Narrow Results

The effect of the periodic boundary condition (PBC) on the structure and energetics of nanotubes has been investigated by performing molecular-dynamics computer simulation. Calculations have been realized by using an empirical many-body potential energy function for carbon. A single-wall carbon nanotube has been considered in the simulations. It has been found that the periodic boundary condition has no effect at low temperature (1 K), however, it plays an important role even at intermediate temperature (300 K).

Structural stability and energetics of nickel clusters, Ni_N (N =3-459), have been investigated by molecular-dynamics simulations. A size-dependent empirical model potential energy function has been used in the simulations. Stable structures of the microclusters with sizes N = 3-55 and clusters generated from fcc crystal structure with sizes N = 79-459 have been determined by molecular-dynamics simulations. It has been found that the five-fold symmetry appears on the surface of the spherical clusters. The average coordination number shows a size-dependent characteristic, on the other hand the average nearest-neighbor distance does not show a size-dependence.

The effect of radiation damage on copper clusters has been investigated by performing molecular-dynamics simulation using empirical potential energy function for interaction between copper atoms. The external radiation is modeled by giving extra kinetic energy in the range of 5–50 eV to initially chosen atom in the cluster. It has been found that the atom having extra kinetic energy dissociates independently from the amount of given energy in the studied range.

The structural properties of single and multi-wall carbon nanotubes and the formation of carbon nanorods from multi-wall carbon nanotubes have been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that carbon nanorod formation takes place with smallest possible multi-wall nanotubes under heat treatment. On the other hand, it has been also found that single-wall carbon nanotubes are stronger than the multi-wall nanotubes against heat treatment.

Melting and fragmentation behaviors of Ni₄₂₉ cluster have been studied with molecular-dynamics simulations using a size-dependent empirical model potential energy function. To monitor thermal behaviors of the cluster, we calculated some physical quantities such as average potential energy per atom, specific heat, radial atomic distribution, bond length distribution, average interatomic distance, nearest neighbor distance and average coordination number as a function of temperature. The roles of the surface and core atoms in the melting and fragmentation process of the cluster are also investigated by considering the surface and the bulk coordination numbers of the cluster.

The structural stability of carbon nanocages, fullerens and toroids, have been investigated by performing molecular-dynamics computer simulations. The systems considered are C₁₂₀ and C₂₄₀ in ball and toroidal structures. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that C₁₂₀ ball is very unstable, and the other structures are relatively more strong against heat treatment.

The effect of chirality on the structural stability of single-wall carbon nanotubes have been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that carbon nanotube in chiral structure is more stable under heat treatment relative to zigzag and armchair models. The diameter of the tubes is slightly enlarged under heat treatment.

The structural stability of carbon nanoballs (fullerenes) C₂₀, C₆₀, and onion type C₂₀@C₆₀ has been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that C₂₀ is relatively resistive to heat treatment, however, the onion type structure is relatively less strong against heat treatment. The electronic structure of the systems considered has been also studied by performing density functional theory type calculations.

The formation of carbon nanorods from various types of carbon nanotubes has been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that carbon nanorod formed from carbon nanotubes with different chirality is not stable even at low temperature.

We have simulated the gold deposition on arsenic and gallium terminated GaAs(001) surfaces at low and room temperatures. It has been found that gallium terminated surface is relatively less stable in comparison to the arsenic terminated surface. On the other hand, a single gold adatom on the surface has different characteristics than full coverage gold atoms on the surface; a single gold atom diffuses into the surface at room temperature. Simulations have been performed by considering classical molecular-dynamics technique using an empirical many-body potential energy function comprising two- and three-body atomic interactions.

The structural properties of carbon nanorods obtained from diamond crystal have been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. Diamond nanorods have been generated from three low-index planes of diamond crystal. It has been found that the average coordination number, cross-section geometry, and surface orientation from which the nanorod is generated play a role in the stability of diamond nanorods under heat treatment. The most stable diamond nanorod has been obtained from the (111) surface.

An empirical many-body potential energy function has been developed to investigate the structural features and energetics of Zn_kCd_l (k+l=3, 4) microclusters. The most stable structures were found to be triangular for the three-atom clusters and tetrahedral for the four-atom clusters. The present results are in good agreement with available literature values.

Junction formation in crossed C(10,0) single wall carbon nanotubes under pressure has been investigated, using classical molecular-dynamics simulations at 1 K. It has been found that a stable mechanical junction was formed by means of placing two crossed single wall carbon nanotubes between two rigid graphene layers which move toward each other.

In a recent work, a dense fluid flow across a nanoscopic thin plate was simulated by means of Molecular Dynamics (MD) and Lattice Boltzmann (LB) methods. It was found that in order to recover quantitative agreement with MD results, the LB simulation must be pushed down to sub–nanoscopic scales, i.e. fractions of the range of molecular interactions. In this work, we point out that in this sub–nanoscopic regime, the LB method works outside the hydrodynamic limit at the level of a single cell spacing. A quantitative comparison with the Navier–Stokes (NS) solution shows however that LB and NS results are quite similar, thereby indicating that, apart for a small region past the plate, this nanoflow is still well described by hydrodynamic equations.

In this paper, the melting behaviors of the glasslike cluster Au₁₉ are calculated and analyzed by using standard microcanonical molecular-dynamics simulations. The calculated results show a multi-step melting process. The first stage involves the majority of the surface atoms (14 atoms). An interesting phenomenon is that the minority of the surface atoms (4 atoms) are still in a solid-like state. The second stage involves all of the surface atoms. But there are two sites where the atoms stay for a relatively long time. The third stage corresponds to the frequent isomerizations involving all the surface atoms. The final stage consists of isomerization transitions involving all of the atoms, including the central atom of the cluster. The unique melting processes lead to the unique features of the caloric curve, the root-mean-square bond-length fluctuation and the heat capacity of the glasslike Au₁₉.

In this paper, the geometric structures and the melting-like processes of the 13-atom pure copper, pure cobalt cluster and their 13-atom mixed clusters are investigated and compared by the molecular dynamics method. The calculation shows that the pure copper and cobalt clusters have the standard icosahedral structures and the mixed clusters take on the deformed icosahedral structures. The quantitative analysis shows that the deformations are slight. Moreover, an element similarity function is introduced by which the contribution of the compositions of the clusters to the deformation of the mixed clusters is analyzed and discussed. With the increase of the temperature, the migrating and recombination of the atoms on the surface of the clusters are observed, indicating the starting of the transition from solid-like to liquid-like state for the clusters. Through the calculating of the relative root-mean-squared pair separation fluctuation and monitoring the dynamical structures of the clusters, it is found that the mixed clusters experience a multi-step process in the transition.

By using the standard microcanonical molecular-dynamics simulations, the melting behaviors of the clusters bound by Gupta potentials are investigated. The calculations indicate that these clusters can show different melting behaviors. The origins of these processes are studied. The effects of the attractive range and the repulsive part of the interatomic interaction on the melting behaviors of the clusters are compared and analyzed.