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A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants
File | Description | Size | Format | |
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A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants.pdf | Accepted version | 1.59 MB | Adobe PDF | View/Open |
materials-09-00651-v2.pdf | Published version | 5.52 MB | Adobe PDF | View/Open |
Title: | A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants |
Authors: | Ewen, J Gattinoni, C Thakkar, F Morgan, N Spikes, H Dini, D |
Item Type: | Journal Article |
Abstract: | 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. |
Issue Date: | 2-Aug-2016 |
Date of Acceptance: | 28-Jul-2016 |
URI: | http://hdl.handle.net/10044/1/37594 |
DOI: | http://dx.doi.org/10.3390/ma9080651 |
ISSN: | 1996-1944 |
Publisher: | MDPI |
Journal / Book Title: | Materials |
Volume: | 9 |
Issue: | 8 |
Copyright Statement: | This is an open access article distributed under the Creative Commons Attribution License (CC BY 4.0). |
Sponsor/Funder: | Engineering & Physical Science Research Council (EPSRC) Shell Research Limited Engineering & Physical Science Research Council (EPSRC) |
Funder's Grant Number: | EP/G026114/1 PT36160 - PO 4550096336 EP/N025954/1 |
Keywords: | Chemical Sciences Engineering |
Publication Status: | Published |
Article Number: | 651 |
Appears in Collections: | Mechanical Engineering Faculty of Natural Sciences Faculty of Engineering |