Self-diffusion coefficients of methane/n-hexane mixtures at high pressures: An evaluation of the finite-size effect and a comparison of force fields

2020 ◽  
Vol 155 ◽  
pp. 104639 ◽  
Author(s):  
Thiago J.P. dos Santos ◽  
Charlles R.A. Abreu ◽  
Bruno A.C. Horta ◽  
Frederico W. Tavares
Keyword(s):  
Size Effect ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Force Fields ◽  
Finite Size ◽  
Finite Size Effect ◽  
Self Diffusion

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.

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.

scholarly journals Finite size effect on Dissociation and Diffusion of chiral partners in Nambu-Jona-Lasinio model

2021 ◽  
Author(s):  
Paramita Deb ◽  
Sabyasachi Ghosh ◽  
Jai Prakash ◽  
Santosh Kumar Das ◽  
Raghava Varma
Keyword(s):  
Size Effect ◽  
Chiral Symmetry ◽  
Diffusion Coefficients ◽  
Finite Size ◽  
Finite Size Effect ◽  
Detailed Structure ◽  
Different Temperatures ◽  
The Masses ◽  
Sigma Meson ◽  
And Diffusion

Abstract The masses of pion and sigma meson modes, along with their dissociation in the quark medium, provide detailed spectral structures of the chiral partners. One has seen collectivity in pA and pp systems both at LHC and RHIC. In this article, we study the restoration of chiral symmetry by investigating the finite size effect on the detailed structure of the chiral partners in the framework of the Nambu-Jona-Lasinio model. Their diffusions and conductions have been studied through this dissociation mechanism. It is found that the masses, widths, diffusion coefficients, conductivities of chiral partners merge at different temperatures in the restoration phase of chiral symmetry. However, merging points are shifted to lower temperatures when one introduces the finite size effect into the picture. The strengths of diffusions and conductions are also reduced once the finite size is introduced in the calculations.

scholarly journals Fick Diffusion Coefficients via Molecular Dynamics: An Alternative Approach in the Fourier Domain

2020 ◽  
Author(s):  
Thiago José Pinheiro dos Santos ◽  
Frederico W. Tavares ◽  
Charlles Abreu
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Finite Size ◽  
Correlation Method ◽  
Finite Size Effect ◽  
New Approach ◽  
Molecular Systems ◽  
Alternative Approach ◽  
Wide Range

Mutual diffusion coefficient data are required for several systems of scientific and engineering interest to properly describe mass transport phenomena over a wide range of pressures, temperatures, and compositions. In this work, we calculated Fick diffusion coefficients for some CO2+n-alkane mixtures at high pressures using a new method, which we derived by introducing modifications to the Fourier Correlation Method (FCM) originally proposed by Nichols and Wheeler [I&EC Research, 54, 12156–12164 (2015)]. The modified FCM (mFCM) results were validated through comparisons with experimental data and with Fick coefficients calculated by employing well-established Molecular Dynamics methodologies. The new approach has some interesting advantages, such as providing Fick coefficients for molecular systems directly through a single equilibrium calculation, in contrast to traditional methods in which an extra calculation is needed to obtain the so-called thermodynamic factor. It is shown that the new approach considerably reduces the finite-size effect of the simulation box on the calculated diffusion coefficients, which are thus obtained in the thermodynamic limit.<br>

scholarly journals Fick Diffusion Coefficients via Molecular Dynamics: An Alternative Approach in the Fourier Domain

2020 ◽  
Author(s):  
Thiago José Pinheiro dos Santos ◽  
Frederico W. Tavares ◽  
Charlles Abreu
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
High Pressures ◽  
Finite Size ◽  
Correlation Method ◽  
Finite Size Effect ◽  
New Approach ◽  
Molecular Systems ◽  
Alternative Approach ◽  
Wide Range

Mutual diffusion coefficient data are required for several systems of scientific and engineering interest to properly describe mass transport phenomena over a wide range of pressures, temperatures, and compositions. In this work, we calculated Fick diffusion coefficients for some CO2+n-alkane mixtures at high pressures using a new method, which we derived by introducing modifications to the Fourier Correlation Method (FCM) originally proposed by Nichols and Wheeler [I&EC Research, 54, 12156–12164 (2015)]. The modified FCM (mFCM) results were validated through comparisons with experimental data and with Fick coefficients calculated by employing well-established Molecular Dynamics methodologies. The new approach has some interesting advantages, such as providing Fick coefficients for molecular systems directly through a single equilibrium calculation, in contrast to traditional methods in which an extra calculation is needed to obtain the so-called thermodynamic factor. It is shown that the new approach considerably reduces the finite-size effect of the simulation box on the calculated diffusion coefficients, which are thus obtained in the thermodynamic limit.<br>

scholarly journals Theoretical Investigation of the Size Effect on the Oxygen Adsorption Energy of Coinage Metal Nanoparticles

2021 ◽  
Author(s):  
Amir H. Hakimioun ◽  
Elisabeth M. Dietze ◽  
Bart D. Vandegehuchte ◽  
Daniel Curulla-Ferre ◽  
Lennart Joos ◽  
...  
Keyword(s):  
Particle Size ◽  
Size Effect ◽  
Adsorption Energy ◽  
Single Point ◽  
Finite Size ◽  
Geometry Optimization ◽  
Oxygen Adsorption ◽  
Finite Size Effect ◽  
Full Geometry Optimization ◽  
Coinage Metal

AbstractThis study evaluates the finite size effect on the oxygen adsorption energy of coinage metal (Cu, Ag and Au) cuboctahedral nanoparticles in the size range of 13 to 1415 atoms (0.7–3.5 nm in diameter). Trends in particle size effects are well described with single point calculations, in which the metal atoms are frozen in their bulk position and the oxygen atom is added in a location determined from periodic surface calculations. This is shown explicitly for Cu nanoparticles, for which full geometry optimization only leads to a constant offset between relaxed and unrelaxed adsorption energies that is independent of particle size. With increasing cluster size, the adsorption energy converges systematically to the limit of the (211) extended surface. The 55-atomic cluster is an outlier for all of the coinage metals and all three materials show similar behavior with respect to particle size. Graphic Abstract

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