Showing papers in "Journal of Computer-aided Materials Design in 1994"
TL;DR: Multi-attribute utility analysis has emerged as a powerful tool for materials selection and evaluation and extends beyond the problem of materials selection into the more speculative areas of materials competitiveness and market demand in cases involving new, unproven technologies.
Abstract: Multi-attribute utility analysis (MAUA) has emerged as a powerful tool for materials selection and evaluation. An operations research technique, MAUA has been used in a wide range of engineering areas, of which materials science and engineering is one of the more recent. Utility analysis affords a rational method of materials selection which avoids many of the fundamental logical difficulties of many widely used alternative approaches. However, MAUA has traditionally been used in materials selection problems only, in which there is certainty regarding the attribute levels of the alternatives. For many new technologies this is not the case. Another operations research technique, subjective probability assessment (SPA), can be used to address this issue. SPA makes it possible to measure a probabilistic distribution describing the confidence of the decision maker in the levels of attributes for which there is a high degree of uncertainty. These probability distributions can be used in conjunction with MAUA to provide a consistent framework for making materials selection decisions. Furthermore, the use of these techniques extends beyond the problem of materials selection into the more speculative areas of materials competitiveness and market demand in cases involving new, unproven technologies.
48 citations
TL;DR: In this paper, experimentally unknown crystal structures of heteroatom-containing molecules are predicted for the first time at the level of atomic coordinates, and the first prediction deals with a novel racemic modification of cyclo-di-alanyl.
Abstract: Recent progress in solving the crystal packing problem from molecular information only for organic molecules containing heteroatoms leads to good agreement between ‘predicted’ and experimentally determined crystal structures. Until now these complex computations have not been used for a ‘true’ prediction prior to experiment. In this contribution experimentally unknown crystal structures of heteroatom-containing molecules are predicted for the first time at the level of atomic coordinates. The examples are easily verifiable; the first prediction deals with a novel racemic modification of cyclo-di-alanyl, of which only the enantiomerically pure cyclo-l-alanyl-l-alanyl crystal structure is known, and the second prediction with a new crystal modification of cyclo-bis(dehydro-alanyl).
34 citations
TL;DR: In this article, the authors examined theoretically the stress distribution around fiber breaks in a unidirectional reinforced metal matrix composite, subjected to axial loading when plastic yielding of the matrix is allowed to occur.
Abstract: This paper examines theoretically the stress distribution around fiber breaks in a unidirectional reinforced metal matrix composite, subjected to axial loading when plastic yielding of the matrix is allowed to occur. The composites considered have a ductile interphase, bonding the matrix to the fiber. The likelihood of failure of a fiber adjacent to the existing broken fiber is considered. Detailed and systematic results are given for composites with a wide range of fiber volume fractions, Young's modulus of the fibers and the matrix, interphase properties and Weibull modulus for the strength of the fibers. The objective is the optimization of these material and geometric variables to ensure global load sharing among the fibers in the longitudinal direction, which will give the composite good longitudinal strength. Calculations are carried out for transverse loading of the composite to determine the effect of the ductile interphase on the yield strength. Characteristics of the ductile interphase are determined that will provide good longitudinal strength through global load sharing and a relatively high yield strength in the direction transverse to the fibers. This, in turn, will allow control of the strength anisotropy of uniaxially reinforced metal matrix composites.
23 citations
TL;DR: In this article, atomistic simulations have been used to elucidate the causes of the anomalous elastic behavior of thin films and composition-modulated superlattice materials, showing that elastic anomalies are not an electronic but a structural interface effect that is intricately connected with the local atomic disorder at the interfaces.
Abstract: Atomistic simulations are reviewed that elucidate the causes of the anomalous elastic behavior of thin films and composition-modulated superlattice materials. The investigation of free-standing thin films and of superlattices, composed of grain boundaries, shows that the elastic anomalies are not an electronic but a structural interface effect that is intricately connected with the local atomic disorder at the interfaces. The consequent predictions that (i)coherent strained-layer superlattices should show the smallest elastic anomalies and (ii) making the interfaces incoherent should enhance all anomalies, are validated by simulations of dissimilar-material superlattices. Such simulations can be an effective aid in tailoring the elastic behavior of composite materials because, in contrast with experiments, they allow one to systematically investigate simple, but well-characterized model systems with increasing complexity. This unique capability of simulations has enabled us to elucidate the underlying driving forces and, in particular, (i) to deconvolute the distinct effects due to the inhomogeneous atomic disorder, localized at the interfaces from the consequent interface-stress-induced anisotropic lattice-parameter changes and (ii) to separate the homogeneous effects of thermal disordering from the inhomogeneous effects due to the interfaces.
20 citations
TL;DR: In this article, a detailed description of equivalent crystal theory focusing on its application to the study of surface structure is presented, while the emphasis is in the structure of the algorithm and its computational aspects.
Abstract: We present a detailed description of equivalent crystal theory focusing on its application to the study of surface structure. While the emphasis is in the structure of the algorithm and its computational aspects, we also present a comprehensive discussion on the calculation of surface energies of metallic systems with equivalent crystal theory and other approaches. Our results are compared to experiment and other semiempirical as well as first-principles calculations for a variety of fcc and bcc metals.
15 citations
TL;DR: In this paper, the authors assess the merits and limitations of Hartree-Fock, density functional, semi-empirical and force field approaches in terms of capability, generality, accuracy, accessible system size, accessible time scales and computational efficiency.
