Papers by Keyword: Molecular Dynamic Simulation

Abstract: CdTe model containing 9955 atoms was built and simulated by the method of molecular dynamics (MD) with the Stillinger–Weber (SW) potential. The model was obtained by heating from 300K to 3000K at a rate of 10¹³ K/s. The structural properties of the model are investigated through the total energy per atom, the partial radial distribution functions (PRDFs), the coordination number distributions and the bond-angle distributions. Calculation results have shown that the model has a melting point of about 1370K and changes from tetrahedral to octahedral structure when the temperature of CdTe model is above the melting point. These results are consistent with the reported experimental and simulation results. In addition, the mobility of Cd and Te atoms is also researched through the mean squared displacement (MSD) and the diffusion coefficients of Cd and Te atoms.

Abstract: The structure of the two-dimensional BN containing 9941 atoms has been studied by classical molecular dynamics simulation with Tersoff potential. The periodic boundary condition is applied to the two x and y directions, while the z direction is free. The analysis results of the function of total energy per atom and heat capacity, mean squared displacement, diffusion coefficient, radial distribution function, distribution of coordination number, angle distribution, and ring statistics show that the melting point of the material is about 4600 K. This value is higher than the experimental value as well as the previous simulation results. The observations also show that the melting process begins at the corners and edges and then spreads across the face of the model. The breakage of the B-N bond leads to the formation of clusters of N₂ molecules and B with different sizes.

Abstract: In this work we used a combination of molecular dynamic simulation and statistical thermodynamic theory in order to obtain stability region of propane hydrates formed from sea water. MD simulation were used to get thermodynamic properties of liquid water phase, while statistical thermodynamic theory were applied for solid hydrate phase. We reconstructed phase equilibrium line ‘sea water – hydrate – gas’ and according to our calculations the temperature shift of this line is about 3^◦. Moreover, we have shown a possibility to obtain thermodynamic parameters of salt water directly from MD simulations with sufficient accuracy.

Abstract: We investigate the structural evolution of the single-walled carbon nanotubes (SWNTs) by molecular dynamics (MD) simulation using the Gao-Weber potential. The structural evolution of SWNTs is analyzed through the total energy per atom, the radial distribution function, coordination number, bond angle and the distribution of ring statistics. The results show that the melting temperature of SWNTs occurs at around T_m=5620 K. This value is in good agreement with the result of Zhang and co-workers. The visualization indicates that the initially perfect SWNTs is broken resulting in the ring of various.

Abstract: Aluminum-Iron-Silicon (Al-Fe-Si) alloys are extremely applied in many specific industries, such as aerospace and automobiles. Their atomic concentration influences the mechanical behavior of the investigated τ_4-Al₃Fe₂Si and τ_12-Al₃FeSi₂ phases. The uniaxial-tensile deformation is used to compare their structural evolution under the same conditions.Atomic displacement and mechanical behavior have an interest in the elastic and plastic areas. Stress-Strain responses and Radial Distribution Function (RDF) are required. Further, atomic simulations using molecular dynamics demonstrate the change occurs. Its process is carried out at a strain rate of 21×10¹⁰ s^-1 using the NPT (isothermal-isobaric) with roughly 20 700 atoms at a pressure of 10⁵ Pa. Furthermore, using a Nosée Hoover thermostat at the temperature of 300 k is decisive.The Modified Embedded Atoms Method (MEAM) is the applied potential between Al, Fe, and Si atoms. The elastic modulus and single pair atomic correlation before and after straining are increased by this method. The atomic correlations are shown in short- and long-range order and the τ₁₂-Al₃Fe₂Si phase illustrates stronger properties compared to τ_4-Al₃Fe₂Si phase. Our results underscore an important variation associated with the change of iron and silicon concentration. More specifics are covered in the selection paper.

