Shear viscosity of linear alkanes through molecular simulations: quantitative tests for<i>n</i>-decane and<i>n</i>-hexadecane

Payal, Rajdeep Singh; Balasubramanian, Sundaram; Rudra, Indranil; Tandon, Kunj; Mahlke, Ingo; Doyle, David; Cracknell, Roger

doi:10.1080/08927022.2012.702423

Cited by 33 publications

(39 citation statements)

References 36 publications

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“…Figure 2 in Ref. [29] demonstrates that an average of 10 short replicate simulations converges to the same value as a single long simulation. Since these replicates can be performed in parallel, the real time is reduced, although the CPU time may be the same or more.…”

Section: Replicate Simulationsmentioning

confidence: 92%

“…For example, the fluctuations in η are much smaller for the average of 10 replicates compared to that of a single longer simulation (see Figure 2 of Ref. [29]). As fluctuations in η are typically much larger than D, more replicate simulations are required for estimating viscosity (see Sec.…”

Section: Replicate Simulationsmentioning

confidence: 99%

“…The number of replicates used in the literature varies widely. In their study of the shear viscosity of alkanes, Payal and co-workers [29] used 10 replicates, whereas Zhang et al [30] performed a systematic investigation of the minimal number of replicates required for convergence. They observed that a value of 30 to 40 replicates was statistically equivalent to 100 replicates for their system.…”

Section: Improved Precisionmentioning

confidence: 99%

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Best Practices for Computing Transport Properties 1. Self-Diffusivity and Viscosity from Equilibrium Molecular Dynamics [Article v1.0]

et al. 2020

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The ability to predict transport properties (e.g., diffusivity, viscosity, and conductivity) is one of the primary benefits of molecular simulation. Although most studies focus on the accuracy of the simulation output compared to experimental data, such a comparison primarily tests the adequacy of the force field (i.e., the model). By contrast, the reliability of different simulation methodologies for predicting transport properties is the focus of this manuscript. Unfortunately, obtaining reproducible estimates of transport properties from molecular simulation is not as straightforward as static properties. Therefore, this manuscript discusses the best practices that should be followed to ensure that the simulation output is reliable, i.e., is a valid representation of the force field implemented. We also discuss procedures to use so that the results are reproducible (i.e., can be obtained by other researchers following the same methods and procedures). There are two classes by which transport properties are predicted: equilibrium molecular dynamics (EMD) and non-equilibrium molecular dynamics (NEMD). This manuscript presents the best practices for EMD, leaving NEMD for a future publication. As self-diffusivity and shear viscosity are the most prevalent transport properties found in the literature, the discussion will also be limited to these properties with the expectation that future publications will discuss best practices for thermal conductivity, ionic conductivity, and multicomponent diffusivity.

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Section: Replicate Simulationsmentioning

confidence: 92%

Section: Replicate Simulationsmentioning

confidence: 99%

Section: Improved Precisionmentioning

confidence: 99%

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Best Practices for Computing Transport Properties 1. Self-Diffusivity and Viscosity from Equilibrium Molecular Dynamics [Article v1.0]

et al. 2020

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“…In an MD force-field, the liquid density is mainly governed by the non-bonded (Lennard-Jones and Coulombic) interactions, whilst the viscosity is also heavily influenced by the ‘stiffness’ of the torsional potential [ 12 , 13 ]. Previous studies have compared all-atom and united-atom force-field performance in terms of their density and viscosity prediction of long-chain alkanes [ 13 , 14 , 15 ]; however, they have been limited to only a few variants, and have not included recent parameterizations specifically designed for long-chain molecules [ 16 , 17 ]. These previous comparisons have shown that united-atom force-fields consistently under-predict the viscosity of long-chain linear alkanes, with the prediction accuracy deteriorating when longer chain molecules or high pressures are used [ 13 , 14 , 15 ].…”

Section: Introductionmentioning

confidence: 99%

A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants

et al. 2016

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For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD) simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, the accuracy of the results depend on the chosen force-field. In this study, we demonstrate that the use of an accurate, all-atom force-field is critical in order to; (i) accurately predict important properties of long-chain, linear molecules; and (ii) reproduce experimental friction behavior of multi-component tribological systems. In particular, we focus on n-hexadecane, an important model lubricant with a wide range of industrial applications. Moreover, simulating conditions common in tribological systems, i.e., high temperatures and pressures (HTHP), allows the limits of the selected force-fields to be tested. In the first section, a large number of united-atom and all-atom force-fields are benchmarked in terms of their density and viscosity prediction accuracy of n-hexadecane using equilibrium molecular dynamics (EMD) simulations at ambient and HTHP conditions. Whilst united-atom force-fields accurately reproduce experimental density, the viscosity is significantly under-predicted compared to all-atom force-fields and experiments. Moreover, some all-atom force-fields yield elevated melting points, leading to significant overestimation of both the density and viscosity. In the second section, the most accurate united-atom and all-atom force-field are compared in confined NEMD simulations which probe the structure and friction of stearic acid adsorbed on iron oxide and separated by a thin layer of n-hexadecane. The united-atom force-field provides an accurate representation of the structure of the confined stearic acid film; however, friction coefficients are consistently under-predicted and the friction-coverage and friction-velocity behavior deviates from that observed using all-atom force-fields and experimentally. This has important implications regarding force-field selection for NEMD simulations of systems containing long-chain, linear molecules; specifically, it is recommended that accurate all-atom potentials, such as L-OPLS-AA, are employed.

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“…Quantitative comparisons between several popular force-fields for NEMD simulations of lubricants can be found elsewhere [10,76,77], but a brief overview is also provided here for completeness. Most historic simulations of tribological systems which include alkane molecules have employed united-atom (UA) force-fields where the nonpolar hydrogens are grouped with the carbon atoms to generate CH, CH 2 and CH 3 pseudo-atoms [10].…”

Section: Classical Force-fieldsmentioning

confidence: 99%

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

2018

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Nonequilibrium molecular dynamics (NEMD) simulations have provided unique insights into the nanoscale behaviour of lubricants under shear. This review discusses the early history of NEMD and its progression from a tool to corroborate theories of the liquid state, to an instrument that can directly evaluate important fluid properties, towards a potential design tool in tribology. The key methodological advances which have allowed this evolution are also highlighted. This is followed by a summary of bulk and confined NEMD simulations of liquid lubricants and lubricant additives, as they have progressed from simple atomic fluids to ever more complex, realistic molecules. The future outlook of NEMD in tribology, including the inclusion of chemical reactivity for additives, and coupling to continuum methods for large systems, is also briefly discussed.

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Shear viscosity of linear alkanes through molecular simulations: quantitative tests forn-decane andn-hexadecane

Cited by 33 publications

References 36 publications

Best Practices for Computing Transport Properties 1. Self-Diffusivity and Viscosity from Equilibrium Molecular Dynamics [Article v1.0]

Best Practices for Computing Transport Properties 1. Self-Diffusivity and Viscosity from Equilibrium Molecular Dynamics [Article v1.0]

A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

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