scholarly journals Local structure and distortions of mixed methane-carbon dioxide hydrates

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Bernadette R. Cladek ◽  
S. Michelle Everett ◽  
Marshall T. McDonnell ◽  
Matthew G. Tucker ◽  
David J. Keffer ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Exchange Process ◽  
Carbon Dioxide Sequestration ◽  
Distribution Functions ◽  
Atomic Scale ◽  
Mixed Gas ◽  
Pure Compounds ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Methane Carbon

AbstractA vast source of methane is found in gas hydrate deposits, which form naturally dispersed throughout ocean sediments and arctic permafrost. Methane may be obtained from hydrates by exchange with hydrocarbon byproduct carbon dioxide. It is imperative for the development of safe methane extraction and carbon dioxide sequestration to understand how methane and carbon dioxide co-occupy the same hydrate structure. Pair distribution functions (PDFs) provide atomic-scale structural insight into intermolecular interactions in methane and carbon dioxide hydrates. We present experimental neutron PDFs of methane, carbon dioxide and mixed methane-carbon dioxide hydrates at 10 K analyzed with complementing classical molecular dynamics simulations and Reverse Monte Carlo fitting. Mixed hydrate, which forms during the exchange process, is more locally disordered than methane or carbon dioxide hydrates. The behavior of mixed gas species cannot be interpolated from properties of pure compounds, and PDF measurements provide important understanding of how the guest composition impacts overall order in the hydrate structure.

Simulating Structural Transformation of a Cu1553 Nanoparticle on Heating at Atomic Scale

2015 ◽  
Vol 817 ◽  
pp. 736-739
Author(s):  
Jing Zhang ◽  
Peng Yu
Keyword(s):  
Structural Transformation ◽  
Structural Changes ◽  
Distribution Functions ◽  
Atomic Scale ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Different Temperatures ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Pair Analysis

By means of molecular dynamics simulations within the framework of embedded atom method, we observe the structural transformation of a Cu nanoparticle containing 1553 atoms at atomic scale on a heating series from 350K to 1200K at an increment of 50K. With increasing the temperature, the structural changes result in apparent increases in internal energy. Pair distribution functions (PDFs) and pair analysis (PA) technique as well as the atom packing at different temperatures are used to identify the local structural patterns during the melting of this particle.

scholarly journals Crystal growth of clathrate hydrates formed with methane + carbon dioxide mixed gas at the gas/liquid interface and in liquid water

2015 ◽  
Vol 39 (11) ◽  
pp. 8254-8262 ◽  
Author(s):  
Hiroki Ueno ◽  
Hotaka Akiba ◽  
Satoru Akatsu ◽  
Ryo Ohmura
Keyword(s):  
Carbon Dioxide ◽  
Crystal Growth ◽  
Liquid Water ◽  
Liquid Interface ◽  
Clathrate Hydrates ◽  
Mixed Gas ◽  
Hydrate Crystal ◽  
Methane Carbon

Observations of CH4 + CO2 hydrate crystal growth formed at the gas/liquid interface and in liquid water were made.

scholarly journals Bulk and interfacial properties of decane in the presence of carbon dioxide, methane, and their mixture

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Nilesh Choudhary ◽  
Arun Kumar Narayanan Nair ◽  
Mohd Fuad Anwari Che Ruslan ◽  
Shuyu Sun
Keyword(s):  
Carbon Dioxide ◽  
Oil Recovery ◽  
Carbon Capture ◽  
Theoretical Calculations ◽  
Carbon Capture And Storage ◽  
Interfacial Properties ◽  
Gradient Theory ◽  
Geological Conditions ◽  
Dynamics Simulations ◽  
Methane Carbon

AbstractMolecular dynamics simulations were performed to study the bulk and interfacial properties of methane + n-decane, carbon dioxide + n-decane, and methane + carbon dioxide + n-decane systems under geological conditions. In addition, theoretical calculations using the predictive Peng-Robinson equation of state and density gradient theory are carried out to compare with the simulation data. A key finding is the preferential dissolution in the decane-rich phase and adsorption at the interface for carbon dioxide from the methane/carbon dioxide mixture. In general, both the gas solubility and the swelling factor increase with increasing pressure and decreasing temperature. Interestingly, the methane solubility and the swelling of the methane + n-decane system are not strongly influenced by temperature. Our results also show that the presence of methane increases the interfacial tension (IFT) of the carbon dioxide + n-decane system. Typically, the IFT of the studied systems decreases with increasing pressure and temperature. The relatively higher surface excess of the carbon dioxide + n-decane system results in a steeper decrease in its IFT as a function of pressure. Such systematic investigations may help to understand the behavior of the carbon dioxide-oil system in the presence of impurities such as methane for the design and operation of carbon capture and storage and enhanced oil recovery processes.

