Molecular simulations of supercritical fluid systems

Stubbs, John M.

doi:10.1016/j.supflu.2015.10.027

Cited by 62 publications

(24 citation statements)

References 425 publications

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“…Extensive investigations have been done on the dynamic crossover of supercritical phases of water [10,16], Iron [17], CO 2 [10,18,19], Argon [13,15], CH 4 [10] etc. In a recent review article, J.M.Stubbs covers a wide range of molecular simulation studies of supercritical fluids (SCF) [20]. Transport and structural behaviour of normal fluids under confinement has been of interest within the physics community due to their unusual properties with respect to the bulk fluid systems.…”

Section: Introductionmentioning

confidence: 99%

Structural behavior of supercritical fluids under confinement

Ghosh

Krishnamurthy

2018

Phys. Rev. E

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The existence of the Frenkel line in the supercritical regime of a Lennard-Jones (LJ) fluid shown through molecular dynamics (MD) simulations initially and later corroborated by experiments on argon opens up possibilities of understanding the structure and dynamics of supercritical fluids in general and of the Frenkel line in particular. The location of the Frenkel line, which demarcates two distinct physical states, liquidlike and gaslike within the supercritical regime, has been established through MD simulations of the velocity autocorrelation (VACF) and radial distribution function (RDF). We, in this article, explore the changes in the structural features of supercritical LJ fluid under partial confinement using atomistic walls. The study is carried out across the Frenkel line through a series of MD simulations considering a set of thermodynamics states in the supercritical regime (P=5000 bar, 240K≤T≤1500K) of argon well above the critical point. Confinement is partial, with atomistic walls located normal to z and extending to "infinity" along the x and y directions. In the "liquidlike" regime of the supercritical phase, particles are found to be distributed in distinct layers along the z axis with layer spacing less than one atomic diameter and the lateral RDF showing amorphous-like structure for specific spacings (packing frustration) and non-amorphous-like structure for other spacings. Increasing the rigidity of the atomistic walls is found to lead to stronger layering and increased structural order. For confinement with reflective walls, layers are found to form with one atomic diameter spacing and the lateral RDF showing close-packed structure for the smaller confinements. Translational order parameter and excess entropy assessment confirms the ordering taking place for atomistic wall and reflective wall confinements. In the "gaslike" regime of the supercritical phase, particle distribution along the spacing and the lateral RDF exhibit features not significantly different from that due to normal gas regime. The heterogeneity across the Frenkel line, found to be present both in bulk and confined systems, might cause the breakdown of the universal scaling between structure and dynamics of fluids necessitating the determination of a unique relationship between them.

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Section: Introductionmentioning

confidence: 99%

Structural behavior of supercritical fluids under confinement

Ghosh

Krishnamurthy

2018

Phys. Rev. E

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“…1 Abbreviations: SCW: Supercritical Water, HB: Hydrogen Bonding, MD: Molecular Dynamics, rdf: radial distribution function, LDA: Local Density Augmentation Molecular simulation has become a very important tool to investigate the properties of supercritical fluids and their solutions, as pointed out in recent reviews [46]. The present study has been therefore devoted to a more thorough investigation of this interplay by performing a series of molecular dynamics simulations of SCW along a near critical isotherm, aiming to shed light on open questions regarding the interrelation between hydrogen bonding, local density inhomogeneities and structural order in SCW.…”

Section: Introductionmentioning

confidence: 99%

Local structural fluctuations, hydrogen bonding and structural transitions in supercritical water

Skarmoutsos

Guàrdia

Samios

2017

The Journal of Supercritical Fluids

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The contribution of hydrogen bonding interactions to the formation of local density inhomogeneities in supercritical water at near-critical conditions has been extensively studied by means of molecular dynamics simulations. The results obtained have revealed the strong effect of water molecules forming one and two hydrogen bonds on the determination of the local density augmentation in the fluid. The local structural order has also been studied in terms of the trigonal and tetrahedral order parameters, revealing the correlation between local orientational order and hydrogen bonding. The dynamics of the structural order parameters exhibit similarities with local density ones. The local structural analysis performed in terms of nearest neighbors around the individual molecules provides additional significant evidence about the existence of a liquid-like to gas-like structural transition in supercritical water at the density range close to 0.2 ¿c, further supporting previous suggestions based on the interpretation of experimental thermodynamic data.Postprint (author's final draft

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“…Nevertheless, a significant clarification of this picture has gradually emerged over the last 15-20 years due to the concerted efforts of many experimental [7][8][9][10][11][12][13][14][15][16][17] and computational molecular modeling [18][19][20][21][22][23][24][25][26][27] research groups.…”

Section: Introductionmentioning

confidence: 99%

Universality of hydrogen bond distributions in liquid and supercritical water

Kalinichev

2017

Journal of Molecular Liquids

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International audienceMonte Carlo and molecular dynamics computer simulations using the rigid TIP4P and the flexible BJH intermolecular H2O potentials were carried out for 50 states of supercritical water characterizing a very wide range of thermodynamic conditions, 573 < T < 1273 K; 0.02 < rho < 1.67 g/cm3; 10 < P < 10,000 MPa. Good agreement with available experimental data of the simulated thermodynamic and structural properties give confidence to the quantitative statistical analysis of intermolecular hydrogen bonding under the conditions studied. Energetic, geometric, and angular characteristics of supercritical H-bonds and their distributions at a given temperature remain almost invariant over the entire density range studied from dilute gas-like (~ 0.03 g/cm3) to highly compressed liquid-like (~ 1.5 g/cm3) states. The increase of temperature from ambient to supercritical affects the characteristics of H-bonding in water much more dramatically than the changes in density along any supercritical isotherm. Compared to H-bonds in liquid water under ambient conditions, the H-bonds at 773 K are, on average, 10% weaker, 5% longer, and less linear. Both above and below the H-bonding percolation threshold the fractions of H2O molecules involved in a certain number of H-bonds in liquid and supercritical water closely follow the universal binomial distribution as a function of the average number of H-bonds per one water molecule in the system, as predicted by the independent bond theory. This universal distribution remains intact even when dynamic criteria of H-bonding lifetimes are additionally applied

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Molecular simulations of supercritical fluid systems

Cited by 62 publications

References 425 publications

Structural behavior of supercritical fluids under confinement

Structural behavior of supercritical fluids under confinement

Local structural fluctuations, hydrogen bonding and structural transitions in supercritical water

Universality of hydrogen bond distributions in liquid and supercritical water

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