Effect of Potential Function on Molecular Dynamics Simulation of Copper Processing

Nowadays, the nano-machining process is used to produce high quality finished surfaces with precise form accuracy. To understand and analyze the chip formation mechanism of nano-machining process on an atomistic scale, since the experimentation is not an easy task, numerical simulation such as molecular dynamic (MD) simulation is a very useful method. In this paper, MD simulation of the nano-metric cutting of single-crystal copper was performed with a single crystal diamond tool. The model was solved with both pair wise Morse potential function and embedded atom method (EAM) potential to simulate the inter-atomic force between the work-piece and a rigid tool. The chip formation mechanism, dislocation generation, tool forces and generated temperature were investigated. Results show that the Morse potential cannot perform an appropriate defect formation and plastic deformation in nano-metric cutting of metals. Also, tool forces in Morse potential are more than the forces in EAM potential. Furthermore, the fluctuations of resultant forces in Morse potential are greater than that of EAM. In addition, using many-body interaction potentials like EAM can lead to substantial changes in surface energies, elastic-plastic properties and atomic displacement, compared with the pair-wise potentials like Morse. Finally, the atomic displacement investigation shows that in EAM potential study, only the atoms in a local region near the cutting process are displaced, but in Morse potential a large portion of atoms has affected during cutting process. Subsequently, the chip temperature in EAM potential is more than that of Morse potential.

We have carried out a complete calculation of the various thermodynamic properties of Kr and Xe from the (${\ensuremath{\lambda}}^{4}$) anharmonic perturbation theory proposed by Shukla and Cowley [Phys. Rev. B 3, 4055 (1971)], where \ensuremath{\lambda} is the Van Hove ordering parameter. To illustrate the effect of different potential functions on the various calculated thermodynamic properties, we have employed a nearest-neighbor central force model with the Lennard-Jones (LJ), Morse, and Rydberg interaction potentials. Along with the ${\ensuremath{\lambda}}^{4}$ results, we also present the results for the quasiharmonic (QH) and the ${\ensuremath{\lambda}}^{2}$ perturbation theory for all three potentials for each of Kr and Xe rare-gas solids. The LJ QH results are qualitative for most of the thermodynamic properties of Kr and Xe and best QH results are obtained with the Rydberg potential. The ${\ensuremath{\lambda}}^{2}$ perturbation theory results are poor beyond (1/3)${T}_{m}$ (${T}_{m}$ is the melting temperature) for the LJ potential and somewhat better for the Morse and Rydberg potentials. Best results for \ensuremath{\beta} (volume expansivity) and ${C}_{p}$ (specific heat at constant pressure) are obtained with the ${\ensuremath{\lambda}}^{4}$ theory and the Morse potential. The convergence of the perturbation expansion improves with the addition of ${\ensuremath{\lambda}}^{4}$ contributions and the expansion remains valid up to 40% of ${T}_{m}$ for the LJ potential. The range of expansion is much higher for the other two potentials. Whereas the curvature of most of the calculated curves for the various thermodynamic properties for the ${\ensuremath{\lambda}}^{2}$ theory is incorrect, the corresponding curves from the ${\ensuremath{\lambda}}^{4}$ theory have the correct curvature. The cancellation among the ${\ensuremath{\lambda}}^{2}$ and ${\ensuremath{\lambda}}^{4}$ contributions is most dramatic for the LJ potential and less so for the other two potentials. As T approaches ${T}_{m}$, only the Rydberg-potential results, for the ${\ensuremath{\lambda}}^{2}$ theory, appear to be sensible compared with the other two potentials for most of thermodynamic properties of Kr and Xe.

A molecular dynamics simulation considered of chip deformation and force analysis for grinding process of Mg-Al alloy is presented. Hybrid potentials including embedded atom method (EAM) potential and Morse potential are applied in this model. The activities among atoms of Mg-Al Alloy material is described by EAM potential which is very suitable for metal materials. Morse potential is used to realize the interaction between Mg-Al alloy and abrasive grain made of diamond. Simulations of Different depths of cut (0.6nm, 0.8nm and 1.0nm) and different cut speeds (50m/s, 100m/s and 200m/s) are given. The experience result shows that with the same nanometric depth of cut, there is a little difference of ratio of the cut potential to the cutting speed. Moreover, with the same cutting speed, the cut potential is increased linearly with the depth of cut while reaching to stable cutting regime.

This paper develops a relationship between the Morse potential and the Murrell-Mottram's 2-body potential. By expressing both potentials in terms of a repulsive term and an attractive term, and approximating Maclaurin's expansion, comparison of coefficients and indices of the repulsive and attractive terms leads to parametric connections between these two potential functions. Non-dimensional curves of these potentials at long range show good agreement as compared to those obtained previously. A set of parametric relationships obtained recently, together with the presently proposed connections, are useful in paving a way for the development of a potential function converter.

