--- trunk/COonPt/firstTry.tex	2013/03/19 18:08:24	3881
+++ trunk/COonPt/firstTry.tex	2013/03/20 17:50:18	3885
@@ -20,7 +20,9 @@
 \usepackage{graphicx}
 \usepackage{multirow}
 \usepackage{multicol}
-\usepackage{epstopdf}
+\usepackage{wrapfig}
+\mciteErrorOnUnknownfalse
+%\usepackage{epstopdf}
 
 \usepackage[version=3]{mhchem}  % this is a great package for formatting chemical reactions
 % \usepackage[square, comma, sort&compress]{natbib}
@@ -74,30 +76,18 @@ We examine surface reconstructions of Pt and Au(557) u
 
 
 \begin{abstract}
-We examine surface reconstructions of Pt and Au(557) under
-various CO coverages using molecular dynamics in order to 
-explore possible mechanisms for any observed reconstructions 
-and their dynamics. The metal-CO interactions were parameterized 
-as part of this work so that an efficient large-scale treatment of 
-this system could be undertaken. The large difference in binding 
-strengths of the metal-CO interactions was found to play a significant 
-role with regards to step-edge stability and adatom diffusion. A 
-small correlation between coverage and the diffusion constant 
-was also determined. The energetics of CO adsorbed to the surface 
-is sufficient to explain the reconstructions observed on the Pt 
-systems and the lack  of reconstruction of the Au systems.
-
-
-The mechanism and dynamics of surface reconstructions of Pt(557) 
-and Au(557) exposed to various coverages of carbon monoxide (CO) 
-were investigated using molecular dynamics simulations. Metal-CO 
-interactions were parameterized from experimental data and plane-wave 
-Density Functional Theory (DFT) calculations.  The large difference in 
-binding strengths of the Pt-CO and Au-CO interactions was found to play 
-a significant role in step-edge stability and adatom diffusion constants. 
-The energetics of CO adsorbed to the surface is sufficient to explain the 
-step-doubling reconstruction observed on Pt(557) and the lack of such 
-a reconstruction on the Au(557) surface.
+  The mechanism and dynamics of surface reconstructions of Pt(557) and
+  Au(557) exposed to various coverages of carbon monoxide (CO) were
+  investigated using molecular dynamics simulations. Metal-CO
+  interactions were parameterized from experimental data and
+  plane-wave Density Functional Theory (DFT) calculations.  The large
+  difference in binding strengths of the Pt-CO and Au-CO interactions
+  was found to play a significant role in step-edge stability and
+  adatom diffusion constants.  Various mechanisms for CO-mediated step
+  wandering and step doubling were investigated on the Pt(557)
+  surface.  We find that the energetics of CO adsorbed to the surface
+  can explain the step-doubling reconstruction observed on Pt(557) and
+  the lack of such a reconstruction on the Au(557) surface.
 \end{abstract}
 
 \newpage
@@ -219,11 +209,11 @@ properties,\cite{Chui:2003fk,Wang:2005qy,Medasani:2007
 The EAM, Finnis-Sinclair, and the Quantum Sutton-Chen (QSC) potentials
 have all been widely used by the materials simulation community for
 simulations of bulk and nanoparticle
-properties,\cite{Chui:2003fk,Wang:2005qy,Medasani:2007uq}
+properties,\cite{Chui:2003fk,Wang:2005qy,Medasani:2007uq,mishin99:_inter}
 melting,\cite{Belonoshko00,sankaranarayanan:155441,Sankaranarayanan:2005lr}
-fracture,\cite{Shastry:1996qg,Shastry:1998dx} crack
-propagation,\cite{BECQUART:1993rg} and alloying
-dynamics.\cite{Shibata:2002hh} One of EAM's strengths
+fracture,\cite{Shastry:1996qg,Shastry:1998dx,mishin01:cu} crack
+propagation,\cite{BECQUART:1993rg,Rifkin1992} and alloying
+dynamics.\cite{Shibata:2002hh,mishin02:b2nial,zope03:tial_ap,mishin05:phase_fe_ni} One of EAM's strengths
 is its sensitivity to small changes in structure. This arises
 because interactions
 up to the third nearest neighbor were taken into account in the parameterization.\cite{Voter95a}
@@ -234,11 +224,11 @@ theory (DFT) makes fitting DFT-derived cross potential
 surface structures. Additionally, the similarity of EAM's functional 
 treatment of the embedding energy to standard density functional 
 theory (DFT) makes fitting DFT-derived cross potentials with adsorbates somewhat easier.
-\cite{Foiles86,PhysRevB.37.3924,Rifkin1992,mishin99:_inter,mishin01:cu,mishin02:b2nial,zope03:tial_ap,mishin05:phase_fe_ni}  
 
