[en] The electronic structure of a one-dimensional binary alloy A_1/τB_1/τ² (τ = golden mean) with A and b atoms distributed in a Fibonacci sequence is studied using a tight binding model in which the variation in both the diagonal and off-diagonal terms is treated simultaneously. In contrast to the previous 'diagonal' and the 'off-diagonal' models, for the 'mixed' model we find an extended state. Also in the limiting case of the 'off-diagonal' model, the state corresponding to E=0 is an extended state. (author). 6 refs, 2 figs

[en] From studies on some clusters of metals and semiconductors, there appear some similarities in the structure of clusters with a given number of atoms and having the number of valence electrons corresponding to a shell closing. Here we present results of the atomic and electronic structure of a few other clusters with 20 and 40 valence electrons, namely Sb₄, Sn₅ and Sb₈ using the density functional molecular dynamics method. We suggest that the similarities in the structure and deviation from them may help to understand bonding characteristics in clusters and its evolution to bulk behaviour. Our results on Sb₈ cluster are preliminary but indicate that above room temperature its structure is two weakly interacting tetrahedra which is in general agreement with the observation of predominently antimony tetramers at T > 300 K. (author). 16 refs, 2 figs

[en] The electronic and atomic structure of Sb₄ and Sb₈ clusters is studied using the ab-initio molecular dynamics method in the local density approximation. While for Sb₄ we obtain a regular tetrahedron to be about 2.0 eV lower in energy than a bent rhombus, for Sb₈ two structures, (1) two weakly interaction tetrahedra and (2) a bent rhombus interacting with a stretched tetrahedron, obtained from the simulated annealing lie only within about 0.1 eV indicating the importance of the bent rhombus structure for larger clusters. As compared to two isolated tetrahedra, the binding energy of Sb₈ is about 0.5 eV. Our results are thus in excellent agreement with the experimental data which show predominantly the abundance of tetramers above room temperature. (author). 18 refs, 5 figs, 1 tab

[en] The structure of clusters Ti₈ C₁₂ and Ti₂₄ C₃₆ is briefly discussed. 8 refs, 1 fig

[en] With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

[en] We review here the recent progress made in the understanding of the electronic and atomic structure of small clusters of s-p bonded materials using the density functional molecular dynamics technique within the local density approximation. Starting with a brief description of the method, results are presented for alkali metal clusters, clusters of divalent metals such as Mg and Be which show a transition from van der Waals or weak chemical bonding to metallic behaviour as the cluster size grows and clusters of Al, Sn and Sb. In the case of semiconductors, we discuss results for Si, Ge and GaAs clusters. Clusters of other materials such as P, C, S, and Se are also briefly discussed. From these and other available results we suggest the possibility of unique structures for the magic clusters. (author). 69 refs, 7 figs, 1 tab

[en] A numerical analysis procedure using the boundary-integral equation method is presented for the solution of problems of time-dependent inelastic deformation in planar metallic bodies. The formulation allows the use of both classical creep theories in the absence of time-independent plasticity as well as newer theories of inelastic deformation using state variables. Numerical results are presented for plane stress problems using either the power law equations of creep or the state variable theory due to Hart. Comparison of BIE and analytical methods for simple problems shows good agreement. Other features of the numerical solutions of more complicated problems are discussed in the paper

[en] Several newer constitutive relations have recently been proposed for describing the mechanical behavior of metals and alloys under elevated temperature creep conditions. A salient feature of the mathematical structure of many of these relations is that they typically express the nonelastic strain rates as functions of the current values of stress, temperature, and some other suitably defined state variables. A computational scheme is presented for the inelastic analysis of metallic structures subjected to both mechanical and thermal loadings and obeying constitutive relations of the type described above. Several numerical examples for the creep of thick-walled spheres, cylinders, and rotating discs in the presence of thermal gradients are presented. The particular constitutive relations used in these calculations are due to Hart. The proposed computational scheme is found to be very efficient from the view point of both computational time and effort. The effects of previous cold work on the stress redistribution and creep of these structural elements are discussed

[en] The electronic structure and relative stability of icosahedral Al₁₂TM superatoms in Al-transition-metal (TM) alloys have been studied using the density functional theory within the local spin density approximation. Our calculations predict large binding energies for superatoms with TM atom in the middle of a d-series in agreement with the occurrence of Al₁₂W phase in these alloys and provide an insight into the understanding of the stability of Al-TM quasicrystal. (author). 16 refs, 2 figs, 2 tabs

[en] We present a tight-binding model for the electronic structure of C₆₀ using four (1s and 3p) orbitals per carbon atom. The model has been developed by fitting the tight-binding parameters to the ab-initio pseudopotential calculation of Troullier and Martins (Phys. Rev. B46, 1754 (1992)) in the face-centered cubic (Fm3-bar) phase. Following this, calculations of the energy bands and the density of electronic states have been carried out as a function of the lattice constant. Good agreement has been obtained with the observed lattice-constant dependence of T_c using McMillan's formula. Furthermore, calculations of the electronic structure are presented in the simple cubic (Pa3-bar) phase. (author). 43 refs, 3 figs, 1 tab