| 213 |
|
\hline |
| 214 |
|
\multicolumn{5}{|c|}{\textbf{Self-Interactions}}\\ |
| 215 |
|
\hline |
| 216 |
< |
& r & $\sigma$ & $\epsilon$ & q\\ |
| 216 |
> |
& {\it z} & $\sigma$ & $\epsilon$ & q\\ |
| 217 |
|
\hline |
| 218 |
< |
\textbf{C} & 0.0 & 0.0262 & 3.83 & -0.75 \\ |
| 219 |
< |
\textbf{O} & 1.13 & 0.1591 & 3.12 & -0.85 \\ |
| 220 |
< |
\textbf{M} & 0.6457 & - & - & 1.6 \\ |
| 218 |
> |
\textbf{C} & -0.6457 & 0.0262 & 3.83 & -0.75 \\ |
| 219 |
> |
\textbf{O} & 0.4843 & 0.1591 & 3.12 & -0.85 \\ |
| 220 |
> |
\textbf{M} & 0.0 & - & - & 1.6 \\ |
| 221 |
|
\hline |
| 222 |
|
\end{tabular} |
| 223 |
|
\end{table} |
| 270 |
|
|
| 271 |
|
\subsection{Construction and Equilibration of 557 Metal interfaces} |
| 272 |
|
|
| 273 |
< |
Our model systems are composed of approximately 4000 metal atoms cut along the 557 plane so that they are periodic in the \it{x} and \it{y} directions exposing the 557 plane in the \it{z} direction. Runs at various temperatures ranging from 300~K to 1200~K were started with the intent of viewing relative stability of the surface when CO was not present in the system. Owing to the different melting points (1337~K for Au and 2045~K for Pt), the bare crystal systems were initially run in the Canonical ensemble for at 800~K and 1000~K respectively for 100 ps. Various amounts of CO were placed in the vacuum portion which upon full adsorption to the surface corresponded to 5\%, 25\%, 33\%, and 50\% coverages. These systems were again allowed to reach thermal equilibrium before being run in the micro canonical ensemble. All of the systems examined were run for at least 40 ns. A subset that were undergoing interesting effects have been allowed to continue running with one system approaching 200 ns.em |
| 273 |
> |
Our model systems are composed of approximately 4000 metal atoms |
| 274 |
> |
cut along the 557 plane so that they are periodic in the {\it x} and {\it y} |
| 275 |
> |
directions exposing the 557 plane in the {\it z} direction. Runs at various |
| 276 |
> |
temperatures ranging from 300~K to 1200~K were started with the intent |
| 277 |
> |
of viewing relative stability of the surface when CO was not present in the |
| 278 |
> |
system. Owing to the different melting points (1337~K for Au and 2045~K for Pt), |
| 279 |
> |
the bare crystal systems were initially run in the Canonical ensemble at |
| 280 |
> |
800~K and 1000~K respectively for 100 ps. Various amounts of CO were |
| 281 |
> |
placed in the vacuum region, which upon full adsorption to the surface |
| 282 |
> |
corresponded to 5\%, 25\%, 33\%, and 50\% coverages. These systems |
| 283 |
> |
were again allowed to reach thermal equilibrium before being run in the |
| 284 |
> |
microcanonical ensemble. All of the systems examined in this work were |
| 285 |
> |
run for at least 40 ns. A subset that were undergoing interesting effects |
| 286 |
> |
