No abstract available

No abstract available

No abstract available

[en] An expression is presented for computing the classical diffusion constant of a point defect (e.g., an adatom) in an infinite lattice of binding sites at arbitrary temperature. The transition state theory diffusion constant is simply multiplied by a dynamical correction factor that is computed from short-time classical trajectories initiated at the site boundaries. The time scale limitations of direct molecular dynamics are thus avoided in the low- and middle-temperature regimes. The expression results from taking the time derivative of the particle mean-square displacement in the lattice-discretized coordinate system. Applications are presented for surface diffusion on fcc(100) and fcc(111) Lennard-Jones crystal faces

[en] A characterization of crystallographic unit cells as vectors in a Euclidean six-dimensional space (E⁶ in the usual mathematical notation; here termed G⁶) is introduced, in which the non-triclinic Bravais lattice types form one-, two-, three- and four-dimensional linear subspaces. This formalism makes the determination of the 'best' Bravais lattice (or lattices) for a particular experimentally determined cell a process of determining Euclidean distances in G⁶ from the cell to its projections into the subspaces of the lattice types. The elements of vectors in the space are drawn from the Niggli matrix with the unsymmetrical elements doubled. A cell is first reduced and all its nearly Buerger-reduced cells are used in the distance determinations. Thus the smallest distance provides information about both the propriety of the lattice type selection and the instability of the cell reduction. (orig.)

[en] In many problems in molecular and solid state structures one seeks to determine the energy-minimizing decoration of sites with different atom types. In other problems, one is interested in finding a decoration with a target physical property (e.g. alloy band gap) within a certain range. In both cases, the sheer size of the configurational space can be horrendous. We present two approaches which identify either the minimum-energy configuration or configurations with a target property for a fixed underlying Bravais lattice. We compare their efficiency at locating the deepest minimum energy configuration of face centered cubic Au-Pd alloy. We show that a global-search genetic-algorithm approach with diversity-enhancing constraints and reciprocal-space mating can efficiently find the global optimum, whereas the local-search virtual-atom approach presented here is more efficient at finding structures with a target property

No abstract available

[en] First principles calculations show that two-body forces are sufficient to describe interactions of He with fcc Cu and bcc Nb. This property is explained directly from calculated charge density distributions and used to construct a Cu–Nb–He interatomic potential that predicts accurate He impurity energies despite not being fitted to them

[en] The phononic band structures of three-dimensional solid phononic crystals consisting of three types of lattices (face centred cubic, body centred cubic and simple cubic) with four different shapes (spherical, cubic, rhombic dodecahedral and truncated octahedral) of scatterers are studied numerically. The results show that reorienting of non-spherical scatterers can change the size of the band gap. For all kinds of shaped scatterers, the face centred cubic lattice is the optimal array structure. For each lattice the shape of scatterers that can generate the largest gaps is also presented

[en] A variety of ideal close-packing structures were constructed using a stacking mechanism with rhombus, square and triangular nets of atoms interrelated by a common angular parameter. The structural features of the resulting space lattice are greatly influenced by the sequence and mode of stacking and the type of net. It was found that stacking by AB sequence yields structures of highest symmetry whereas stacking via a central mode results in structures of higher coordination number and packing density. The importance of symmetry in determining the most probable structures is highlighted and a generalized description of ideal close-packing structures is proposed. (orig.)