Continuum modeling using the Lennard-Jones potential has been shown to provide a good estimation for the interaction energy between regular-shaped homogeneous molecules comprising the same type of atoms. However, this method may not be accurate for heterogeneous molecules, which are made up of more than one chemical element. The traditional method to deal with this involves approximating the molecule via multiple surfaces in a piecemeal fashion. While this approach works well for small sized molecules, calculations become intensive for large sized molecules as a large number of sums from multiple surface interactions are involved. To address this issue, we propose a new model that approximates a heterogeneous molecule with a single surface or volume, where attractive and repulsive constants (A and B) in the Lennard-Jones potential are replaced by functions A(r) and B(r), which depend on the parameterization of the surface r. We comment that this technique is suitable for regular-shaped nanostructures where their heterogeneity can be modeled by surface (or volume) parameterization. Validation of the new approach is carried out via two problems, namely, carbon nanotube–methane and carbon nanotube–coronene interactions. For coronene and methane, which are assumed to be radially symmetric, we propose A(r) and B(r) to be sigmoidal functions for which the interaction strength decreases from the inner region of the carbon atoms toward the outer region of the hydrogen atoms. Our results for both cases show that using the sigmoidal profiles for A(r) and B(r) gives rise to interaction energies that are in better agreement with those obtained from molecular dynamics studies compared to results using constant A and B. The new approach provides a significant improvement to the current continuum modeling using the Lennard-Jones potential.

The Lennard–Jones potential and a continuum approach can be used to successfully model interactions between various regular shaped molecules and nanostructures. For single atomic species molecules, the interaction can be approximated by assuming a uniform distribution of atoms over surfaces or volumes, which gives rise to a constant atomic density either over or throughout the molecule. However, for heterogeneous molecules, which comprise more than one type of atoms, the situation is more complicated. Thus far, two extended modeling approaches have been considered for heterogeneous molecules, namely a multi-surface semi-continuous model and a fully continuous model with average smearing of atomic contribution. In this paper, we propose yet another modeling approach using a single continuous surface, but replacing the atomic density and attractive and repulsive constants in the Lennard–Jones potential with functions, which depend on the heterogeneity across the molecules, and the new model is applied to study the adsorption of coronene onto a graphene sheet. Comparison of results is made between the new model and two other existing approaches as well as molecular dynamics simulations performed using the LAMMPS molecular dynamics simulator. We find that the new approach is superior to the other continuum models and provides excellent agreement with molecular dynamics simulations.

Methane capture and storage are of particular importance for the development of new technology to reduce the effects of climate change and global warming. Carbon-based nanomaterials are among several porous nanomaterials proposed as potential candidates for methane storage. In this paper, we adopt a new continuum approach with functional Lennard-Jones parameters to provide interaction energies for methane inside carbon nanostructures, namely fullerenes, nanotube bundles, and nanocones. This study provides a significant improvement to previous continuum modeling approaches using the Lennard-Jones potential.

Articles you may be interested inStoichiometry changes by selective vacancy formation on (110) surfaces of III-V semiconductors: Influence of electronic effects New surface atomic structures for column V overlayers on the (110) surfaces of III-V compound semiconductorsInterfaces formed between metals (In, Ag) and cleaved (110) surfaces of III-V compound semiconductors (GaSb, GaAs) held at low temperature are studied with low-energy electron diffraction and electron energy-loss spectroscopy. We consider the unrelaxation of the semiconductor surface structure by the metal adatoms, the adsorption sites on the surface and their implications for semiconductor band bending. The results are discussed in light of recent scanning tunneling microscopy measurements on metal/semiconductor interfaces and tight binding calculations of preferential adsorption sites.

