Search results for "molecular dynamics"
showing 10 items of 1075 documents
Quenched molecular dynamics studies on the extraction energy of aluminum atoms
2007
The extraction energy of an aluminum atom is calculated at 0 K as a function of coordination number and defect depth for three surface orientations [(100), (110) and (111)]. For each orientation, atoms are selected and extracted one by one. A linear relationship is obtained between the extraction energy of surface atoms and their coordination numbers (with slight variations due to the geometrical configuration of the atoms). However, the study of the influence of the defect depth on the extraction energy highlights the role played by intrinsic stress on the extraction energy. Copyright © 2008 John Wiley & Sons, Ltd.
Structure and Dynamics of the Instantaneous Water/Vapor Interface Revisited by Path-Integral and Ab Initio Molecular Dynamics Simulations
2015
The structure and dynamics of the water/vapor interface is revisited by means of path-integral and second-generation Car-Parrinello ab-initio molecular dynamics simulations in conjunction with an instantaneous surface definition [A. P. Willard and D. Chandler, J. Phys. Chem. B 114, 1954 (2010)]. In agreement with previous studies, we find that one of the OH bonds of the water molecules in the topmost layer is pointing out of the water into the vapor phase, while the orientation of the underlying layer is reversed. Therebetween, an additional water layer is detected, where the molecules are aligned parallel to the instantaneous water surface.
Noble-gas bubbles in metals: Molecular-dynamics simulations and positron states.
1987
A theoretical treatment of atomic structure and positron states in noble-gas bubbles in metals is presented. The Al-He and Cu-Kr systems are considered as specific examples. For large bubbles (radii above a few tens of angstroms) a calculational scheme is developed combining molecular-dynamics results for the metal--noble-gas interface with positron calculations. It is demonstrated that a positron is trapped at the surface of a noble-gas bubble, i.e., at the metal-gas interface. The annihilation rate with metal electrons is similar to that at a clean surface, while simultaneously there is a significant annihilation rate with gas-atom electrons. This enables relationships between the gas den…
Roughening of the Cu(110) surface
1993
The structure of the Cu(110) surface is studied at high temperatures using a combination of lattice-gas Monte Carlo and molecular dynamics methods with identical many-atom interactions derived from the effective medium theory. The anisotropic six-vertex model is used in the interpretation of the lattice-gas results. We find a clear roughening transition around T_R=1000K and T_R/T_M=0.81. Molecular dynamics reveals the clustering of surface defects as the atomistic mechanism of the transition and allows us to estimate characteristic time scales. For the system of size 50x50, the time scale of the local roughening at 1150 K of an initially smooth surface is of the order of 100 ps.
Grain size, stress and surface roughness
2008
In this article, we report molecular dynamics (MD) simulations on the formation of roughness at the surface of strained polycrystalline aluminum samples at 300 K. The computed roughness increases as a function of applied strain but does not follow a linear law for all applied strains. A linear relationship with a small slope is obtained in the elastic domain. Then, the roughness increases rapidly with the applied strain in the plastic domain studied. Moreover, the surface roughness increases as a function of grain size (between 5 and 20 nm) in the plastic domain (<6%).
Numerical and theoretical considerations on the surface energy for pure solids under strain
2004
In this paper we developed a numerical analysis, by means of molecular dynamics (MD) simulations, for the surface energy of solids when a stress is applied parallel to the surface. Our MD simulations for Al showed that under these conditions; compression or an alternation of compression and tension, with respect to the bulk, of some atomic layers below the surface is present. Moreover, we quantified the surface energy variations that led us to propose an empirical model.
Kirkwood–Buff Integrals Using Molecular Simulation: Estimation of Surface Effects
2020
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Polymer Brushes on Flat and Curved Substrates: Scaling Concepts and Computer Simulations
2007
The scaling concepts for isolated flexible macromolecules in good solvent grafted with one chain end to a flat surface (polymer mushrooms) as well as for layers of many overlapping end-grafted chain molecules (polymer brushes) are introduced. Monte Carlo attempts to test these concepts are briefly reviewed. Then the extension of these concepts to polymer brushes grafted to the interior of a cylinder surface is discussed. Molecular Dynamics results on chain average linear dimensions in the direction normal to the grafting surface and in axial direction are described, as well as distribution functions for the density of end monomers and of all monomers of the chains. It is argued that under t…
Molecular Dynamics Study of Disordering and Premelting of the Pb(110) Surface
1994
Molecular dynamics simulations incorporating a many-body (glue) potential have been used to investigate the atomic structure and dynamics of the Pb(110) surface in the range from room temperature up to the bulk melting point. The Pb (110) surface starts to disorder approximately at 360 K via the generation of vacancies and the formation of an adlayer. At about 520 K we observe the onset of a quasiliquid region at the surface, which exhibits liquid-like energetic, structural and surface properties. The disordering is enhanced in the direction parallel to the close-packed rows. While losing long range order, the two outermost quasiliquid layers retain a considerable degree of short range orde…
Static and dynamical properties of a supercooled liquid confined in a pore
2000
We present the results of a Molecular Dynamics computer simulation of a binary Lennard-Jones liquid confined in a narrow pore. The surface of the pore has an amorphous structure similar to that of the confined liquid. We find that the static properties of the liquid are not affected by the confinement, while the dynamics changes dramatically. By investigating the time and temperature dependence of the intermediate scattering function we show that the dynamics of the particles close to the center of the tube is similar to the one in the bulk, whereas the characteristic relaxation time tau_q(T,rho) of the intermediate scattering function at wavevector q and distance rho from the axis of the p…