 
 
 
+
 \subsection{Carbon Monoxide model}
 Previous explanations for the surface rearrangements center on
 the large linear quadrupole moment of carbon monoxide.\cite{Tao:2010}  
@@ -400,7 +390,7 @@ source molecular dynamics package, OpenMD.\cite{Ewald,
 data collection. All of the systems examined had at least 40~ns in the
 data collection stage, although simulation times for some Pt of the
 systems exceeded 200~ns.  Simulations were carried out using the open
-source molecular dynamics package, OpenMD.\cite{Ewald,OOPSE}
+source molecular dynamics package, OpenMD.\cite{Ewald,OOPSE,openmd}
 
 
 
@@ -472,7 +462,7 @@ the 50\% Pt system, experienced this reconstruction.
 
 %Evolution of surface
 \begin{figure}[H]
-\includegraphics[width=\linewidth]{EPS_ProgressionOfDoubleLayerFormation.pdf}
+\includegraphics[width=\linewidth]{EPS_ProgressionOfDoubleLayerFormation}
 \caption{The Pt(557) / 50\% CO system at a sequence of times after
   initial exposure to the CO: (a) 258~ps, (b) 19~ns, (c) 31.2~ns, and
   (d) 86.1~ns. Disruption of the (557) step-edges occurs quickly.  The
@@ -531,7 +521,7 @@ diffusion constants are shown in Figure \ref{fig:diff}
 
 %Diffusion graph
 \begin{figure}[H]
-\includegraphics[width=\linewidth]{Portrait_DiffusionComparison_1.pdf}
+\includegraphics[width=\linewidth]{Portrait_DiffusionComparison_1}
 \caption{Diffusion constants for mobile surface atoms along directions
   parallel ($\mathbf{D}_{\parallel}$) and perpendicular
   ($\mathbf{D}_{\perp}$) to the (557) step-edges as a function of CO
@@ -587,180 +577,200 @@ We have shown that a classical potential model is able
 
 %Discussion
 \section{Discussion}
-We have shown that a classical potential model is able to model the 
-initial reconstruction of the Pt(557) surface upon CO adsorption as 
-shown by Tao {\it et al}.\cite{Tao:2010}. More importantly, we were 
-able to observe features of the dynamic processes necessary for 
-this reconstruction. Here we discuss the features of the model that 
-give rise to the observed dynamical properties of the (557) reconstruction.
+We have shown that a classical potential is able to model the initial
+reconstruction of the Pt(557) surface upon CO adsorption, and have
+reproduced the double layer structure observed by Tao {\it et
+  al}.\cite{Tao:2010}. Additionally, this reconstruction appears to be
+rapid -- occurring within 100 ns of the initial exposure to CO.  Here
+we discuss the features of the classical potential that are
+contributing to the stability and speed of the Pt(557) reconstruction.
 
 \subsection{Diffusion}
-The perpendicular diffusion constant 
-appears to be the most important indicator of double layer 
-formation. As highlighted in Figure \ref{fig:reconstruct}, the 
-formation of the double layer did not begin until a nucleation 
-site appeared. And as mentioned by Williams {\it et al}.\cite{Williams:1991, Williams:1994}, 
-the inability for edges to cross leads to an effective edge-edge repulsion that 
-must be overcome to allow step coalescence. 
-A greater $\textbf{D}_\perp$ implies more step-wandering 
-and a larger chance for the stochastic meeting of two edges 
-to create a nucleation point. Parallel diffusion along the step-edge can help ``zipper'' up a nascent double 
-layer. This helps explain why the time scale for formation after 
-the appearance of a nucleation site was rapid, while the initial 
-appearance of the nucleation site was unpredictable. 
+The perpendicular diffusion constant appears to be the most important
+indicator of double layer formation. As highlighted in Figure
+\ref{fig:reconstruct}, the formation of the double layer did not begin
+until a nucleation site appeared.  Williams {\it et
+  al}.\cite{Williams:1991,Williams:1994} cite an effective edge-edge
+repulsion arising from the inability of edge crossing.  This repulsion
+must be overcome to allow step coalescence.  A larger
+$\textbf{D}_\perp$ value implies more step-wandering and a larger
+chance for the stochastic meeting of two edges to create a nucleation
+point.  Diffusion parallel to the step-edge can help ``zipper'' up a
+nascent double layer. This helps explain the rapid time scale for
+double layer completion after the appearance of a nucleation site, while
+the initial appearance of the nucleation site was unpredictable.
 
