Search

The total electronic energy of a special class of finite clusters is calculated using the backfolding theorem and the properties of the trapezoidal quadrature. The resulting formula consists of a linear term, proportional to the size of the molecule and the remainder. It is found that the remainder is an irregular (or periodic) function of the cluster’s size. As a consequence the validity of the extrapolation of properties from small-size clusters to infinite solid state is questioned. [ABSTRACT FROM AUTHOR]

Structure, thermodynamics, and electronic properties are predicted for a new low energy phase of carbon which contains planar sheets equally occupied by sp2 and sp carbon atoms. The isolated planar sheets have the same planar symmetry as do the layers in graphite (p6m) and can be formally viewed as resulting from the replacement of one-third of the carbon–carbon bonds in graphite by –C 3/4 C– linkages. This material, called graphyne, is predicted to have a crystalline state formation energy of 12.4 kcal/mol carbon, which appears to be much lower than for any carbon phase which contains acetylenic groups as a major structural component. Based on the major structural reorganization required for graphitization and the observed high temperature stability of known model compounds, high temperature stability is predicted for graphyne. While graphyne will have similar mechanical properties as graphite, it is predicted to be a large bandgap semiconductor (Eg=1.2 eV) rather than a metal or semimetal. Based on this bandgap and the known behavior of related conjugated polymers having linear structures, interesting nonlinear optical properties (including a large third-order susceptibility) are expected. Property aspects are also predicted for other previously uninvestigated carbon phases which are structurally related to graphyne. Finally, structural features of alkali metal charge–transfer complexes of graphyne, which are expected to be metallic, and of related carbon phases are predicted. [ABSTRACT FROM AUTHOR]

The electronic and dynamic properties of all-trans polyacetylene have been calculated on the basis of oligomer calculations on H–(CH)10–H and H–(CH)22–H at the ab initio 6-31G level. The calculated ir and Raman intensities are in good agreement with the experimental relative intensities. [ABSTRACT FROM AUTHOR]

Errors introduced to the Hartree–Fock exchange term in the total electronic energy by a finite number of neighbors and a finite number of k-point approximations are discussed for a model metallic polymer. [ABSTRACT FROM AUTHOR]