First-principles study of ternary metal borocarbide compounds containing finite linear BC2 units

Electronic structures of the ternary metal borocarbide compounds Sc₂BC₂, Al₃BC₃ and Lu₃BC₃ containing linear BC₂ units are compared using density functional calculations. Results reveal a covalent bonding between the metallic matrix and the formally BC₂⁵⁻ nonmetal anions which is stronger for the aluminum compound than for the two others.     

Crystal graphs andq-analogues of weight multiplicities for the root systemA n

We give an expression of theq-analogues of the multiplicities of weights in irreducible in terms of the geometry of the crystal graph attached to corresponding . As an application, we describe multivariate polynomial analogues of the multiplicities of the zero weight, refining Kostant's generalized exponents.Partially supported by PRC Math-Info and EEC grant No. ERBCHRXCT930400.     

Crystal Structure,Photophysical Properties,and Theoretical Investigation of Extremely Distorted Pentacapped Trigonal-Prismatic Undecasilver Clusters

A new cluster family of the type [Ag₁₁(S){S₂P(OR)₂}₈]⁺ (R = Et, Pr, ⁱPr) has been synthesized and characterized as their hexafluorophosphate salts. These compounds are the first silver dithiophosph(in)ato complexes exhibiting photoluminescence at ambient temperature. Their unprecedented skeletal structure describes a very distorted pentacapped trigonal-prismatic polyhedron. Geometry optimizations by DFT calculations on the R = H model reproduce the same structural arrangement in the ground state. Its electronic structure exhibits a low-lying LUMO with a large Ag(5s/5p) character whereas the highest occupied levels have a major contribution from the ligand sulfur lone pairs. The above-mentioned orbitals are shown to be responsible for the optical absorption and emission properties of these compounds.     

Thermodynamic Correction for Salts in Variably Saturated Porous Media

Using thermodynamic principles, the general relationship describing the equilibrium vapor content in the gas phase above a saline liquid and across a curved liquid–gas interface is developed. Since high salt concentration affects the intensive and extensive liquid properties, it is also necessary to account for these effects in liquid water content/liquid water pressure relationship curves so that experimentally derived curves for pure water may be useful for elevated salt concentrations. The appropriate thermodynamic relationships are derived to describe the salt effects on liquid and vapor properties. The resulting equations are valid for salt concentrations between zero and saturation, and for any temperatures that nominally occur in nearsurface geologic materials.     

Symmetry lowering by cage doping in spherical superatoms: Evaluation of electronic and optical properties of 18-electron W@Au12Pt n (n = 0-4) superatomic clusters from relativistic DFT calculations

Attempts to expand the versatility of well defined clusters are a relevant issue in the design of building blocks for functional nanostructures. Here, we investigate the plausible formation of related structures from the emblematic highly symmetrical 18-e [W@Au₁₂] cluster. The calculated [W@Au₁₂Pt_n] series, with n = 0, 1, 2, 3, and 4, show cohesion energies, HOMO-LUMO gap, adiabatic electron affinities (AEAs) and adiabatic ionization potentials (AIPs), indicating a relative stability to the parent cluster [W@Au₁₂] experimentally characterized, where clusters with n = 1 and n = 4 are suggested as the most stable with respect to oxidation. The resulting symmetry lowering away from the high icosahedral symmetry upon adding Pt atoms induces a sizable splitting of the frontiers shells, which in turn effectively modify the properties of the calculated clusters, as observed from calculated optical properties. The estimated absorption spectra show an interesting broadening effect of the absorption peaks, which appears as a useful approach for further design of broad black absorbers, which are able to absorb light in a wider range, with potential capabilities to enhance the efficiency of thin film solar cells and photocatalysis processes, among other applications.     

Extended three-dimensional digital image correlation (X3D-DIC)

A correlation algorithm is proposed to measure full three-dimensional displacement fields in a three-dimensional domain. The chosen kinematic basis for this measurement is based on continuous finite-element shape functions. It is furthermore proposed to account for the presence of strong discontinuities, similarly to extended finite element schemes, with a suited enrichment of the kinematics with discontinuities supported by a (crack) surface. An optimization of the surface geometry is proposed based on correlation residuals. The procedure is applied to analyze one loading cycle of a fatigue-cracked nodular graphite cast iron sample by using computed tomography pictures. Subvoxel crack openings are revealed and measured. To cite this article: J. Réthoré et al., C. R. Mecanique 336 (2008).     

Theoretical Analysis of the Mackay Icosahedral Cluster Pd55(PiPr3)12(μ3-CO)20: An Open-Shell 20-Electron Superatom

The electronic structure of the spherical Mackay icosahedral nanosized cluster Pd₅₅(PiPr₃)₁₂(μ₃-CO)₂₀ is analyzed by using DFT calculations. Results reveal that it can be considered as a regular superatom with a “magic” electron count of 20, characterized by a 1S² 1P⁶ 1D¹⁰ 2S² jellium configuration. Its open shell nature is associated with partial occupation of non-jellium, 4d-type, levels located on the interior of the Pd₅₅ kernel. This shows that the superatom model can be used to rationalize the bonding and stability of spherical ligated group 10 clusters, despite their apparent 0-electron count.