Papers by Keyword: MD

Abstract: To clarify the effect of relative humidity on molecular chain’s network structure, we at first employ Molecular Dynamics (MD) method to constitute the computational model for Nafion membrane, in which the water channel is artificially reproduced with an aggregation of water molecules. And then, relaxation calculation is performed and a relatively stable microstructure of Nafion membrane is derived. It is found that the regions of relatively low density of molecular chain’s network appear interchangeably together with those of relatively high density of water molecules.

Abstract: For the purpose of studying the difference of mixing and cocrystallization of TNT(2,4,6-trinitrotoluene) and CL-20(2,4,6,8,10,12-hexanitrohexaazaisowurtzitane), molecular dynamics simulation(MD) was performed within Discover code. After the equilibrium of the system, the average bond length of trigger bond(Lave) is almost unchanged after mixing or cocrystallization. However, the largest bond length of trigger bond(Lmax) of CL-20 in cocrystal is shorter than that of it in pure CL-20, indicting the cocrystal is more difficult to be detonated than CL-20. The Lmax of TNT shows the same result. The cocrystal shows a larger cohesive energy density than composite ones, suggesting the cocrystal is more insensitive. Besides, trigger bond energy of cocrystal is larger than physical mixture of TNT and CL-20, suggesting the cocrystal is more insensitive. The mechanical properties show the cocrystal is more harder than pure TNT or CL-20, but has a weaker ductibility and tenacity.

Abstract: An improvement is made on the adaptive step size of the gradient Descent (GD). We propose that the improved GD can be used in Molecular Dynamics (MD) to determine the shortest distance between an irregular curve (described in high-order equation) and a point outside the curve, that we show that it can solve the problem with affordable computational power and high accuracy (an average of 1% error in around 30 iterations).

Abstract: Electrochemical Discharge micro-machining process appears better utility with greater effectiveness in the modern micro-machining industrial field. Electrochemical discharge micro-machining process is involved to generate micro-channel as well as curve profile on glass for utilization as micro-fluidic device. This paper shows second order mathematical modeling of correlation between the machining criteria such as machining rate as a form of material removal rate (MRR), overcut (OC), machining depth (MD) with various process parameters like applied voltage (V), electrolyte concentration (wt %) and inter-electrode gap (IEG) (mm). The analysis of variance (ANOVA) has been performed to find out the adequacy of the developed models.This paper also shows the multi objective optimization to achieve the optimal parametric combination for maximum MRR, MD and minimum OC using response surface methodology (RSM). Keywords: μ-ECDM, MRR, OC, MD, RSM, ANOVA, Glass.

Abstract: To understand the capture of charged polymer in salt solution, we investigated the effect of the temperature, concentration of DNA molecules and electrical field to the polynucleotide capture rate by using a single graphene nanopore. From the result of the molecular dynamics simulations, it suggested that the capture rate becomes higher with increasing temperature and that it increases exponentially with the electrical field, and that low and high concentration of the polymer do not exhibit optimal capture rate. By analyzing the simulations results we predict that the capture rate is related to the aperture and the structure of the pore.

Abstract: Computer simulation techniques in atom scale have now become so powerful that phenomena associated with irradiation damage effects in metals can be modelled with a high degree of realism. As a powerful tool, molecular dynamics (MD) is applied to study the displacement cascades initiated by the neutrons when they interact with matter. There exist a lot of inter-atomic potentials dedicated to bcc Fe and we choose the EAM potential. At first time PKAs (Primary knock-on atoms) knocked on a atom and send a part of energy to it what result displacement cascades. After about several ps, a lot of atoms are knocked to leave the equilibrium position and became self- interstitial atoms (SIAs). A lot of equilibrium position became vacancies. Some SIAs and vacancies form dumb-bells structure. Several vacancies or SIAs assembled the clusters. In other papers we haven’t found about the SIAs and vacancies can be assembled the SFT-like clusters in bcc Fe. In our study, we occasionally find SIAs can assemble to form the cluster in bcc Fe but need a higher energy. In our study, we choose the temperature from 100K to 600K, the energy from 100eV to 20keV. The particles scale is about 300 thousands. In a series of experimentation we find that as the temperature increase as the number of the SIAs and vacancies increase too. By the same token, as the energy increase we will find the same result.

Abstract: Molecular dynamics (MD) simulations of nanometric scratching with diamond tip are conducted on single crystal copper crystal plane (010), and MD simulations are carried out to investigate the mechanism of material removal and the generation of defects on the surface, subsurface and inner of material. During the process of diamond tip scratching the surface of single crystal copper on conditions of different scratching speeds, depths and widths. We achieved the forming details of the chip. While the generation and moving process of defects, such as dislocation, are recorded. The different times of atomic displacement and interaction force are also shown through MD simulation. The evolvement of the lattice pattern in the abrasive processes are analysed by radial distribution function (RDF) and computing the changes of workpiece’s atomic displaces and forces. At the same time, the lattice reconfiguration and the onset and the evolvement process of defects and are analysed by RDF and atomic perspective method, respectively. The simulation results show that scratching speed play role in the course of the form of removing chips, and that different scratching widths and depths of tool have effect on onset and evolvement of lattice defects of workpiece in abrasive processes. This study can give more fundamental understanding of nanosconstruction from atomistic motions and contribute to the design, manufacture and manipulation of nano-devices

Abstract: NIL(Nano Imprint Lithography) is one of the most promising lithography techniques. There are many variants of NIL, and two major techniques of them are thermal NIL and UV NIL. Here, we focus ourselves on the thermal NIL. During the thermal NIL, the polymeric patterns experience large mechanical strain and high temperature, and this often leads to malformation of polymeric patterns. So it is needed to improve the pattern fidelity and contrast, and these are believed to be closely related to the process condition and mechanical properties. In thermal NIL, PMMA is widely used and chosen as target polymer. Generally, mechanical properties in nano scale are really hard to acquire. In this study, we estimate the mechanical properties of PMMA by molecular dynamic simulation. These properties will be used as input of continuum simulation. We will estimate stress-strain relationship of PMMA. This stress-strain relationship depends on strain rate and temperature. So we will study about strain rate and temperature effect.

Abstract: The interactions of a dislocation with commonly observed irradiation induced defects such as a stacking fault tetrahedron (SFT) and a void are studied using molecular dynamics (MD) simulation methods. The simulation of an SFT interacting with a dislocation in face centered cubic (FCC) copper (Cu) reveals that an SFT is a strong obstacle against a dislocation motion, with dislocation detachment often involving an Orowan like mechanism. The resulting SFT generally involves a shear step, although partial absorption is also observed in some specific interaction geometries. Dislocation interaction with a void has been studied in body centered cubic (BCC) molybdenum (Mo). The dislocation locally annihilates upon contact with the void and then re-nucleates on the void surface as the dislocation glides past the void. The interaction results in the simple shear of the void by one Burger’s vector. The obstacle strength of the void is measured using conjugate gradient molecular statics (MS) method as a function of void size. A large increase in the obstacle strength is observed for a void size greater than 3 nm in diameter.

Abstract: The slider geometry has a great influence on tribological behaviors for nanoscale sliding systems. The present study employs the finite element method (FEM) atomic approach to investigate the friction behaviors for rectangular slider and triangular slider on slab. The current investigation chooses diamond-like carbon as the hard material, and copper as the soft material. The atomic configurations following sliding under non-interactive, attractive, and repulsive force field are observed for sliding system. The relationships between the normal force, the friction force, and the sliding distance are discussed. The present results are in good agreement with those of previous studies using molecular dynamics (MD) simulation.