Linear and nonlinear density response functions for a simple atomic fluid

Dalton, Benjamin A.; Glavatskiy, Kirill; Daivis, Peter J.; Todd, B. D.; Snook, Ian K.

doi:10.1063/1.4816514

Cited by 13 publications

(41 citation statements)

References 24 publications

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“…The SLF produces static average density perturbations in a fluid. We have described the density response of a fluid due to the SLF in detail in a recent publication [26]. The force is intentionally chosen to be in the y direction so that we can produce inhomogeneous density profiles that vary in the same direction that the velocity profiles vary.…”

Section: A Properties Of the Stf-slf Fluidmentioning

confidence: 99%

“…The SLF is also a sinusoidal function but the SLF-induced density profile is cosinusoidal. The potential energy field associated with the conservative SLF is, however, cosinusoidal, which explains why the density profile is cosinusoidal [26].…”

Section: A Properties Of the Stf-slf Fluidmentioning

confidence: 99%

“…(19). The methods for calculating the Fourier coefficients of the velocity and temperature series and the density series have been described in detail in previous publications [23,26]. For the streaming velocity series coefficients, a system of linear equations is constructed by minimizing the sum of the squares of the differences between the instantaneous x direction total velocities of each atom and a proposed general sine series as a function of each atom's y position.…”

Section: B Equations Of Motion For the Stf-slf Systemmentioning

confidence: 99%

“…1. For large field strength SLF, higher-order cosinusoidal harmonics are excited in the density profile [26]. In order to investigate the effects of density inhomogeneities in shear flow we might wish to apply single cosine component density perturbations.…”

Section: B Combined Stf-slf: Long Wavelength Density Perturbationsmentioning

confidence: 99%

“…In addition to the STF we implement a sinusoidal longitudinal force (SLF). In a recent publication we used the SLF method to investigate the linear and nonlinear density response functions for simple atomic fluids [26]. We developed a method for systematically perturbing fluid densities and measuring the Fourier components of the inhomogeneous density profiles.…”

Section: Introductionmentioning

confidence: 99%

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Effects of nanoscale density inhomogeneities on shearing fluids

et al. 2013

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It is well known that density inhomogeneities at the solid-liquid interface can have a strong effect on the velocity profile of a nanoconfined fluid in planar Poiseuille flow. However, it is difficult to control the density inhomogeneities induced by solid walls, making this type of system unsuitable for a comprehensive study of the effect on density inhomogeneity on nanofluidic flow. In this paper, we employ an external force compatible with periodic boundary conditions to induce the density variation, which greatly simplifies the problem when compared to flow in nonperiodic nanoconfined systems. Using the sinusoidal transverse force method to produce shearing velocity profiles and the sinusoidal longitudinal force method to produce inhomogeneous density profiles, we are able to observe the interactions between the two property inhomogeneities at the level of individual Fourier components. This gives us a method for direct measurement of the coupling between the density and velocity fields and allows us to introduce various feedback control mechanisms which customize fluid behavior in individual Fourier components. We briefly discuss the role of temperature inhomogeneity and consider whether local thermal expansion due to nonuniform viscous heating is sufficient to account for shear-induced density inhomogeneities. We also consider the local Newtonian constitutive relation relating the shear stress to the velocity gradient and show that the local model breaks down for sufficiently large density inhomogeneities over atomic length scales.

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Section: A Properties Of the Stf-slf Fluidmentioning

confidence: 99%

Section: A Properties Of the Stf-slf Fluidmentioning

confidence: 99%

Section: B Equations Of Motion For the Stf-slf Systemmentioning

confidence: 99%

Section: B Combined Stf-slf: Long Wavelength Density Perturbationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of nanoscale density inhomogeneities on shearing fluids

et al. 2013

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Nonequilibrium Molecular Dynamics

Todd

Daivis

2017

126

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Written by two specialists with over twenty-five years of experience in the field, this valuable text presents a wide range of topics within the growing field of nonequilibrium molecular dynamics (NEMD). It introduces theories which are fundamental to the field - namely, nonequilibrium statistical mechanics and nonequilibrium thermodynamics - and provides state-of-the-art algorithms and advice for designing reliable NEMD code, as well as examining applications for both atomic and molecular fluids. It discusses homogenous and inhomogenous flows and pays considerable attention to highly confined fluids, such as nanofluidics. In addition to statistical mechanics and thermodynamics, the book covers the themes of temperature and thermodynamic fluxes and their computation, the theory and algorithms for homogenous shear and elongational flows, response theory and its applications, heat and mass transport algorithms, applications in molecular rheology, highly confined fluids (nanofluidics), the phenomenon of slip and how to compute it from basic microscopic principles, and generalized hydrodynamics.

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How Local and Average Particle Diffusivities of Inhomogeneous Fluids Depend on Microscopic Dynamics

2014

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Computer simulations and a stochastic Fokker-Planck equation based approach are used to compare the single-particle diffusion coefficients of equilibrium hard-sphere fluids exhibiting identical inhomogeneous static structure and governed by either Brownian (i.e., overdamped Langevin) or Newtonian microscopic dynamics. The physics of inhomogeneity is explored via the imposition of one-dimensional sinusoidal density profiles of different wavelengths and amplitudes. When imposed density variations are small in magnitude for distances on the scale of a particle diameter, bulk-like average correlations between local structure and mobility are observed. In contrast, when density variations are significant on that length scale, qualitatively different structure-mobility correlations emerge that are sensitive to the governing microscopic dynamics. Correspondingly, a previously proposed scaling between long-time diffusivities for bulk isotropic fluids of particles exhibiting Brownian versus Newtonian dynamics [Pond et al. Soft Matter 2011, 7, 9859-9862] cannot be generalized to describe the position-dependent behaviors of strongly inhomogeneous fluids. While average diffusivities in the inhomogeneous and homogeneous directions are coupled, their qualitative dependencies on inhomogeneity wavelength are sensitive to the details of the microscopic dynamics. Nonetheless, average diffusivities of the inhomogeneous fluids can be approximately predicted for either type of dynamics based on knowledge of bulk isotropic fluid behavior and how inhomogeneity modifies the distribution of available volume. Analogous predictions for average diffusivities of experimental, inhomogeneous colloidal dispersions (based on known bulk behavior) suggest that they will exhibit qualitatively different trends than those predicted by models governed by overdamped Langevin dynamics that do not account for hydrodynamic interactions.

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Linear and nonlinear density response functions for a simple atomic fluid

Cited by 13 publications

References 24 publications

Effects of nanoscale density inhomogeneities on shearing fluids

Effects of nanoscale density inhomogeneities on shearing fluids

Nonequilibrium Molecular Dynamics

How Local and Average Particle Diffusivities of Inhomogeneous Fluids Depend on Microscopic Dynamics

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