--- trunk/COonPt/COonPtAu.tex	2013/06/04 20:22:12	3890
+++ trunk/COonPt/COonPtAu.tex	2013/06/05 18:27:19	3891
@@ -332,45 +332,54 @@ an effect on binding energies and binding site prefere
 \end{tabular}
 \label{tab:co_energies}
 \end{table}
-
 
-\subsection{Validation of forcefield selections}
-By calculating minimum energies for commensurate systems of 
-single and double layer Pt and Au systems with 0 and 50\% coverages 
-(arranged in a c(2x4) pattern), our forcefield selections were able to be 
-indirectly compared to results shown in the supporting information of Tao 
-{\it et al.} \cite{Tao:2010}. Five layer thick systems, displaying a 557 facet 
-were constructed, each composed of 480 metal atoms. Double layers systems 
-were constructed from six layer thick systems where an entire layer was 
-removed from both displayed facets to create a double step. By design, the 
-double step system also contains 480 atoms, five layers thick, so energy 
-comparisons between the arrangements can be made directly. The positions
-of the atoms were allowed to relax, along with the box sizes, before a
-minimum energy was calculated. Carbon monoxide, equivalent to 50\%
-coverage on one side of the metal system was added in a c(2x4) arrangement
-and again allowed to relax before a minimum energy was calculated.
 
-Energies for the various systems are displayed in Table ~\ref{tab:steps}. Examining
-the Pt systems first, it is apparent that the double layer system is slightly less stable
-then the original single step. However, upon addition of carbon monoxide, the 
-stability is reversed and the double layer system becomes more stable. This result
-is in agreement with DFT calculations in Tao {\it et al.}\cite{Tao:2010}, who also show
-that the addition of CO leads to a reversal in the most stable system. While our
-results agree qualitatively, quantitatively, they are approximately an order of magnitude
-different. Looking at additional stability per atom in kcal/mol, the DFT calculations suggest
-an increased stability of 0.1 kcal/mol per Pt atom, whereas we are seeing closer to a 0.4 kcal/mol
-increase in stability per Pt atom.
-
-The gold systems show a much smaller energy difference between the single and double
-systems, likely arising from their lower energy per atom values. Additionally, the weaker
-binding of CO to Au is evidenced by the much smaller energy change between the two systems,
-when compared to the Pt results. This limited change helps explain our lack of any reconstruction
-on the Au systems.
+\subsection{Forcefield validation}
+The CO-metal 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
+(reconstructed) systems were created using six atomic layers where
+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.
 
+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 0.1 kcal/mol
+per Pt atom, while our force field gives an approximately 0.4 kcal/mol
+increase in stability per Pt atom.  
+
+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, it would be unlikely that CO would approach the 50\%
+coverage levels operating temperatures.
 
 %Table of single step double step calculations
 \begin{table}[H]
-\caption{Minimized single point energies of unit cell crystals displaying (S)ingle or (D)double steps. Systems are periodic along and perpendicular to the step-edge axes with a large vacuum above the displayed 557 facet. The relative energies are calculated as $E_{relative} = E_{system} - E_{M-557-S} - N_{CO}\Delta E_{CO-M}$ , where $E_{CO-M}$  is -1.84 eV for Pt-CO and -0.39 eV for Pt-CO. The addition of CO in a 50\% c(2x4) coverage acts as a stabilizing presence and suggests a driving force for the observed reconstruction on the highest coverage Pt system. All energies are in kcal/mol.}
+  \caption{Minimized single point energies of (S)ingle and (D)ouble
+    steps.  The addition of CO in a 50\% $c(2 \times 4)$ coverage acts as a
+    stabilizing presence and suggests a driving force for the observed
+    reconstruction on the highest coverage Pt system. All energies are
+    in kcal/mol.} 
 \centering
 \begin{tabular}{| c | c | c | c | c | c |}
 \hline
