Carbon-atom clusters properties

In 1985 Car and Parrinello invented a method [111-113] in which molecular dynamics (MD) methods are combined with first-principles computations such that the interatomic forces due to the electronic degrees of freedom are computed by density functional theory [114-116] and the statistical properties by the MD method. This method and related ab initio simulations have been successfully applied to carbon [117], silicon [118-120], copper [121], surface reconstruction [122-128], atomic clusters [129-133], molecular crystals [134], the epitaxial growth of metals [135-140], and many other systems for a review see Ref. 113. 

The structure of a-C H films may be thus pictured as sp--carbon atoms in condensed aromatic clusters, dispersed in an sp- -rich matrix, which confers to the network its characteristic rigidity. This situation can also be regarded as a random covalent network in which the sp" clusters of a defined size take part in the structure as an individual composed atom with its corresponding coordination number [17]. Such kinds of models have been successfully used to describe the dependence of a-C H film mechanical properties on composition, hybridization, and sp" clustering [23]. 

On the basis of the information described above, some general observations may be made about carbidocarbonyl clusters. The source of the carbon atom, its structural requirements, and its chemical properties are all of interest, as is the effect that it has on the chemistry of the cluster as a whole. 

A common instance of the approximate invariance is the occurrence of chromophores, i.e., small atomic clusters having identifiable spectral properties.21 24 The empirical theory of organic dyes contains many such examples, e.g., the carbonyl group R2CO, the nitro group RN02 or, for that matter, the six carbon... 

The MO procedure has recently been applied to adsorbates on a wide variety of substrates. We shall be concerned primarily with the effect of substrate on electronic properties of adsorbed atoms. Clusters of Ag and Pd on nonionic (carbon) substrate and ionic (AgBr) substrate have been examined for this effect. In addition, properties of small atomic number adatoms on graphite were calculated in an extensive study, which is reviewed here. Metal substrates have also been treated by MO procedure. 

Carbon atoms crystallize in several forms. Graphite and diamond are well known carbon polymorphs. Fullerenes, which were discovered in the 1980 s, have also been well characterized. Carbon materials show a variety of different physical and chemical properties. Because of this the electronic structure of carbon materials has been investigated using a number of different experimental techniques, for example, XPS, UPS and XANES. Theoretical studies of carbon materials have been also performed. However, experimentally observed spectra are not always consistent with theoretical predictions. Recently, in order to understand the various kinds of observed electronic spectra, DV-Xa calculations have been performed on a small cluster model. [1] In the present paper, we report results of DV-Xa calculations performed on the carbon materials graphite, alkali graphite intercalation compounds (GIC), fullerene, and fluorinated fullerenes. 

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