nearly 9 A, but all 17 atoms are in fast intramolecular exchange on the NMR time scale. 

It has been shown that a variety of substituents can be attached to the outside of the group 14 Zintl ion clusters in exo positions (i.e., not vertex or interstitial positions) [70,73-78]. A variety of alkyl, aryl, and main group moieties have been attached to Ge9 and Sn9 clusters. The structures of these clusters are similar to some organos-tannane clusters prepared via different synthetic routes. This burgeoning class of compounds is rapidly developing however, little is known about the effect of the exo-substituents on the dynamic properties of the clusters. Only the RSng ions, where R = i-Pr, t-Bu, and SnCys, Sn- -Bu3, have been studied in detail [70]. 

A very large number of theoretical studies have been performed on MgO and AI2O3. Only some of the early studies and some of the most recent will be described here, in order to give some idea of the extent of progress over the past two decades. Important advances have recently been made in the application of ionic models to such materials as well as in band-theory studies and embedded-cluster studies. After reviewing the early work, contemporary studies of structure, stability, phase relations, and dynamic properties will be described, followed by recent studies of spectral properties and characteristics of the electron-density distribution for each of these materials. Attention is then turned to Si02, the silica polymorphs, and various compounds and clusters that may be used to model tetrahedrally coordinated Si in silica and the silicates. 

As a final part of this chapter, we shall briefly discuss the intramolecular ET processes in relatively large aromatic molecules. This is a supplement to Chapter 3 in this Part, in which twisted intramolecular charge-transfer (TICT) phenomena were described for isolated donor acceptor molecules and their clusters. Here we present the charge-transfer dynamics in some selected anthryl derivatives in which the donor and acceptor parts are linked directly or by alkyl chains, and also microscopic solvation effects on the dynamic properties in their clusters, which were not discussed in the earlier chapter. The emphasis resides on a detailed description of the torsional motions and the solvation structure, which are strongly correlated with the intramolecular charge transfer in these systems. 

Our calculations show that the smallest size quantum model (MOD-A) does not provide an adequate description for neither structural, nor electronic or dynamical properties. In contrast, a cluster model of the size of MOD-B is able to reproduce the structural properties of the real system quite accurately and provides also a qualitative description of the electronic and dynamic features ... 

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