--- trunk/COonPt/COonPtAu.tex	2013/06/05 21:22:46	3892
+++ trunk/COonPt/COonPtAu.tex	2013/06/12 19:30:39	3894
@@ -324,7 +324,7 @@ an effect on binding energies and binding site prefere
   \hline
   & Calculated & Experimental \\
   \hline
-  \multirow{2}{*}{\textbf{Pt-CO}} & \multirow{2}{*}{-1.84} & -1.4 \bibpunct{}{}{,}{n}{}{,}
+  \multirow{2}{*}{\textbf{Pt-CO}} & \multirow{2}{*}{-1.81} & -1.4 \bibpunct{}{}{,}{n}{}{,}
   (Ref. \protect\cite{Kelemen:1979}) \\
  & &  -1.9 \bibpunct{}{}{,}{n}{}{,} (Ref. \protect\cite{Yeo}) \\ \hline
   \textbf{Au-CO} & -0.39 & -0.40 \bibpunct{}{}{,}{n}{}{,}  (Ref. \protect\cite{TPDGold}) \\
@@ -335,44 +335,51 @@ The CO-metal cross interactions were compared directly
 
 
 \subsection{Forcefield validation}
-The CO-metal cross interactions were compared directly to DFT results
+The CO-Pt cross interactions were compared directly to DFT results
 found in the supporting information of Tao {\it et al.}
-\cite{Tao:2010} These calculations are estimates of the stabilization
-energy provided to double-layer reconstructions of the perfect 557
-surface by an overlayer of CO molecules in a $c (2 \times 4)$ pattern.
-To make the comparison, metal slabs that were five atoms thick and
-which displayed a 557 facet were constructed.  Double-layer
+\cite{Tao:2010}, while the CO-Au results are interpreted on their own.
+These calculations are estimates of the stabilization
+energy provided to double-layer reconstructions of the perfect (557)
+surface by an overlayer of CO molecules in a $c (2 \times 4)$ pattern.
+To make the comparison, metal slabs of both Pt and Au that were five atoms thick and
+which displayed a (557) facet were constructed.  Double-layer
 (reconstructed) systems were created using six atomic layers where
-enough of a layer was removed from both exposed 557 facets to create
+enough of a layer was removed from both exposed (557) facets to create
 the double step.  In all cases, the metal slabs contained 480 atoms
 and were minimized using steepest descent under the EAM force
 field. Both the bare metal slabs and slabs with 50\% carbon monoxide
 coverage (arranged in the $c (2 \times 4)$ pattern) were used.  The
 systems are periodic along and perpendicular to the step-edge axes
-with a large vacuum above the displayed 557 facet.
+with a large vacuum above the displayed (557) facet.
 
-Energies using our force field for the various systems are displayed
-in Table ~\ref{tab:steps}.  The relative energies are calculated as
-$E_{relative} = E_{system} - E_{M-557-S} - N_{CO} E_{CO-M}$,
-where $E_{CO-M}$ is -1.84 eV for CO-Pt and -0.39 eV for CO-Au. For
-platinum, the bare double layer is slightly less stable then the
-original single (557) step. However, addition of carbon monoxide
-stabilizes the reconstructed double layer relative to the perfect 557.
-This result is in qualitative agreement with DFT calculations in Tao
-{\it et al.}\cite{Tao:2010}, who also showed that the addition of CO
-leads to a reversal in stability.
-
-The DFT calculations suggest an increased stability of 0.08 kcal/mol
-(0.7128 eV) per Pt atom for going from the single to double step
-structure in the presence of carbon monoxide. 
+Energies calculated using our force field for the various systems are 
+displayed in Table ~\ref{tab:steps}.  The relative energies are calculated 
+as $E_{relative} = E_{system} - E_{M-557-S} - N_{CO}*E_{M-CO}$, 
+where $E_{M-CO}$ is -1.8 eV for CO-Pt and -0.39 eV for CO-Au. Our 
+calculated CO-Pt minimum is actually at -1.83 eV at a distance of 1.53~\AA, 
+which was obtained from single-atom liftoffs from a Pt(111) surface. The 
+arrangement of CO on the single and double steps however, leads to a 
+slight displacement from the minimum. For a 1 ps run at 3 K, the single 
+step Pt-CO average bond length was 1.60~\AA, and for the double step, 
+the bond length was 1.58~\AA. This slight increase is likely due to small 
+electrostatic interactions among the CO and the non-ideality of the surface. 
 
-The gold systems show much smaller energy differences between the
-single and double layers. The weaker binding of CO to Au is evidenced
-by the much smaller change in relative energy between the structures
-when carbon monoxide is present.  Additionally, as CO-Au binding is
-much weaker than CO-Pt, it would be unlikely that CO would approach
-the 50\% coverage levels operating temperatures for the gold surfaces.
+For platinum, the bare double layer is less stable then the original single 
+(557) step by about 0.25 kcal/mole per Pt atom. However, addition of carbon 
+monoxide to the double step system provides a greater amount of stabilization 
+when compared to single step system with CO on the order of 230 kcal/mole 
+for this system size. The absolute difference is minimal, but this result is in 
+qualitative agreement with DFT calculations in Tao {\it et al.}\cite{Tao:2010}, 
+who also showed that the addition of CO leads to a reversal in stability.
 
+The gold systems show a smaller energy difference between the clean 
+single and double layers when compared to platinum. Upon addition of 
+CO however, the single step surface becomes much more stable. These 
+results, while helpful, need to be tempered by the weaker binding energy 
+of CO to Au. From our simulations we see that at the elevated temperatures 
+we are running at, it is difficult for the gold systems to maintain > than 25\% 
+coverage, despite their being enough CO in the system. 
+
 %Table of single step double step calculations
 \begin{table}[H]
   \caption{Minimized single point energies of (S)ingle and (D)ouble
@@ -386,15 +393,15 @@ Pt(557)-D & 480 & 0 & 114.783 & 0.239 & -\\
 \textbf{Step} & \textbf{N}\textsubscript{M} & \textbf{N\textsubscript{CO}} & \textbf{Relative Energy} & \textbf{$\Delta$E/M} & \textbf{$\Delta$E/CO} \\
 \hline
 Pt(557)-S & 480 & 0 & 0 & 0 & - \\
-Pt(557)-D & 480 & 0 & 114.783 & 0.239 & -\\
-Pt(557)-S & 480 & 40 & -124.546 & -0.259 & -3.114\\
-Pt(557)-D & 480 & 44 & -34.953 & -0.073 & -0.794\\
+Pt(557)-D & 480 & 0 & 119.788 & 0.2495 & -\\
+Pt(557)-S & 480 & 40 & -109.734 & -0.2286 & -2.743\\
+Pt(557)-D & 480 & 48 & -110.039 & -0.2292 & -2.292\\
 \hline
 \hline
 Au(557)-S & 480 & 0 & 0 & 0 & - \\
-Au(557)-D & 480 & 0 & 79.572 & 0.166 & - \\
-Au(557)-S & 480 & 40 & -157.199 & -0.327 & -3.930\\
-Au(557)-D & 480 & 44 & -123.297 & -0.257 & -2.802 \\
+Au(557)-D & 480 & 0 & 83.853 & 0.1747 & - \\
+Au(557)-S & 480 & 40 & -253.604 & -0.5283 & -6.340\\
+Au(557)-D & 480 & 48 & -156.150 & -0.3253 & -3.253 \\
 \hline
 \end{tabular}
 \label{tab:steps}