Controlled variation in catalyst-electrode potential of metals interfaced with solid electrolytes leads to the effect of Non-faradaic Modification of Catalytic Activity (NEMCA) which causes dramatic changes in the catalytic activity and selectivity. Its origin was shown to lie in the controlled variation of the work function upon polarization of the catalyst-solid electrolyte interface which is due to ion spillover over the entire gas exposed catalyst surface. In the present work the effect of induced work function changes on the kinetics and energetics of the interaction of oxygen with polycrystalline Pt, interfaced with an yttria stabilized zirconia solid electrolyte, were studied, by means of the temperature programmed desorption technique. It was found that by increasing catalyst potential and work function the O2 desorption peak shifts towards lower temperatures, showing that the binding strength of chemisorbed oxygen species weakens by increasing catalyst work function. The activation energy of desorption of adsorbed O species was measured by the “temperature rate variation technique” and was found to decrease linearly with slope -1 with increasing catalyst work function. This straightforward experimental correlation between catalyst work function and the binding energy of chemisorbed O species is in absolute agreement with previous NEMCA studies which show that the apparent activation energy of all reactions studied, depends linearly on catalyst potential and work function.

The deposition process of copper onto silicon substrate was studied by the molecular dynamics method. Tersoff, MEAM, and Morse potentials were used to describe the interaction of Si-Si Cu-Cu, and Cu-Si, respectively. Deposition process was performed using NVE ensemble and applying Berendsen thermostat with 0,2 fs timestep for 100 ps. The effect of substrate temperature on the percentage of amorphous structure, radial distribution function (RDF), and coordination number was investigated. The result was indicated that at 300 K, the percentage of amorphous structure was relatively lower compared to another temperature. First peaks of RDF at each temperature were found at radius 3,05 Å and were still relatively wide, indicating short-range order structure.

Soft materials, such as gold, play a crucial role in solid-state devices for the electronics industry, biochemical sensors, and miniaturized medical machinery. This study investigates the abrasive behavior and friction properties of the rough surface of polycrystalline Au material through a shearing process using molecular dynamics (MD). The effects of friction velocity and temperature are explored by analyzing the force-time curve, crystal evolution, shear strain distribution, differential distribution, and atomic flow direction. Temperature affects polycrystalline Au more deeply; almost crescent-peak regions of Au transform into an amorphous structure upon contact with abrasive Ni at shearing temperatures of 450 and 600K, while atoms vibrate around their equilibrium positions. The compress simulation shows the different behavior of the Au material under various potentials. At lower abrasive velocities, atomic movement and the deformation region are more pronounced. The normal force increases with an increase in abrasive velocity from 20 to 100m/s or a temperature rise from 150 to 450K; however, it decreases as the abrasive velocity reaches 150m/s or when the temperature increases to 600K. The ATOMSK program is applied to create the polycrystalline Au and Ni structures. The MD method is employed to investigate the influence of various friction velocities and temperatures on the force-time curve, crystal evolution, shear strain distribution, differential distribution, and atomic flow direction of polycrystalline Au alloys. The simulation process is performed via LAMMPS software. The visualization tool (OVITO) is borrowed to examine, evaluate, and demonstrate the simulation results. The Morse potential is used to describe the interaction forces between Ni-Ni, Au-Au, and Ni-Au.

Bi-materials in submicron scale have been widely used in many industries, especially in the microelectronics industry. Due to the different deformation between the two material layers, damage usually occurs on the surface between the two material layers. In this paper, the Molecular dynamics (MD) method is used to investigate the mechanical properties of bi-material Ni/Al under the tensile strain. The examined Ni/Al structure has dimensions of 10.90 nm x 5.27 nm x 4.22 nm/10.93 nm x 5.26 nm x 4.21 nm, with strain rates of 1.83x108s-1, 5.48x108s-1, 1.83x109s-1 and 5.48x109s-1, respectively. The interactions between the atoms in the system are described by the EAM (Embedded Atom Method). The calculated results show that Young's modulus of bi-material Ni/Al does not change under the various strain rates, while the fracture strength of Ni/Al increases with increasing of the strain rates. In addition, the effects of load position and temperature on the fracture strength of Ni/Al are also investigated. With the strain rate of 1.83x108 s-1, the fracture strength of Ni/Al at 100oK and 700oK is 6.6 GPa and 4.3 GPa, respectively. The obtained results of the study are helpful in the design and fabrication of devices based on the bi-material Ni/Al.

The objective of this paper is to demonstrate how Morse potentials can be modified to better approximate experimentally determined melting points of materials. Morse potentials are typically fit to, and in agreement with, zero temperature properties such as bond energy, equilibrium bond length, and force constant. However, high temperature properties are often very inaccurate. The gap this paper seeks to address is the lack of a systematic approach to development of simple interatomic potentials which can address both high temperature and low temperature material properties. In principle, these potentials should utilize physics informed analytical functional forms and have a small number of fitting parameters. Our approach for development of a modified Morse potential (MMP) is to connect three component Morse potentials (CMP) that differ by force constant via smoothing functions. The CMPs are responsible for different MMP regions which are defined by distance between atoms. The left-hand CMP is responsible for the repulsive part of the MMP, the unmodified Morse potential (UMP) is responsible for the bottom of the potential well, and the right-hand CMP is responsible for the attractive part of the MMP. The force constants of the left-hand CMP and right-hand CMP can be larger or smaller values than the UMP, which results in a stiffer or looser MMP at distances between atoms that would be sampled at high temperatures, far from the bottom of the potential well. This added flexibility allows the MMP to be tuned to the predicted melting point while preserving the zero temperature properties inherited from the original UMP. This work is motivated by the in-pile instrumentation program which has developed additively manufactured melt wires for measuring the temperature of operating nuclear reactors.