Abstract: A molecular dynamic (MD) simulation, which is used for estimating mechanical properties of both microscopic and mesoscopic materials during loading/unloading processes. Understanding the deformation mechanisms of material's internal structure, shape and volume is a key step to enhance its strength and rigidity. Novel nanostructures, nanoparticles and nanocomposites, more efficient, selective, and environmental friendly can be developed and suggested. At the moment, few experimental methods can characterize molecular mechanisms due to their time-consuming and cost-intensive. Therefore, MD simulation allows to gain understanding in structure-to-function relationships involved in the low-dimensional materials. Specifically, MD simulation can be performed on the time scale of nanoseconds, and in three dimensions, it is thus sufficient for the study of the mechanical behaviors and deformation mechanisms at a molecular level. This work reviews the progress in MD simulation of the mechanical properties and structure deformations for various tubular nanomaterials including silicon, carbon and III-V compound nanotubes (NTs), respectively. In particular, we have a detailed description and analysis of the impacts of environmental and structural factors on material strength for the present nanostructures. It is hopeful that this review can provide certain reference for the follow-up research.

Abstract: Zirconia has a number of remarkable properties, including a very low thermal conductivity. In this research, the phonon thermal conductivity of two phases (cubic and monoclinic) of zirconia (ZrO₂) are calculated. For this purpose, an equilibrium molecular dynamics simulation employing the Green-Kubo formalism is used. The results are presented in detail over a wide temperature range, from 100 K to 2400 K and 100 K to 1400 K for the above-mentioned structures, respectively, with a 100K temperature step. The temperature dependence of the equilibrium atomic volume demonstrated a reasonable agreement with the experimental data. Moreover, the lattice thermal conductivity was calculated by analysing the heat current autocorrelation function. The results showed that zirconia has a low thermal conductivity that is dependent on the temperature. It was also shown that the lattice thermal conductivity of the two phases of zirconia can be decomposed into three contributions due to the acoustic shortrange and long-range phonon and optical phonon modes. Finally, the results from this research are compared with the available experimental data.

Abstract: In this work, we simulated and analysed phase transformations in the structure of nanosized bimetallic titanium-containing clusters during the cooling process. The results demonstrate the predominantly α+β crystalline structure of the TiAl nanoalloy after cooling, and the TiV nanoalloy has an amorphous structure. The glass transition temperatures for bimetallic systems TiAl and TiV for various compositions were determined.

Abstract: The paper is devoted to some properties of grain boundaries: Segregation and concentration phase transitions – two important consequences of atomic interactions in grain boundaries. Except of a short description the Gibbs method of surface excesses and grain boundary segregation isotherms with the limited number of segregation sites in grain boundary, the paper concentrates on the effects of complexes formation, including thermodynamic and computer modeling, and concentration phase transition in the grain boundaries in systems with restricted solubility and intermediate compounds.

Abstract: Carbamazepine (CBZ) is well known to have low solubility, hence an understanding of crystal behaviour is vital to improve the solubility of the drugs, hence for the oral bioavailability. The objectives of this work are to assess the morphology prediction of the most stable form of CBZ, which form (III) and to access the dissolution behaviour of the crystal. Material Studio 4.0 was used to predict the morphology of CBZ form (III) based on attachment energy calculations in vacuum condition by using the combination of MNDO charges from MOPAC with PCFF potential function. Later, predicted morphology was used for dissolution prediction in ethanol solvent using dynamic simulation with CVFF potential function. From the result, the morphology prediction of CBZ form (III) produced hexagonal – like shape with seven dominated facets; (011), (11-1), (100), (10-2), (020), (110) and (11-2) with the most morphological important is (011) face with 45.23% area while the fastest growing facet is (11-2) which only 0.91% area contributed to the whole crystal. The lattice energy calculated was -21.62 kcal/mol with only 1.36% error compared to the experimental value; -21.33 kcal/mol. The dissolution prediction result shows that small facet area with the amine and carbonyl groups exposed at the surface will dissolve readily than the other facets. This result explains that the small facet area with protruding functional groups that can form the hydrogen bond to ethanol molecules will be the most favourable facet to dissolve.