Molecular Dynamics Studies of Polymorphism of SiO2 at High Pressures: A Possible New Cubic Polymorph with High Density

1988 ◽  
pp. 129-140 ◽  
Author(s):  
Yoshito Matsui ◽  
Masanori Matsui
Keyword(s):  
Molecular Dynamics ◽  
High Pressures ◽  
High Density

Modeling the molecular dynamics of liquid metals at high pressures: Liquid potassium

2011 ◽  
Vol 85 (11) ◽  
pp. 1908-1916 ◽  
Author(s):  
D. K. Belashchenko ◽  
D. E. Smirnova
Keyword(s):  
Molecular Dynamics ◽  
High Pressures ◽  
Liquid Metals

Molecular Dynamics Simulations on Melting of Aluminum

2013 ◽  
Vol 423-426 ◽  
pp. 935-938 ◽  
Author(s):  
Ji Feng Li ◽  
Xiao Ping Zhao ◽  
Jian Liu
Keyword(s):  
Molecular Dynamics ◽  
Melting Point ◽  
Molecular Dynamics Simulations ◽  
High Pressures ◽  
Ambient Pressure ◽  
Initial Porosity ◽  
Equilibrium Melting Point ◽  
Porosity Effect ◽  
Dynamics Simulations ◽  
Experimental Melting Point

Molecular dynamics simulations were performed to calculate the melting points of perfect crystalline aluminum to high pressures. Under ambientpressure, there exhibits about 20% superheating before melting compared to the experimental melting point. Under high pressures, thecalculated melting temperature increases with the pressure but at a decreasing rate, which agrees well with the Simon's melting equation. Porosity effect was also studied for aluminum crystals with various initial porosity at ambient pressure, which shows that the equilibrium melting point decreases with the initial porosity as experiments expect.

scholarly journals Effects of temperatures on pressure-induced structural changes in amorphous Si: A molecular-dynamics study

10.29007/6kp3 ◽  
2020 ◽  
Author(s):  
Renji Mukuno ◽  
Manabu Ishimaru
Keyword(s):  
Molecular Dynamics ◽  
Phase Transformation ◽  
Amorphous Phase ◽  
Structural Changes ◽  
Interatomic Potential ◽  
Activation Barrier ◽  
Distribution Functions ◽  
High Density ◽  
Angle Distribution ◽  
Dynamics Simulations

The structural changes of amorphous silicon (a-Si) under compressive pressure were examined by molecular-dynamics simulations using the Tersoff interatomic potential. a-Si prepared by melt-quenching methods was pressurized up to 30 GPa under different temperatures (300K and 500K). The density of a-Si increased from 2.26 to 3.24 g/cm3 with pressure, suggesting the occurrence of the low-density to high-density amorphous phase transformation. This phase transformation occurred at the lower pressure with increasing the temperature because the activation barrier for amorphous-to-amorphous phase transformation could be exceeded by thermal energy. The coordination number increased with pressure and time, and it was saturated at different values depending on the pressure. This suggested the existence of different metastable atomic configurations in a-Si. Atomic pair-distribution functions and bond-angle distribution functions suggested that the short-range ordered structure of high-density a-Si is similar to the structure of the high-pressure phase of crystalline Si (β-tin and Imma structures).

scholarly journals Self-Diffusion Coefficients of Methane/n-Hexane Mixtures at High Pressures: An Evaluation of the Finite-Size Effect and a Comparison of Force Fields

2019 ◽  
Author(s):  
Thiago José Pinheiro dos Santos ◽  
Charlles Abreu ◽  
Bruno Horta ◽  
Frederico W. Tavares
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Force Fields ◽  
Transport Coefficients ◽  
Finite Size ◽  
Finite Size Effect ◽  
Self Diffusion ◽  
Analytical Correction ◽  
Dynamics Simulations

Mass transport coefficients play an important role in process design and in compositional grading of oil reservoirs. As experimental measurements of these properties can be costly and hazardous, Molecular Dynamics simulations emerge as an alternative approach. In this work, we used Molecular Dynamics to calculate the self-diffusion coefficients of methane/n-hexane mixtures at different conditions, in both liquid and supercritical phases. We evaluated how the finite box size and the choice of the force field affect the calculated properties at high pressures. Results show a strong dependency between self-diffusion and the simulation box size. The Yeh-Hummer analytical correction [J. Phys. Chem. B, 108, 15873 (2004)] can attenuate this effect, but sometimes makes the results depart from experimental data due to issues concerning the force fields. We have also found that different all-atom and united-atom models can produce biased results due to caging effects and to different dihedral configurations of the n-alkane.

The properties and behaviour of mantle minerals: a computer-simulation approach

1989 ◽  
Vol 328 (1599) ◽  
pp. 391-407 ◽  
Keyword(s):  
Mantle Convection ◽  
High Pressures ◽  
Magnesium Silicate ◽  
High Density ◽  
Lattice Simulation ◽  
Rigid Barrier ◽  
Mantle Minerals ◽  
Perfect Lattice ◽  
Direct Study ◽  
Spectroscopic Characteristics

The direct study of the majority of the physical properties of mantle-forming phases is currently beyond the limits of technology, because of the high pressures and temperatures (greater than 25 GPa and 1800 K) required to simulate lower-mantle conditions. As an alternative to direct study therefore, theoretical and computerbased techniques of lattice simulation and molecular dynamics have been employed to obtain an understanding of the behaviour of high-density silicates. The properties of perfect high-density silicate crystals, including their elastic and spectroscopic characteristics, have been investigated, but to date computer simulations of perfect lattice properties are insufficiently accurate to be used to solve geophysical problems. In contrast, the simulation of phase relations and defects properties are very successful. Small, negative Clapeyron slopes for perovskite-forming transformations are predicted, suggesting that the 670 km discontinuity may not be a rigid barrier to mantle convection. In addition, the activation energies for diffusion in forsterite and perovskite have been calculated, and the suggested high-temperature superionic conductivity of magnesium silicate perovskite has been confirmed.

MD Analysis of Effect of Relative Humidity on Molecular Chain’s Network Structure of PEM

2016 ◽  
Vol 725 ◽  
pp. 238-242
Author(s):  
Isamu Riku ◽  
Keisuke Kawanishi ◽  
Koji Mimura
Keyword(s):  
Molecular Dynamics ◽  
Relative Humidity ◽  
Computational Model ◽  
Network Structure ◽  
Water Channel ◽  
High Density ◽  
Nafion Membrane ◽  
Water Molecules ◽  
Low Density ◽  
Density Of Water

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.

Structural properties and defects of GaN crystals grown at ultra-high pressures: A molecular dynamics simulation

2018 ◽  
Vol 113 ◽  
pp. 644-649
Author(s):  
Tinghong Gao ◽  
Yidan Li ◽  
Quan Xie ◽  
Zean Tian ◽  
Qian Chen ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Structural Properties ◽  
High Pressures ◽  
Dynamics Simulation
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