 \subsection{Mechanism for restructuring}
-Since the Au surface showed no large scale restructuring in any of 
-our simulations, our discussion will focus on the 50\% Pt-CO system 
-which did exhibit doubling. A 
-number of possible mechanisms exist to explain the role of adsorbed 
-CO in restructuring the Pt surface. Quadrupolar repulsion between 
-adjacent CO molecules adsorbed on the surface is one possibility.  
-However, the quadrupole-quadrupole interaction is short-ranged and 
-is attractive for some orientations.  If the CO molecules are ``locked'' in 
-a specific orientation relative to each other, through atop adsorption for 
-example, this explanation would gain credence. The calculated energetic repulsion 
-between two CO molecules located a distance of 2.77~\AA~apart 
-(nearest-neighbor distance of Pt) and both in a vertical orientation, 
-is 8.62 kcal/mol. Moving the CO to the second nearest-neighbor distance 
-of 4.8~\AA~drops the repulsion to nearly 0. Allowing the CO to rotate away 
-from a purely vertical orientation also lowers the repulsion. When the 
-carbons are locked at a distance of 2.77~\AA, a minimum of 6.2 kcal/mol is 
-reached when the angle between the 2 CO is $\sim$24\textsuperscript{o}. 
-The calculated barrier for surface diffusion of a Pt adatom is only 4 kcal/mol, so 
-repulsion between adjacent CO molecules bound to Pt could increase the surface 
-diffusion. However, the residence time of CO on Pt suggests that these 
-molecules are extremely mobile, with diffusion constants 40 to 2500 times 
-larger than surface Pt atoms. This mobility suggests that the CO molecules jump
-between different Pt atoms throughout the simulation, but will stay bound for 
-significant periods of time. 
+Since the Au surface showed no large scale restructuring in any of our
+simulations, our discussion will focus on the 50\% Pt-CO system which
+did exhibit doubling. A number of possible mechanisms exist to explain
+the role of adsorbed CO in restructuring the Pt surface. Quadrupolar
+repulsion between adjacent CO molecules adsorbed on the surface is one
+possibility.  However, the quadrupole-quadrupole interaction is
+short-ranged and is attractive for some orientations.  If the CO
+molecules are ``locked'' in a vertical orientation, through atop
+adsorption for example, this explanation would gain credence. The
+calculated energetic repulsion between two CO molecules located a
+distance of 2.77~\AA~apart (nearest-neighbor distance of Pt) and both
+in a vertical orientation, is 8.62 kcal/mol. Moving the CO to the
+second nearest-neighbor distance of 4.8~\AA~drops the repulsion to
+nearly 0. Allowing the CO to rotate away from a purely vertical
+orientation also lowers the repulsion. When the carbons are locked at
+a distance of 2.77~\AA, a minimum of 6.2 kcal/mol is reached when the
+angle between the 2 CO is $\sim$24\textsuperscript{o}.  The calculated
+barrier for surface diffusion of a Pt adatom is only 4 kcal/mol, so
+repulsion between adjacent CO molecules bound to Pt could increase the
+surface diffusion. However, the residence time of CO on Pt suggests
+that the CO molecules are extremely mobile, with diffusion constants 40
+to 2500 times larger than surface Pt atoms. This mobility suggests
+that the CO molecules jump between different Pt atoms throughout the
+simulation, but can stay bound for significant periods of time.
 