have been allowed to continue running with one system approaching 200 ns. |
| 287 |
> |
All simulations were run using the open source molecular dynamics package, OpenMD. \cite{Ewald, OOPSE} |
| 288 |
|
|
| 289 |
|
|
| 290 |
|
|
| 341 |
|
%Table of Diffusion Constants |
| 342 |
|
%Add gold?M |
| 343 |
|
\begin{table}[H] |
| 344 |
< |
\caption{Platinum diffusion constants parallel and perpendicular to the 557 step edge. As the coverage increases, the diffusion constants parallel and perpendicular to the step edge both initially increase and then decrease slightly. There were two approaches of analysis. One looking at the surface atoms that had moved more than a prescribed amount over the run time and the other looking at all surface atoms. Units are \AA\textsuperscript{2}/ns} |
| 344 |
> |
\caption{Platinum and gold diffusion constants parallel and perpendicular to the 557 step edge. As the coverage increases, the diffusion constants parallel and perpendicular to the step edge both initially increase and then decrease slightly. Units are \AA\textsuperscript{2}/ns} |
| 345 |
|
\centering |
| 346 |
< |
\begin{tabular}{| c | ccc | ccc | c |} |
| 346 |
> |
\begin{tabular}{| c | cc | cc | c |} |
| 347 |
|
\hline |
| 348 |
< |
\textbf{System Coverage} & $\mathbf{D}_{\parallel}$ & $\mathbf{D}_{\perp}$ & \textbf{Atoms} & $\mathbf{D}_{\parallel}$ & $\mathbf{D}_{\perp}$ & \textbf{Atoms} & \textbf{Time (ns)}\\ |
| 348 |
> |
\textbf{System Coverage} & $\mathbf{D}_{\parallel}$ & $\mathbf{D}_{\perp}$ & $\mathbf{D}_{\parallel}$ & $\mathbf{D}_{\perp}$ & \textbf{Time (ns)}\\ |
| 349 |
|
\hline |
| 350 |
< |
&\multicolumn{3}{c|}{\textbf{Mobile}}&\multicolumn{3}{c|}{\textbf{Surface Atoms}} & \\ |
| 350 |
> |
&\multicolumn{2}{c|}{\textbf{Platinum}}&\multicolumn{2}{c|}{\textbf{Gold}} & \\ |
| 351 |
|
\hline |
| 352 |
< |
50\% & 3.74 & 0.89 & 497 & 2.05 & 0.49 & 912 & 116 \\ |
| 353 |
< |
50\% & 5.81 & 1.59 & 365 & 2.41 & 0.68 & 912 & 46 \\ |
| 354 |
< |
33\% & 6.73 & 2.47 & 332 & 2.51 & 0.93 & 912 & 46 \\ |
| 355 |
< |
25\% & 5.38 & 2.04 & 361 & 2.18 & 0.84 & 912 & 46 \\ |
| 356 |
< |
5\% & 5.54 & 0.63 & 230 & 1.44 & 0.19 & 912 & 46 \\ |
| 343 |
< |
0\% & 3.53 & 0.61 & 282 & 1.11 & 0.22 & 912 & 56 \\ |
| 344 |
< |
\hline |
| 345 |
< |
50\%-r & 6.91 & 2.00 & 198 & 2.23 & 0.68 & 925 & 25\\ |
| 346 |
< |
0\%-r & 4.73 & 0.27 & 128 & 0.72 & 0.05 & 925 & 43\\ |
| 352 |
> |
50\% & 4.32 $\pm$ 0.02 & 1.185 $\pm$ 0.008 & 1.72 $\pm$ 0.02 & 0.455 $\pm$ 0.006 & 40 \\ |
| 353 |
> |
33\% & 5.18 $\pm$ 0.03 & 1.999 $\pm$ 0.005 & 1.95 $\pm$ 0.02 & 0.337 $\pm$ 0.004 & 40 \\ |
| 354 |
> |
25\% & 5.01 $\pm$ 0.02 & 1.574 $\pm$ 0.004 & 1.26 $\pm$ 0.03 & 0.377 $\pm$ 0.006 & 40 \\ |
| 355 |
> |
5\% & 3.61 $\pm$ 0.02 & 0.355 $\pm$ 0.002 & 1.84 $\pm$ 0.03 & 0.169 $\pm$ 0.004 & 40 \\ |
| 356 |
> |
0\% & 3.27 $\pm$ 0.02 & 0.147 $\pm$ 0.004 & 1.50 $\pm$ 0.02 & 0.194 $\pm$ 0.002 & 40 \\ |
| 357 |
|
\hline |
| 358 |
|
\end{tabular} |
| 359 |
|
\end{table} |
