| 74 |
|
conductivities and shear viscosities in a wide range of materials, |
| 75 |
|
from liquid copper to monatomic liquids to molecular fluids |
| 76 |
|
(e.g. ionic liquids).\cite{ISI:000246190100032} |
| 77 |
+ |
|
| 78 |
+ |
\begin{figure} |
| 79 |
+ |
\includegraphics[width=\linewidth]{thermalDemo} |
| 80 |
+ |
\caption{Demostration of thermal gradient estalished by RNEMD method.} |
| 81 |
+ |
\label{thermalDemo} |
| 82 |
+ |
\end{figure} |
| 83 |
|
|
| 84 |
|
RNEMD is preferable in many ways to the forward NEMD methods because |
| 85 |
|
it imposes what is typically difficult to measure (a flux or stress) |
| 582 |
|
\end{table*} |
| 583 |
|
|
| 584 |
|
\subsubsection{Crystal Gold} |
| 585 |
+ |
Our results of gold thermal conductivity used QSC force field are |
| 586 |
+ |
shown in Table \ref{AuThermal}. Although our calculation is smaller |
| 587 |
+ |
than experimental value by an order of more than 100, this difference |
| 588 |
+ |
is mainly attributed to the lack of electron interaction |
| 589 |
+ |
representation in our force field parameters. Richardson {\it et |
| 590 |
+ |
al.}\cite{ISI:A1992HX37800010} used similar force field parameters |
| 591 |
+ |
in their metal thermal conductivity calculations. The EMD method they |
| 592 |
+ |
employed in their simulations produced comparable results to |
| 593 |
+ |
ours. Therefore, it is confident to conclude that NIVS-RNEMD is |
| 594 |
+ |
applicable to metal force field system. |
| 595 |
|
|
| 596 |
|
\begin{figure} |
| 597 |
|
\includegraphics[width=\linewidth]{AuGrad} |
| 622 |
|
\end{minipage} |
| 623 |
|
\end{table*} |
| 624 |
|
|
| 609 |
– |
|
| 625 |
|
\subsection{Interfaciel Thermal Conductivity} |
| 626 |
< |
|
| 626 |
> |
After valid simulations of homogeneous water and gold systems using |
| 627 |
> |
NIVS-RNEMD method, calculation of gold/water interfacial thermal |
| 628 |
> |
conductivity was followed. It is found out that the interfacial |
| 629 |
> |
conductance is low due to a hydrophobic surface in our system. Figure |
| 630 |
> |
\ref{interfaceDensity} demonstrates this observance. Consequently, our |
| 631 |
> |
reported results (Table \ref{interfaceRes}) are of two orders of |
| 632 |
> |
magnitude smaller than our calculations on homogeneous systems. |
| 633 |
|
|
| 634 |
|
\begin{figure} |
| 635 |
|
\includegraphics[width=\linewidth]{interfaceDensity} |
| 638 |
|
\label{interfaceDensity} |
| 639 |
|
\end{figure} |
| 640 |
|
|
| 620 |
– |
|
| 641 |
|
\begin{figure} |
| 642 |
|
\includegraphics[width=\linewidth]{interfaceGrad} |
| 643 |
|
\caption{Temperature profiles for interfacial thermal conductivity |
| 645 |
|
\label{interfaceGrad} |
| 646 |
|
\end{figure} |
| 647 |
|
|
| 628 |
– |
|
| 629 |
– |
|
| 648 |
|
\begin{table*} |
| 649 |
|
\begin{minipage}{\linewidth} |
| 650 |
|
\begin{center} |
| 663 |
|
49.2 & 330.1 & 300.4 & 1.65(0.35) \\ |
| 664 |
|
\hline |
| 665 |
|
\end{tabular} |
| 666 |
< |
\label{AuThermal} |
| 666 |
> |
\label{interfaceRes} |
| 667 |
|
\end{center} |
| 668 |
|
\end{minipage} |
| 669 |
|
\end{table*} |
| 670 |
|
|
| 671 |
+ |
\section{Conclusions} |
| 672 |
+ |
NIVS-RNEMD simulation method is developed and tested on various |
| 673 |
+ |
systems. Simulation results demonstrate its validity of thermal |
| 674 |
+ |
conductivity calculations. NIVS-RNEMD improves non-Boltzmann-Maxwell |
| 675 |
+ |
distributions existing in previous RNEMD methods, and extends its |
| 676 |
+ |
applicability to interfacial systems. NIVS-RNEMD has also limited |
| 677 |
+ |
application on shear viscosity calculations, but under high momentum |
| 678 |
+ |
flux, it could cause temperature difference among different |
| 679 |
+ |
dimensions. Modification is necessary to extend the applicability of |
| 680 |
+ |
NIVS-RNEMD in shear viscosity calculations. |
| 681 |
|
|
| 682 |
|
\section{Acknowledgments} |
| 683 |
|
Support for this project was provided by the National Science |