Using the density functional B3P86/cc-PV5Z method, the geometric structure of BH molecule under different external electric fields is optimized, and the bond lengths, dipole moments, vibration frequencies, and other physical properties parameters are obtained. On the basis of setting appropriate parameters, scanning single point energies are obtained by the same method and the potential energy curves under different external fields are also obtained. These results show that the physical property parameters and potential energy curves may change with external electric field, especially in the case of reverse direction electric field. The potential energy function without external electric field is fitted by Morse potential, and the fitting parameters are obtained which are in good agreement with experimental values. In order to obtain the critical dissociation electric parameter, the dipole approximation is adopted to construct a potential model fitting the corresponding potential energy curve of the external electric field. It is found that the fitted critical dissociation electric parameter is consistent with numerical calculation, so that the constructed model is reliable and accurate. These results will provide important theoretical and experimental reference for further studying the molecular spectrum, dynamics, and molecular cooling with Stark effect.

There are conflicting reports concerning the effect of female age and potential reproductive function. We assessed the response to ovarian hyperstimulation in two consecutive IVF cycles in 25 women greater than 35 years of age and compared their response to a control group of 48 women less than 35 years of age who conceived in our IVF programme. In the older women, the maximal oestradiol response was proportional to the number of vials of HMG used and did not differ from the response of the younger women. Similarly, the number of follicles of diameter greater than 1.0 cm, the number of oocytes recovered and the number of embryos which cleaved did not differ between the older and the younger women. However, conception rates were markedly lower in the older women than the overall pregnancy rate in the IVF programme during the same time period. We conclude that the older women in this study have a normal response to ovarian stimulation but may have a decreased receptivity of the endometrium or increased numbers of embryos with chromosomal abnormalities, leading to a reduced rate of implantation.

Some critical issues for a reliable molecular dynamics simulation of nano-machining

By using a molecular dynamics method, a computer simulation of a scratch test on bilayer thin films on a nanometer scale has been performed. In the present simulation, the substrate and thin-film material are TiN or SiO2 and Al or Cu, respectively. The indentor is assumed to be a perfect rigid body, and the Morse potential is utilized as the interaction between the indentor and a specimen atom. The extended Tersoff potential is assumed as the interaction between specimen atoms. Results indicate that the standard deviation of the friction constant becomes maximum when the scratching load is critical to spalling. The critical loads obtained by the present simulation and actual experiments do not match quantitatively. In contrast, the maximum standard deviation reproduces the spalling strength evaluated from actual experiments. On the basis of this finding, a new evaluation technique for adhesion strength using a nanoscratching test is proposed.

We have been looking at the properties of physical configurations that occur in nature in order to characterize, predict, and control network robustness in dynamic communication networks. Our framework is based on the definition of a potential energy function to characterize robustness in communication networks and the study of first- and second-order variations of the potential energy to provide prediction and control strategies for network-performance optimization. This paper describes novel investigations within this framework that draw from molecular system dynamics. The Morse potential, which governs the energy stored in bonds within molecules, is considered for the characterization of the potential energy of communication links in the presence of physical constraints such as the power available at the transmitters in a network. The inclusion of the Morse potential translates into improved control strategies, where forces on network nodes drive the release, retention, or reconfiguration of communication links based on their role within the network architecture. The performance of the proposed approach is measured in terms of the number of source-to-destination connections that have an end-to-end communications path. Simulation results show the effectiveness of our control mechanism, where the physical topology reorganizes tomaximize the number of source-to-destination communicating pairs. The algorithms developed are completely distributed, show constant time complexity and produce optimal solutions from local interactions, thus preserving the system's self-organizing capability.

In this study, MD simulations have been performed to observe the behavior of a grain boundary in an a-Fe plate under 2-dimensional loading. In MD simulation, the acceleration of every molecule can be achieved from the potential energy and the force interacting between each molecule, and the integration of the motion equation by using the Verlet method gives the displacement of each molecule. Initially, four α-Fe rectangular plates which have different misorientation angles of grain boundary were modeled by using the Johnson potential and Morse potential. We compared the potential energy of the grain boundary system with that of the perfect structure model, which does not have a grain boundary inside. Also, we could obtain the width of the grain boundary by investigating the local potential energy distribution. The tensile loading for each grain boundary model at room temperature was applied and the behavior of the grain boundary was studied. From this study it was clarified that when the Johnson potential is used, the obvious fracture mechanism occurs along the grain boundary. With the Morse potential, the diffusion of the grain boundary appears instead of the grain boundary fracture.