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\begin{document} |
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\title{Simulating interfacial thermal conductance at metal-solvent |
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interfaces: the role of chemical capping agents} |
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\author{Shenyu Kuang and J. Daniel |
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Gezelter\footnote{Corresponding author. \ Electronic mail: gezelter@nd.edu} \\ |
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Department of Chemistry and Biochemistry,\\ |
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University of Notre Dame\\ |
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Notre Dame, Indiana 46556} |
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\date{\today} |
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\maketitle |
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\begin{doublespace} |
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\begin{abstract} |
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gezelter |
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The abstract version 2 |
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gezelter |
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\end{abstract} |
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\newpage |
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
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% BODY OF TEXT |
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% |
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\section{Introduction} |
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The intro. |
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skuang |
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\section{Methodology} |
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\subsection{Algorithm} |
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There have been many algorithms for computing thermal conductivity |
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using molecular dynamics simulations. However, interfacial conductance |
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is at least an order of magnitude smaller. This would make the |
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calculation even more difficult for those slowly-converging |
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equilibrium methods. Imposed-flux non-equilibrium |
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methods\cite{MullerPlathe:1997xw} have the flux set {\it a priori} and |
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the response of temperature or momentum gradients are easier to |
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measure than the flux, if unknown, and thus, is a preferable way to |
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the forward NEMD methods. Although the momentum swapping approach for |
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flux-imposing can be used for exchanging energy between particles of |
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different identity, the kinetic energy transfer efficiency is affected |
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by the mass difference between the particles, which limits its |
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application on heterogeneous interfacial systems. |
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The non-isotropic velocity scaling (NIVS)\cite{kuang:164101} approach in |
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non-equilibrium MD simulations is able to impose relatively large |
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kinetic energy flux without obvious perturbation to the velocity |
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distribution of the simulated systems. Furthermore, this approach has |
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the advantage in heterogeneous interfaces in that kinetic energy flux |
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can be applied between regions of particles of arbitary identity, and |
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the flux quantity is not restricted by particle mass difference. |
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The NIVS algorithm scales the velocity vectors in two separate regions |
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of a simulation system with respective diagonal scaling matricies. To |
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determine these scaling factors in the matricies, a set of equations |
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including linear momentum conservation and kinetic energy conservation |
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constraints and target momentum/energy flux satisfaction is |
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solved. With the scaling operation applied to the system in a set |
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frequency, corresponding momentum/temperature gradients can be built, |
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which can be used for computing transportation properties and other |
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applications related to momentum/temperature gradients. The NIVS |
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algorithm conserves momenta and energy and does not depend on an |
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external thermostat. |
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(wondering how much detail of algorithm should be put here...) |
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\subsection{Simulation Parameters} |
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Our simulation systems consists of metal gold lattice slab solvated by |
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organic solvents. In order to study the role of capping agents in |
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interfacial thermal conductance, butanethiol is chosen to cover gold |
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surfaces in comparison to no capping agent present. |
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The Au-Au interactions in metal lattice slab is described by the |
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quantum Sutton-Chen (QSC) formulation.\cite{PhysRevB.59.3527} The QSC |
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potentials include zero-point quantum corrections and are |
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reparametrized for accurate surface energies compared to the |
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Sutton-Chen potentials\cite{Chen90}. |
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Straight chain {\it n}-hexane and aromatic toluene are respectively |
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used as solvents. For hexane, both United-Atom\cite{TraPPE-UA.alkanes} |
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and All-Atom\cite{OPLSAA} force fields are used for comparison; for |
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toluene, United-Atom\cite{TraPPE-UA.alkylbenzenes} force fields are |
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used with rigid body constraints applied. (maybe needs more details |
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about rigid body) |
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Buatnethiol molecules are used as capping agent for some of our |
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simulations. United-Atom\cite{TraPPE-UA.thiols} and All-Atom models |
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are respectively used corresponding to the force field type of |
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solvent. |
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To describe the interactions between metal Au and non-metal capping |
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agent and solvent, we refer to Vlugt\cite{vlugt:cpc2007154} and derive |
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other interactions which are not parametrized in their work. (can add |
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hautman and klein's paper here and more discussion; need to put |
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aromatic-metal interaction approximation here) |
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\section{Computational Details} |
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Our simulation systems consists of a lattice Au slab with the (111) |
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surface perpendicular to the $z$-axis, and a solvent layer between the |
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periodic Au slabs along the $z$-axis. To set up the interfacial |
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system, the Au slab is first equilibrated without solvent under room |
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pressure and a desired temperature. After the metal slab is |
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equilibrated, United-Atom or All-Atom butanethiols are replicated on |
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the Au surface, each occupying the (??) among three Au atoms, and is |
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equilibrated under NVT ensemble. According to (CITATION), the maximal |
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thiol capacity on Au surface is $1/3$ of the total number of surface |
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Au atoms. |
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\cite{packmol} |
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gezelter |
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\section{Acknowledgments} |
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Support for this project was provided by the National Science |
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Foundation under grant CHE-0848243. Computational time was provided by |
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the Center for Research Computing (CRC) at the University of Notre |
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Dame. \newpage |
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\bibliography{interfacial} |
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\end{doublespace} |
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\end{document} |
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