Abstract: Present theoretical and computational approaches, combined with the impressive advances in computer hardware and software, open the possibility for materials design from first principles. This article presents a perspective on the relevant developments in computational chemistry, solid state physics and statistical mechanics and it assesses the merits and limitations of Hartree-Fock, density functional, semiempirical and force field approaches in terms of six criteria: capability, generality, accuracy, accessible system size, accessible time scales and computational efficiency. Functional materials for microelectronic, optical and magnetic applications currently present better opportunities for first-principles approaches than structural materials, where atomistic approaches, despite some encouraging results, are still far from capturing the full complexity of the dynamics involved in mechanical, thermal, diffusive and corrosive behavior.
13 citations
TL;DR: In this paper, the surface structure of fcc-ordered binary alloys has been studied using the semi-empirical method for alloys developed by Bozzolo, Ferrante and Smith.
Abstract: Using the semiempirical method for alloys developed by Bozzolo, Ferrante and Smith (BFS) [Bozzolo, G. et al., Phys. Rev., B45 (1992) 493] we study the surface structure of fcc-ordered binary alloys. We concentrate on the calculation of surface energies and surface relaxations for the L10- and L12 ordered structures. Different terminations of the low-index faces are studied. Also, we present results for the interlayer relaxations for planes close to the surface, revealing different relaxations for atoms of different species producing a rippled surface layer.
12 citations
TL;DR: In this article, the free energy of surfaces along the pole in gold and copper is determined to assess the effect of surface relaxation and atomic vibration on the equilibrium crystal shape of gold.
Abstract: The free energy of surfaces along the pole in gold and copper is determined to assess the effect of surface relaxation and atomic vibration on the equilibrium crystal shape of gold and copper. The Wulff construction is performed on the γ-plots to determine the equilibrium shape of gold and copper crystallites at different temperatures. It is shown that surface relaxation and atomic vibration do not have any discernible effect on the equilibrium shape of EAM gold or copper crystallites. The equilibrium shape of EAM gold crystallites is formed entirely from {111} and {100} facets, while that of EAM copper shows small {110} facets in addition to the {111} and {100} facets.
4 citations
TL;DR: In this article, two different methods have been used to simulate the structures of three-dimensional polymeric systems and tested on silica sodalite SiO, and nine metal oxides.
Abstract: Two different methods have been used to simulate the structures of three-dimensional polymeric systems and tested on silica sodalite SiO, and nine metal oxides (VO, VO2 (rutile and distorted rutile), V2O3 (corundum), TiO, TiO2 (rutile), TiO, (anatase), β-PbO2 and NiNb2O6). The first method uses traditional molecular mechanics. The structure is considered to be covalent and a large fragment is built consisting of ca. 500 atoms. Force-field parameters are then derived to reproduce the structure as accurately as possible. The edge atoms are fixed during the simulation. The second method employs the ionic structure model, where no bonds are included. Periodic boundary conditions are used and the Ewald summation is employed to calculate Coulombic energy. Van der Waals parameters are optimised to reproduce the crystal structure. Results show that the ionic structure model is more successful for oxides with distorted or irregular bonding. However, simple regular structures are modelled equally well by both methods.
4 citations
TL;DR: It is shown that the barrier to migration of the nickel ions may be overcome by interaction of the migrating ion with molecules such as H2O, NH3 and C2H2 in the supercage, thereby explaining the role of the latter species in the activation process.
Abstract: Lattice simulations and quantum mechanical techniques are used to study the energetics involved in the activation of the Ni-zeolite-Y catalyst, which requires migration of the Ni2+ cation from the S1 (hexagonal prism) to the supercage. We show that the barrier to migration of the nickel ions may be overcome by interaction of the migrating ion with molecules such as H2O, NH3 and C2H2 in the supercage, thereby explaining the role of the latter species in the activation process.
3 citations
TL;DR: In this article, the authors give a brief overview of density functional theory and discuss two specific implementations: a numerical localized basis approach (DMol) and the pseudopotential plane-wave method.
Abstract: This article gives a brief overview of density functional theory and discusses two specific implementations: a numerical localized basis approach (DMol) and the pseudopotential plane-wave method. Characteristic examples include Cu, clusters, CO and NO dissociation on copper surfaces, Li-, K-, and O-endohedral fullerenes, tris-quaternary ammonium cations as zeolite template, and oxygen defects in bulk SiO2. The calculations reveal the energetically favorable structures (estimated to be within ± 0.02 A of experiment), the energetics of geometric changes, and the electronic structures underlying the bonding mechanisms. A characteristic DMo1 calculation on a 128-node nCUBE 2 parallel computer shows a speedup of about 107 over a single processor. A plane-wave calculation on a unit cell with 64 silicon atoms using 1024 nCUBE 2 processors runs about five times faster than on a single-processor CRAY YMP.
TL;DR: In this article, the authors present a computerized procedure for the acquisition of the visual perception of a zeolite three-dimensional structure, and the interpretation of the structure in terms of elementary structural units.
Abstract: Molecular modelling techniques have demonstrated their power as helpful tools in the design of molecular sieves. Seeking to automate and optimise this step of the design process in the field of zeolite structure-property relationship studies, we present a computerised procedure for the acquisition of the visual perception of a zeolite three-dimensional structure, and the interpretation of the structure in terms of elementary structural units. The memorisation of the visual perception in a semantic network form, the prospects for its chemical interpretation and its usefulness in an artificial intelligence-oriented structure-property study, as if a ‘seeing’ computer, instead of the chemist, observes another computer screen, are presented.