Adham Hashibon

Atomistic study of structural correlations at a liquid–solid interface

Abstract Structural correlations at a liquid–solid interface were explored with molecular dynamics simulations of a model aluminium system using the Ercolessi–Adams potential and up to 4320 atoms. Substrate atoms were pinned to their equilibrium crystalline positions while liquid atoms were free to move. The density profile at the interface was investigated for different substrate crystallographic orientations and temperatures. An exponential decay of the density profile was observed, ρ ( z )∼e − κz , leading to the definition of κ as a quantitative measure of the ordering at the liquid solid interface. A direct correlation between the amount of ordering in the liquid phase and the underlying substrate orientation was found.

Ordering at Solid-Liquid Interfaces Between Dissimilar Materials

In an earlier report we explored structural correlations at a liquid-solid interface with molecular dynamics simulations of a model aluminium system using the Ercolessi-Adams potential and up to 4320 atoms. Substrate atoms were pinned to their equilibrium fcc crystalline positions while liquid atoms were free to move. A direct correlation between the amount of ordering in the liquid phase and the underlying substrate orientation was found. In the present paper we extend this study to the case of a fixed bcc substrate in contact with liquid aluminium. We find surprisingly similar results for the density profiles of both (100) and (110) substrates. However, there is a far greater in-plane ordering in the (100) than for the (110) system. For the (100) substrates we observe adsorption of liquid atoms into the terminating plane of the bcc (100) substrate, effectively transforming the bcc (100) plane into an fcc (100) plane.

Visualization of electronic density

The spatial volume occupied by an atom depends on its electronic density. Although this density can only be evaluated exactly for hydrogen-like atoms, there are many excellent algorithms and packages to calculate it numerically for other materials. Three-dimensional visualization of charge density is challenging, especially when several molecular/atomic levels are intertwined in space. In this paper, we explore several approaches to this, including the extension of an anaglyphic stereo visualization application based on the AViz package for hydrogen atoms and simple molecules to larger structures such as nanotubes. We will describe motivations and potential applications of these tools for answering interesting physical questions about nanotube properties

Visualization for Molecular Dynamics of Solids

We have developed an approach to three-dimensional visualization suitable for molecular dynamics and simulated annealing modelling projects. We discuss the reasons for our software selection and development as well as the technical basis of the approach, and describe a video illustrating some of these calculations.

Visualization and Real-Time Collaboration over Internet-2

We report on recent efforts in our research group to visualize data sets resulting from atomistic simulations, and to communicate these visualizations over high-bandwidth internet connections.

Visualization in the integrated SimPhoNy multiscale simulation framework

Abstract We describe three distinct approaches to visualization for multiscale materials modelling research. These have been developed with the framework of the SimPhoNy FP7 EU-project, and complement each other in their requirements and possibilities. All have been integrated via wrappers to one or more of the simulation approaches within the SimPhoNy project. In this manuscript we describe and contrast their features. Together they cover visualization needs from electronic to macroscopic scales and are suited to simulations made on personal computers, workstations or advanced High Performance parallel computers. Examples as well as recommendations for future calculations are presented.

Roughening Transitions in HCP Lattices

Direct observation of three equilibrium roughening transitions (at about one degree Kelvin) for HCP He4 was possible because equilibrium between the solid and superfluid phases of helium can be reached on the scale of seconds. While this provides an exciting opportunity for comparison between experimental data and models for the roughening transition, the non-Bravais nature of the HCP lattice severely complicates direct simulations. Using computer visualization to simplify the HCP sample preparation, and parallel algorithms to speed up the calculations, we have been able to evaluate roughening temperatures for three facets and directly estimate the surface tension for many temperatures. Substantial agreement with the experimental data was found.

Numerical simulations of roughening temperatures in a hexagonal van-der-Waals4He crystal

We have carried out numerical simulations to investigate roughening on4He crystal surfaces. Algorithms were constructed for an h.c.p. crystal, incorporating van-der-Waals interatomic interactions. The Wulff plot was calculated at 0 K. Also, by sectioning the crystal in several symmetry directions, roughening temperatures, TR, have been calculated for these orientations using a lattice-gas model. In particular, these have been determined for thec, a ands facets, as well as for lower-symmetry facets which involve interactions between higher-than-nearest-neighbours. On one of these facets, we have observed the formation of anisotropic clusters below a certain critical temperature. The values for the high-symmetry facets are more precise but in broad agreement with those calculated by Touzani and Wortis1 and do not agree particularly well with the observed values. We are therefore investigating quantum corrections to the calculations.