The production of single dimensional carbon structures has recently been made easier using carbon nanotubes. We consider here encapsulated coronene molecules, which are flat and circular-shaped polycyclic aromatic hydrocarbons, inside carbon nanotubes. Depending on the radius of the nanotube, certain specific configurations of the coronene molecules can be achieved that give rise to the formation of stacked columns or aid in forming nanoribbons. Due to their symmetrical structure, a coronene molecule may be modelled by three inner circular rings of carbon atoms and one outer circular ring of hydrogen atoms, while the carbon nanotube is modelled as a circular tube. Using the continuous model and the Lennard-Jones potential, we are able to analytically formulate an expression for the potential energy for a coronene dimer and coronene inside a carbon nanotube. Subsequently, stacking of coronene molecules inside a nanotube is investigated. We find that the minimum energy tilt angle of coronenes in a stack differs from that of a single coronene within the same nanotube. More specifically, for both (18, 0) and (19, 0) zigzag carbon nanotube, we find that the minimum energy tilt angles of the single coronene case (≈42 ° and ≈20 ° respectively) do not occur in the stack model.

Sliding friction levels of thin (1-2 monolayers) and thick (~10 monolayers) oxygen films adsorbed on nickel and gold at 47.5 K have been measured by means of a quartz crystal microbalance (QCM) technique. Friction levels for the thin (thick) films on nickel in the presence of a weak magnetic field were observed to be approximately 30% (50%) lower than those recorded in the absence of the external field. Friction levels for thin films on gold were meanwhile observed to be substantially increased in the presence of the field. Magnetically-induced structural reorientation (magnetostriction) and/or realignment of adlayer spins, which respectively reduce structural and magnetic interfacial corrugation and commensurability, appear likely mechanisms underlying the observed field-induced reductions in friction for the nickel samples. Eddy current formation in the gold substrates may account for the increased friction levels in this system. The work demonstrates the role of magnetic effects in model systems that are highly amenable to theoretical studies and modeling.Condens. Matter 2019, 4, 1 2 of 13 impact friction. These include magnetostrictive shape changes in solids [21][22][23], as well as viscosity and magnetorheological stiffness changes in liquids [24], which alter interfacial commensurability and, thus, the phononic contributions to friction [2][3][4].Experimental studies targeting magnetic dissipative mechanisms to date have been very limited in number, and have employed asperity-substrate geometries in either contact [12] or non-contact geometries [19]. Although planar interfacial geometries remain virtually unexplored, a variety of fascinating dissipative phenomena have been theoretically predicted, in association with varying degrees of magnetic commensurability and/or interfacial spin corrugation [11]. Kadau et al., for example, studied the intrinsic magnetic interaction between two magnetic planes of magnetic materials, both of which were insulating so as to avoid conduction electron and eddy current effects. One major finding of the study was that that anti-ferromagnetic interfaces resulted in significantly higher friction levels than ferromagnetic interfaces. Planar geometries are also amenable to modeling of the magnetic and electronic properties of a wide range of magnetic materials. For the present study, we employed oxygen films, which are paramagnetic, adsorbed in a planar geometry on ferromagnetic nickel substrates and nonmagnetic gold substrates in the presence and absence of weak external magnetic fields, to explore whether the fields could be used to actively tune adsorbate friction levels.Numerous experimental and theoretical studies have confirmed magnetically ordered monolayers for the solid phases of adsorbed oxygen, including an antiferromagnetic phase [25,26]. When exposed to an external field, such layers, when adsorbed on graphite, are reported to exhibit behavior more characteristic of a ferromagnet than a paramagnet, achieving saturated magnetism even in the presence of weak external ...

Carbon nanostructures are of particular interest as platforms for molecular storage and adsorption. In this paper, the adsorption of a single stranded DNA molecule onto a graphene sheet is considered. Even though DNA molecules are complicated heterogeneous structures comprising several types of atoms, it is found that the repeated patterns within the DNA molecules enable the use of a continuum approach to model the DNA‐graphene sheet interaction. Here, a model is proposed such that the heterogeneity across the DNA molecule is captured by interaction functions, which are used to replace the attractive and repulsive constants in the Lennard‐Jones potential. Result from this new model shows better agreement to molecular dynamics simulations compared to the traditional continuum approach where atoms on the DNA are averaged evenly across the molecule. Finally, the paper comments on the model, its parameters, and suggests ways for improvement.

The catalytic effect of graphene on the corannulene bowl-to-bowl inversion is confirmed in this paper using a pair-wise dispersion interaction model. In particular, a continuum approach together with the Lennard-Jones...