-A different interpretation of the above mechanism, taking into account the large 
-mobility of the CO, looks at how instantaneous and short-lived configurations of 
-CO on the surface can destabilize Pt-Pt interactions leading to increased step-edge 
-breakup and diffusion. On the bare Pt(557) surface the barrier to completely detach 
-an edge atom is $\sim$43~kcal/mol, as is shown in configuration (a) in Figures 
-\ref{fig:SketchGraphic} \& \ref{fig:SketchEnergies}. For certain configurations, cases 
-(e), (g), and (h), the barrier can be lowered to $\sim$23~kcal/mole. In these instances, 
-it becomes quite energetically favorable to roughen the edge by introducing a small 
-separation of 0.5 to 1.0~\AA. This roughening becomes immediately obvious in 
-simulations with significant CO populations. The roughening is present to a lesser extent 
-on lower coverage surfaces and even on the bare surfaces, although in these cases it is likely 
-due to stochastic vibrational processes that squeeze out step-edge atoms. The mechanism 
-of step-edge breakup suggested by these energy curves is one of the most difficult 
-processes, a complete break-away from the step-edge in one unbroken movement. 
-Easier multistep mechanisms likely exist where an adatom moves laterally on the surface 
-after being ejected so it ends up alongside the ledge. This provides the atom with 5 nearest 
-neighbors, which while lower than the 7 if it had stayed a part of the step-edge, is higher 
-than the 3 it could maintain located on the terrace. In this proposed mechanism, the CO 
-quadrupolar repulsion is still playing a primary role, but for its importance in roughening 
-the step-edge, rather than maintaining long-term bonds with a single Pt atom which is not 
-born out by their mobility data. The requirement for a large density of CO on the surface 
-for some of the more favorable suggested configurations in Figure \ref{fig:SketchGraphic} 
-correspond well with the increased mobility seen on higher coverage surfaces.
+A different interpretation of the above mechanism which takes the
+large mobility of the CO into account, would be in the destabilization
+of Pt-Pt interactions due to bound CO.  Destabilizing Pt-Pt bonds at
+the edges could lead to increased step-edge breakup and diffusion. On
+the bare Pt(557) surface the barrier to completely detach an edge atom
+is $\sim$43~kcal/mol, as is shown in configuration (a) in Figures
+\ref{fig:SketchGraphic} \& \ref{fig:SketchEnergies}. For certain
+configurations, cases (e), (g), and (h), the barrier can be lowered to
+$\sim$23~kcal/mol by the presence of bound CO molecules. In these
+instances, it becomes energetically favorable to roughen the edge by
+introducing a small separation of 0.5 to 1.0~\AA. This roughening
+becomes immediately obvious in simulations with significant CO
+populations. The roughening is present to a lesser extent on surfaces
+with lower CO coverage (and even on the bare surfaces), although in
+these cases it is likely due to random fluctuations that squeeze out
+step-edge atoms. Step-edge breakup by continuous single-atom
+translations (as suggested by these energy curves) is probably a
+worst-case scenario.  Multistep mechanisms in which an adatom moves
+laterally on the surface after being ejected would be more
+energetically favorable.  This would leave the adatom alongside the
+ledge, providing it with 5 nearest neighbors.  While fewer than the 7
+neighbors it had as part of the step-edge, it keeps more Pt neighbors
+than the 3 an isolated adatom would have on the terrace. In this
+proposed mechanism, the CO quadrupolar repulsion still plays a role in
+the initial roughening of the step-edge, but not in any long-term
+bonds with individual Pt atoms.  Higher CO coverages create more
+opportunities for the crowded CO configurations shown in Figure
+\ref{fig:SketchGraphic}, and this is likely to cause an increased
+propensity for step-edge breakup.
 
 %Sketch graphic of different configurations
 \begin{figure}[H]
-\includegraphics[width=0.8\linewidth, height=0.8\textheight]{COpathsSketch.pdf}
-\caption{The dark grey atoms refer to the upper ledge, while the white atoms are 
-the lower terrace. The blue highlighted atoms had a CO in a vertical atop position 
-upon them. These are a sampling of the configurations examined to gain a more 
-complete understanding of the effects CO has on surface diffusion and edge breakup. 
-Energies associated with each configuration are displayed in Figure \ref{fig:SketchEnergies}.}
+\includegraphics[width=\linewidth]{COpaths}
+\caption{Configurations used to investigate the mechanism of step-edge
+  breakup on Pt(557). In each case, the central (starred) atom is
+  pulled directly across the surface away from the step edge.  The Pt
+  atoms on the upper terrace are colored dark grey, while those on the
+  lower terrace are in white.  In each of these configurations, some
+  number of the atoms (highlighted in blue) had a CO molecule bound in
+  a vertical atop position.  The energies of these configurations as a
+  function of central atom displacement are displayed in Figure
+  \ref{fig:SketchEnergies}.}
 \label{fig:SketchGraphic}
 \end{figure}
 
