Rotational and translational diffusion of liquid n-hexane: EFP-based Molecular Dynamics analysis

Date
2022-02-28
Authors
Gordon, Mark
Evans, James
Garcia, Andres
Evans, James W.
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AIP Publishing LLC
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Chemistry
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Ames Laboratory
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Physics and Astronomy
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Mathematics
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ChemistryAmes LaboratoryPhysics and AstronomyMathematics
Abstract
Molecular Dynamics (MD) simulations based upon the Effective Fragment Potential (EFP) method are utilized to provide a comprehensive assessment of diffusion in liquid n-hexane. We decompose translational diffusion into components along and orthogonal to the long axis of the molecule. Rotational diffusion is decomposed into tumbling and spinning motions about this axis. Our analysis yields four corresponding diffusion coefficients which are related to diagonal entries in the complete 6 ´ 6 diffusion tensor accounting for the three rotational and three translational degrees of freedom, and for the potential coupling between them. However, coupling between different degrees of freedom is expected to be minimal for a natural choice of molecular body-fixed axis, so then off-diagonal entries in the tensor are negligible. This expectation is supported by a hydrodynamic analysis of the diffusion tensor which treats the liquid surrounding the molecule being tracked as a viscous continuum. Thus, the EFP MD analysis provides a comprehensive characterization of diffusion, and also reveals expected shortcomings of the hydrodynamic treatment particularly for rotational diffusion.
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The following article has been accepted by The Journal of Chemical Physics. After it is published, it will be found at DOI: 10.1063/5.0079212. Posted with permission.
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