Papers by Keyword: Molecular Dynamics Simulation

Abstract: Molecular dynamics simulations are used to study the dissociation inhibiting mechanism of lecithin for structure I hydrates. Adsorption characteristics of lecithin and PVP (poly (N-vinylpyrrolidine)) on the hydrate surfaces were performed in the NVT ensemble at temperatures of 277K and the hydrate dissociation process were simulated in the NPT ensemble at same temperature. The results show that hydrate surfaces with lecithin is more stable than the ones with PVP for the lower potential energy. The conformation of lecithin changes constantly after the balanced state is reached while the PVP molecular dose not. Lecithin molecule has interaction with lecithin nearby and hydrocarbon-chains of lecithin molecules will form a network to prevent the diffusion of water and methane molecules, which will narrow the available space for hydrate methane and water movement. Compared with PVP-hydrate simulation, analysis results (snapshots and mass density profile) of the dissociation simulations show that lecithin-hydrate dissociates more slowly.

Abstract: The spatial packing modes of organic hole transporting materials exert a significant effect on the charge mobility. However it is difficult to reasonably design the materials with high-charge transfer performances due to the limits of the data regarding crystal structures. In this work, molecular dynamics simulation was used to find the new spatial packing ways of organic photoelectric materials containing oligothiophene based on randomly distributed initial structures. This work lays a theoretical foundation for designing favorable organic carrier transporting materials.

Abstract: The molecular dynamics simulations with embedded atom model (EAM) potential had performed to investigate the icosahedral network connectivity in Mg₇₀Zn₃₀ alloy. The microstructure was detected with a new precise method of largest standard cluster analysis. It was validated that the EAM potential is succeed in reflecting the objective physical nature of Mg-Zn alloy systems. Results shows that large amount of nanoclusters consist of ICOIs, which shows large connectivity variations, formed in the system with decreasing temperature. And the ICOIs connect over extended range act as backbone for a networked structure.

Abstract: To explore effects of air humidity on properties of JO-9159 explosive, the amorphous model of six components was constructed by Materials Studio software, periodic molecular dynamics simulation was conducted at seven kinds of relative humidity ranging from 10% to 70% for (001), (010), (100) crystal planes of JO-9159 explosive in COMPASS force field and NVT ensemble. Mechanical properties, sensitivity and detonation properties of JO-9159 explosive were researched basing on equilibrium trajectory of model. The results show that with the increasing of relative humidity, the total adsorption energy increases. The adsorption capacity of JO-9159 explosive for H₂O is much stronger than O₂ and N₂; The breaking strength has a decreasing trend with the humidity increases and the stiffness and hardness of JO-9159 explosive are smaller at 30% and 40% relative humidity; At 30% relative humidity, the sensitivity of JO-9159 explosive is highest and detonation properties are weakest, while the detonation properties are strongest at 20% relative humidity.

Abstract: In this study, mass transport properties of liquid Cu-Ag alloys are investigated over wide temperature and composition ranges. The calculations are performed within the framework of the Green-Kubo (GK) formalism by using equilibrium molecular dynamics (MD) simulations along with one of the most reliable embedded-atom method potentials for this system developed by [P. Williams et al.: Modell. Simul. Mater. Sci. Eng. vol. 14 (2006), p. 817]. The approach employed allows for evaluation of the components’ self-diffusion coefficients as well as the phenomenological coefficient for mass transport Lcc. The results obtained in this study can be used to predict the kinetics of solidification of real liquid Cu-Ag alloys.

Abstract: Owing to the extremely rapid tool wear, ultra-precision manufacturing of mold steel through single point diamond turning (SPDT) operation becomes a challenging task. Molecular dynamics (MD) simulation is an appropriate tool to study nanoscale processes occurring at the femtosecond/picosecond timescale. The wear mechanism of the diamond tool is discussed by means of molecular dynamics in which atomic position variation, temperature fluctuations were involved. According to the analysis results, iron atoms have unpaired d electrons, these iron atoms may connect with diamond carbon atoms through chemical bonds which are the driving force to the diamond removal and making diamond convert into graphite. The simulation results demonstrated that, it is possible to mitigate the wear of diamond tools effectively, if those bindings between unpaired d electrons and diamond carbon atoms of the tool can be under control.

Abstract: The interface of the ternary boride hard cladding material consists of hard phase (Mo₂FeB₂) and bonding phase (α-Fe). In this paper, on the basis of the ideal interface model of Mo₂FeB₂ (100)/α-Fe (001) built with the molecular dynamics software, the Mo₂FeB₂ (100)/α-Fe (001) interface models with micro-cracks parallel with the interface, normal to the interface, and inclined to the interface have been built separately. The interface bonding energies of these four different interface models have been calculated, which shows that the interface model with the micro crack inclined to the interface has the biggest interface bonding energy, while the interface model with the micro crack parallel with the interface has the smallest bonding energy, the interface crack will be the most easily to propagate. The change rule of bonding energy of the interface model with the micro crack parallel with the interface with different lengths has been simulated and analyzed.

Abstract: Water confined in carbon nanotubes (CNTs) under the influence of an electric field has interesting properties that are potential for nanofluidic-based applications. With molecular dynamics simulations, this work shows that the electric field induces formation of ordered structures of water molecules in the CNTs. Formation of the ordered structures strengthens the electrostatic interaction between the water molecules. As a result, water strongly prefers to fill CNTs over methanol and it produces a separation effect. Interestingly, the separation effect with the electric field does not decrease for a wide range of CNT diameter.

Abstract: The 4H-SiC(000-1)_C and (0001)_Si surface reconstructed structures and the oxidation processes of these surfaces are investigated using a first-principles calculation method. The most stable reconstructed 4H-SiC(000-1)_C and (0001)_Si surfaces have p-bonded chains. In the topmost SiC bilayer, half of Si and C atoms exchange their positions and C-C or Si-Si bonds formed densely below the surfaces. When we place a SiO₂ layer on the p-bonded chain (000-1)_C surface, C-C bonds are formed more densely below the interface. We simulate a sequence of O₂ molecules arrivals at an interface of tridymite-phase-SiO₂ and 4H-SiC(000-1)_C. Dissociated O atoms at the interface tended to make bonds with Si atoms. The C-C bonds in the SiC substrate break easily and a local C surface occasionally appears. We have examined how the surface structure changes through an O₂ molecule exposure by using a classical molecular dynamics simulation program and confirmed the formation of C-C bonds below the surface and the interface.

Abstract: We report the results of a simulation study of the mechanical deformation of NiAl nanowires constrained in Al metal matrix. The constrained nanowires showed high elastic yield stress and nonelastic stretching via a transition from the B2 to BCT phase. The phase transformation mechanism was that of atomic shuffling, via the appearance, spreading, and aggregation of isolated defect atoms, instead of dislocation movement. Because of geometry constraints, the interphase energy between the new and parent phases is not readily released, which results in strain hardening.