 %energy graph corresponding to sketch graphic
 \begin{figure}[H]
-\includegraphics[width=\linewidth]{Portrait_SeparationComparison.pdf}
-\caption{The energy curves directly correspond to the labeled model 
-surface in Figure \ref{fig:SketchGraphic}. All energy curves are relative 
-to their initial configuration so the energy of a and h do not have the 
-same zero value. As is seen, certain arrangements of CO can lower 
-the energetic barrier that must be overcome to create an adatom. 
-However, it is the highest coverages where these higher-energy 
-configurations of CO will be more likely. }
+\includegraphics[width=\linewidth]{Portrait_SeparationComparison}
+\caption{Energies for displacing a single edge atom perpendicular to
+  the step edge as a function of atomic displacement. Each of the
+  energy curves corresponds to one of the labeled configurations in
+  Figure \ref{fig:SketchGraphic}, and are referenced to the
+  unperturbed step-edge.  Certain arrangements of bound CO (notably
+  configurations g and h) can lower the energetic barrier for creating
+  an adatom relative to the bare surface (configuration a).}
 \label{fig:SketchEnergies}
 \end{figure}
 
-While configurations of CO on the surface are able to increase diffusion, 
-this does not immediately provide an explanation for the formation of double 
-layers. If adatoms were constrained to their terrace then doubling would be 
-much less likely to occur. Nucleation sites could still potentially form, but there 
-would not be enough atoms to finish the doubling. For a non-simulated metal surface, where the 
-step lengths can be assumed to be infinite relative to atomic sizes, local doubling would be possible, but in 
-our simulations with our periodic treatment of the system, the system is not large enough to experience this effect. 
-Thus, there must be a mechanism that explains how adatoms are able to move 
-amongst terraces. Figure \ref{fig:lambda} shows points along a reaction coordinate 
-where an adatom along the step-edge with an adsorbed CO ``burrows'' into the 
-edge displacing an atom onto the higher terrace. This mechanism was chosen 
-because of similar events that were observed during the simulations. The barrier 
-heights we obtained are only approximations because we constrained the movement 
-of the highlighted atoms along a specific concerted path. The calculated $\Delta E$'s 
-are provide a strong energetic support for this modeled lifting mechanism. When CO is not present and 
-this reaction coordinate is followed, the $\Delta E > 3$~kcal/mol. The example shown 
-in the figure, where CO is present in the atop position, has a $\Delta E < -15$~kcal/mol. 
-While the barrier height is comparable for both cases, there is nearly a 20~kcal/mol 
-difference in energies and makes the process energetically favorable.
+While configurations of CO on the surface are able to increase
+diffusion and the likelihood of edge wandering, this does not provide
+a complete explanation for the formation of double layers. If adatoms
+were constrained to their original terraces then doubling could not
+occur.  A mechanism for vertical displacement of adatoms at the
+step-edge is required to explain the doubling.
 
+We have discovered one possible mechanism for a CO-mediated vertical
+displacement of Pt atoms at the step edge. Figure \ref{fig:lambda}
+shows four points along a reaction coordinate in which a CO-bound
+adatom along the step-edge ``burrows'' into the edge and displaces the
+original edge atom onto the higher terrace. A number of events similar
+to this mechanism were observed during the simulations.  We predict an
+energetic barrier of 20~kcal/mol for this process (in which the
+displaced edge atom follows a curvilinear path into an adjacent 3-fold
+hollow site).  The barrier heights we obtain for this reaction
+coordinate are approximate because the exact path is unknown, but the
+calculated energy barriers would be easily accessible at operating
+conditions.  Additionally, this mechanism is exothermic, with a final
+energy 15~kcal/mol below the original $\lambda = 0$ configuration.
+When CO is not present and this reaction coordinate is followed, the
+process is endothermic by 3~kcal/mol.  The difference in the relative 
+energies for the $\lambda=0$ and $\lambda=1$ case when CO is present
+provides strong support for CO-mediated Pt-Pt interactions giving rise
+to the doubling reconstruction. 
+
 %lambda progression of Pt -> shoving its way into the step
 \begin{figure}[H]
-\includegraphics[width=\linewidth]{EPS_rxnCoord.pdf}
-\caption{ Various points along a reaction coordinate are displayed in the figure. 
-The mechanism of edge traversal is examined in the presence of CO. The approximate
-barrier for the displayed process is 20~kcal/mol. However, the $\Delta E$ of this process
-is -15~kcal/mol making it an energetically favorable process.}
+\includegraphics[width=\linewidth]{EPS_rxnCoord}
+\caption{Points along a possible reaction coordinate for CO-mediated
+  edge doubling. Here, a CO-bound adatom burrows into an established
+  step edge and displaces an edge atom onto the upper terrace along a
+  curvilinear path.  The approximate barrier for the process is
+  20~kcal/mol, and the complete process is exothermic by 15~kcal/mol
+  in the presence of CO, but is endothermic by 3~kcal/mol without.}
 \label{fig:lambda}
 \end{figure}
 