Investigations using wide-angle electron diffraction on pair ordering mechanisms in FeTb alloys by thermal annealing

1994 ◽  
Vol 52 ◽  
pp. 660-661
Author(s):  
M. Tewes ◽  
J. Zweck ◽  
H. Hoffmann
Keyword(s):  
Electron Diffraction ◽  
Short Range ◽  
Local Density ◽  
Coordination Shell ◽  
Density Fluctuations ◽  
Distribution Functions ◽  
Atomic Scale ◽  
Short Range Ordering ◽  
Isotropic Structure ◽  
Pair Distribution Functions

In our recent work we have shown that electron diffraction is a suitable and precise method to observe short range ordering in various amorphous FeTb alloys by calculating pair distribution functions (PDFs) from these data by means of a fourier inversion. A PDF g(r) is an autocorrelation function of the specimen’s density fluctuations: g(r) = 4πr(ϱ(r) - ϱo) with ϱ(r): autocorrelation of the local density in a distance r, and ϱo macroscopic density of the specimen. The spatial resolution that can be achieved is better than 0.02 nm, and the fine structure of the first coordination shell of the short range order has been described quantitatively with an isotropic structure model. The deviation between calculated and measured PDFs has been about 2%.However, the origin of the uniaxial perpendicular anisotropy in rare earth / transition metal amorphous alloys like FeTb is in general attributed to small anisotropic concentration fluctuations on an atomic scale as introduced in pair ordering, band orientation or stress induced anisotropy models.

Molecular dynamics simulations of EPON-862/DETDA epoxy networks: structure, topology, elastic constants, and local dynamics

Soft Matter ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 721-733 ◽  
Author(s):  
Spyros V. Kallivokas ◽  
Aristotelis P. Sgouros ◽  
Doros N. Theodorou
Keyword(s):  
Molecular Dynamics ◽  
Elastic Constants ◽  
Distribution Functions ◽  
Glass Temperature ◽  
Segmental Dynamics ◽  
Structure Topology ◽  
Xrd Patterns ◽  
Dynamics Simulations ◽  
Networks Structure ◽  
Pair Distribution Functions

Partial pair distribution functions, XRD patterns, segmental dynamics, elastic constants and glass temperature in EPON862/DETDA epoxy predicted through molecular dynamics.

Pressure Induced Structural Transformations in Nanocluster Assembled Gallium Arsenide

1998 ◽  
Vol 536 ◽  
Author(s):  
S. Kodiyalam ◽  
A. Chatterjee ◽  
I. Ebbsjö ◽  
R. K. Kalia ◽  
H. Kikuchi ◽  
...  
Keyword(s):  
Bond Angle ◽  
Structural Phase ◽  
High Stress ◽  
Distribution Functions ◽  
Structural Phase Transformation ◽  
Spatially Resolved ◽  
Parallel Molecular Dynamics ◽  
Dynamics Simulations ◽  
Pair Distribution Functions ◽  
Single Cluster

AbstractPressure induced structural phase transformation in nanocluster assembled GaAs is studied using parallel molecular dynamics simulations in the isothermal-isobaric ensemble. In this system the spatial stress distribution is found to be inhomogeneous. As a result structural transformation initiates in the high stress regions at the interface between clusters. Structural and dynamical correlations in the nanophase system are characterized by calculating the spatially resolved bond angle and pair distribution functions and phonon density of states and comparing them with those for a single cluster and bulk crystalline and amorphous systems.

Structure, Fragmentation, and Phonons in Silicon Microclusters

1992 ◽  
Vol 293 ◽  
Author(s):  
Wei Li ◽  
Rajiv K. Kalia ◽  
Priya Vashishta
Keyword(s):  
Molecular Dynamics ◽  
Structural Information ◽  
Magic Number ◽  
Distribution Functions ◽  
Dynamics Simulation ◽  
Silicon Clusters ◽  
Atom Clusters ◽  
Densities Of States ◽  
Dynamics Simulations ◽  
Pair Distribution Functions

AbstractMolecular-dynamics simulations are performed to investigate structures, vibrational spectra, and fragmentation channels of silicon microclusters ranging in size from 32 to 52 atoms. Structural information is derived from pair-distribution functions, bond-angle distributions, and the structure and statistics of rings. Molecular-dynamics simulation results for energetics suggest that 33, 39, 45 and 51 atom clusters are highly stable. These magic-number clusters have predominantly five and six membered rings. With an increase in “temperature”, most clusters tend to fragment by loosing one atom at a time. Vibrational densities of states of 32-52 atom silicon clusters show only minor deviations from the bulk behavior.

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