Clusters double chains

The Pariser-Parr-Pople Hamiltonian for the description of the 7i-electrons in trans-polyacetylene is reparametrized using ab initio Coupled Cluster Doubles calculations based on a Restricted Hartree Fock reference on trans-butadiene. To avoid the spin contaminations inherent in Unrestricted Hartree Fock (UHF) type calculations on polymethine chains in the doublet state the Annihilated Unrestricted Hartree Fock (AUHF) model is applied in our PPP calculations (tPA (CH) , polyenes H-(CH)2N-H, polymethines H-(CH)2N+1-H). In geometry optimizations on polymethine chains it is shown that in contrast to results from Hiickel type models the width of neutral solitons is strongly... 

Figure 13. Pr IjRu - the double chains of condensed, Ru-centered clusters with iodine omitted Heft) a projection along the chains with iodine added (right). Dotted atoms differ by b/2 from those without.

Structure Before [...] 0 (isolated), 2x0 (dimer), 3x0 (trimer), 4x0 (tetramer), 5x0 (pentamer), 1 (chain), 2 x 1 (double chain), 2 (layer). Inside [...] O (octahedron), TP (trigonal prism), CTP (capped trigonal prism), BCHAP (bicapped hexagonal antiprism), C (cube), SAP (square antiprism), T (transition metal as endohedral atom), 6, 7, 8 (number of cluster atoms), 8, 12, X (number of ligands). After [...] C (cubic), T (tetragonal), O (orthorhombic), M (monoclinic)... 

Another, simple form of elemental carbon would be chains formed from carbon atoms. As a prototype model a single>stranded chain is most suitable. If branching were to be considered, all intermediate forms up to and including the diamond and graphite like clusters would be included. For non branched chains, the two variants to choose from are a system of alternating singly and triply bonded carbon atoms (poly-ynes), and a system with all double bonds (cumulenes). Cumulene structures are assumed to be the preferred ones for odd membered chains, whereas the even ones may have some poly-yne character. Recent studies on linear Cg show that a cumulene-like structure is preferred, both at the SCF level and when correlation is accounted for(50). 

The cluster condensation can be carried on the chains of octahedra sharing edges can be joined to double-strands and finally to layers of octahedra (Fig. 13.18). Every layer consists of metal atoms in two planes arranged in the same way as two adjacent layers of atoms in a closest-packing of spheres. This is simply a section from a metal structure. The X atoms occupy positions between the metal layers and act as insulating layers. Substances like ZrCl that have this structure have metallic properties in two dimensions. 

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