-The mechanism for doubling on this surface appears to require the cooperation of at least 
-these two described processes. For complete doubling of a layer to occur there must 
-be the equivalent removal of a separate terrace. For those atoms to ``disappear'' from 
-that terrace they must either rise up on the ledge above them or drop to the ledge below 
-them. The presence of CO helps with the energetics of both of these situations. There must be sufficient 
-breakage of the step-edge to increase the concentration of adatoms on the surface and
-these adatoms must then undergo the burrowing highlighted above or some comparable 
-mechanism to traverse the step-edge. Over time, these mechanisms working in concert 
-lead to the formation of a double layer.
+The mechanism for doubling on the Pt(557) surface appears to require
+the cooperation of at least two distinct processes. For complete
+doubling of a layer to occur there must be a breakup of one
+terrace. These atoms must then ``disappear'' from that terrace, either
+by travelling to the terraces above of below their original levels.
+The presence of CO helps explain mechanisms for both of these
+situations. There must be sufficient breakage of the step-edge to
+increase the concentration of adatoms on the surface and these adatoms
+must then undergo the burrowing highlighted above (or a comparable
+mechanism) to create the double layer.  With sufficient time, these
+mechanisms working in concert lead to the formation of a double layer.
 
 \subsection{CO Removal and double layer stability}
-Once a double layer had formed on the 50\%~Pt system it 
-remained for the rest of the simulation time with minimal 
-movement. There were configurations that showed small 
-wells or peaks forming, but typically within a few nanoseconds 
-the feature would smooth away. Within our simulation time, 
-the formation of the double layer was irreversible and a double 
-layer was never observed to split back into two single layer 
-step-edges while CO was present. To further gauge the effect 
-CO had on this system, additional simulations were run starting 
-from a late configuration of the 50\%~Pt system that had formed 
-double layers. These simulations then had their CO removed. 
-The double layer breaks rapidly in these simulations, already 
-showing a well-defined splitting after 100~ps. Configurations of 
-this system are shown in Figure \ref{fig:breaking}. The coloring 
-of the top and bottom layers helps to exhibit how much mixing 
-the edges experience as they split. These systems were only 
-examined briefly, 10~ns, and within that time despite the initial 
-rapid splitting, the edges only moved another few \AA~apart.
-It is possible with longer simulation times that the 
-(557) lattice could be recovered as seen by Tao {\it et al}.\cite{Tao:2010}
+Once a double layer had formed on the 50\%~Pt system, it remained for
+the rest of the simulation time with minimal movement.  Random
+fluctuations that involved small clusters or divots were observed, but
+these features typically healed within a few nanoseconds.  Within our
+simulations, the formation of the double layer appeared to be
+irreversible and a double layer was never observed to split back into
+two single layer step-edges while CO was present. 
 
+To further gauge the effect CO has on this surface, additional
+simulations were run starting from a late configuration of the 50\%~Pt
+system that had already formed double layers. These simulations then
+had their CO forcibly removed.  The double layer broke apart rapidly
+in these simulations, showing a well-defined edge-splitting after
+100~ps. Configurations of this system are shown in Figure
+\ref{fig:breaking}. The coloring of the top and bottom layers helps to
+exhibit how much mixing the edges experience as they split. These
+systems were only examined for 10~ns, and within that time despite the
+initial rapid splitting, the edges only moved another few
+\AA~apart. It is possible that with longer simulation times, the (557)
+surface recovery observed by Tao {\it et al}.\cite{Tao:2010} could
+also be recovered.
 
