Predicting large area surface reconstructions using molecular dynamics methods.

In this paper we discuss a new simulation method that can be used to predict preferred surface reconstructions of model systems by Molecular Dynamics (MD). The method overcomes the limitations imposed by periodic boundary conditions for finite boundary MD simulations which can normally prevent reconstructions. By simulating only the reconstructed surface layer and by removing the periodic boundary effects and the free energy barriers to reconstruction, the method allows surfaces to reconstruct to a preferred structure.

Computation of thermodynamic and transport properties to predict thermophoretic effects in an argon-krypton mixture.

Thermophoresis is the movement of molecules caused by a temperature gradient. Here we report the results of a study of thermophoresis using non-equilibrium molecular dynamics simulations of a confined argon-krypton fluid subject to two different temperatures at thermostated walls. The resulting temperature profile between the walls is used along with the Soret coefficient to predict the concentration profile that develops across the channel.

Linear and nonlinear density response functions for a simple atomic fluid.

We use molecular dynamics simulations to investigate the linear and nonlinear density response functions for simple fluids under the influence of spatially periodic external fields. Using a direct Fourier space decomposition of the instantaneous microscopic density for the perturbed fluid we can clearly identify the distinct order of response. Using a single component sinusoidal longitudinal force for a set of wavelengths and amplitudes we show that in the linear response regime the proportionality between the external field amplitude and the density perturbation can be used to determine the linear density response function, and hence the pair correlation function, static liquid structure factor, and lowest order direct correlation function.

Site-dependent stability and electronic structure of single vacancy point defects in hexagonal graphene nano-flakes.

Graphene nano-flakes and quantum dots have considerable potential as components for nanodevices, since the finite in-plane dimension and additional edge and corner states provide potential for band gap engineering. However, like semi-infinite graphene membranes, they may contain different configurations of vacancy point defects that may be difficult to predict or control. In this paper we use density functional tight binding simulations to explore the impact of different geometric configurations of vacancies in unterminated (radical), mono-hydride and di-hydride terminated nano-flakes with zigzag or armchair edges.

Motion, relaxation dynamics, and diffusion processes in two-dimensional colloidal crystals confined between walls.

The dynamical behavior of single-component two-dimensional colloidal crystals confined in a slit geometry is studied by Langevin dynamics simulation of a simple model. The colloids are modeled as pointlike particles, interacting with the repulsive part of the Lennard-Jones potential, and the fluid molecules in the colloidal suspension are not explicitly considered. Considering a crystalline strip of triangular lattice structure with n=30 rows, the (one-dimensional) walls confining the strip are chosen as two rigidly fixed crystalline rows at each side, commensurate with the lattice structure and, thus, stabilizing long-range order.