-
 %breaking of the double layer upon removal of CO
 \begin{figure}[H]
-\includegraphics[width=\linewidth]{EPS_doubleLayerBreaking.pdf}
-\caption{(A)  0~ps, (B) 100~ps, (C) 1~ns, after the removal of CO. The presence of the CO
-helped maintain the stability of the double layer and its microfaceting of the double layer 
-into a (111) configuration. This microfacet immediately reverts to the original (100) step 
-edge which is a hallmark of the (557) surface. The separation is not a simple sliding apart, rather 
-there is a mixing of the lower and upper atoms at the edge.}
+\includegraphics[width=\linewidth]{EPS_doubleLayerBreaking}
+\caption{Dynamics of an established (111) double step after removal of
+  the adsorbed CO: (A) 0~ps, (B) 100~ps, and (C) 1~ns after the removal
+  of CO. The presence of the CO helped maintain the stability of the
+  double step.  Nearly immediately after the CO is removed, the step
+  edge reforms in a (100) configuration, which is also the step type
+  seen on clean (557) surfaces. The step separation involves
+  significant mixing of the lower and upper atoms at the edge.}
 \label{fig:breaking}
 \end{figure}
 
 
-
-
 %Peaks!
 %\begin{figure}[H]
 %\includegraphics[width=\linewidth]{doublePeaks_noCO.png}
@@ -774,7 +784,7 @@ there is a mixing of the lower and upper atoms at the 
 %Don't think I need this
 %clean surface...
 %\begin{figure}[H]
-%\includegraphics[width=\linewidth]{557_300K_cleanPDF.pdf}
+%\includegraphics[width=\linewidth]{557_300K_cleanPDF}
 %\caption{}
 
 %\end{figure}
@@ -782,18 +792,19 @@ The strength of the Pt-CO binding interaction as well 
 
 
 \section{Conclusion}
-The strength of the Pt-CO binding interaction as well as the large 
-quadrupolar repulsion between CO molecules are sufficient to 
-explain the observed increase in surface mobility and the resultant 
-reconstructions at the highest simulated coverage. The weaker 
-Au-CO interaction results in lower diffusion constants, less step-wandering, 
-and a lack of the double layer reconstruction. An in-depth examination 
-of the energetics shows the important role CO plays in increasing 
-step-breakup and in facilitating edge traversal which are both 
-necessary for double layer formation.
+The strength and directionality of the Pt-CO binding interaction, as
+well as the large quadrupolar repulsion between atop-bound CO
+molecules, help to explain the observed increase in surface mobility
+of Pt(557) and the resultant reconstruction into a double-layer
+configuration at the highest simulated CO-coverages.  The weaker Au-CO
+interaction results in significantly lower adataom diffusion
+constants, less step-wandering, and a lack of the double layer
+reconstruction on the Au(557) surface.
 
+An in-depth examination of the energetics shows the important role CO
+plays in increasing step-breakup and in facilitating edge traversal
+which are both necessary for double layer formation.
 
-
 %Things I am not ready to remove yet
 
 %Table of Diffusion Constants
@@ -817,17 +828,20 @@ Support for this project was provided by the National 
 % \end{table}
 
 \begin{acknowledgement}
-Support for this project was provided by the National Science
-Foundation under grant CHE-0848243 and by the Center for Sustainable
-Energy at Notre Dame (cSEND). Computational time was provided by the
-Center for Research Computing (CRC) at the University of Notre Dame.
+  We gratefully acknowledge conversations with Dr. William
+  F. Schneider and Dr. Feng Tao.  Support for this project was
+  provided by the National Science Foundation under grant CHE-0848243
+  and by the Center for Sustainable Energy at Notre Dame
+  (cSEND). Computational time was provided by the Center for Research
+  Computing (CRC) at the University of Notre Dame.
 \end{acknowledgement}
 \newpage
 \bibliography{firstTryBibliography}
 %\end{doublespace}
 
 \begin{tocentry}
-%\includegraphics[height=3.5cm]{timelapse}
+A reconstructed Pt(557) surface after having been exposed to a dosage of CO equivalent to half a monolayer of coverage is observed to undergo a doubling of the step-edge height and terrace length.
+\includegraphics[height=3.5cm]{TOC_doubleLayer}
 \end{tocentry}
 
 \end{document}
