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Decomposition of the molecular orientational time correlation function showed |
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different behavior for the short- and longer-time decay components approaching |
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normal to the interface. Lastly we show through calculation of the interfacial |
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friction coefficient that the basal and pyramidal facets are more |
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friction coefficient and dynamic water contact angle measurement |
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that the basal and pyramidal facets are more |
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hydrophilic than the prismatic and secondary prismatic facets.} |
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\end{abstract} |
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|
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\keywords{ice|water|interface|contact angle|molecular dynamics} |
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|
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\abbreviations{QLL, quasi liquid layer; MD, molecular dynamics} |
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%\abbreviations{QLL, quasi liquid layer; MD, molecular dynamics} |
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|
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%\dropcap{I}n this article we study the evolution of ``almost-sharp'' fronts |
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%for the surface quasi-geostrophic equation. This 2-D active scalar |
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apparent independence of water model on interfacial width, we have chosen to use the rigid SPC/E |
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water model in this study. |
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|
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\subsection{Pyramidal and secondary prismatic system construction} |
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\subsection{Pyramidal and secondary prismatic ice/water interface construction} |
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To construct the pyramidal and secondary prismatic ice/water systems, |
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first a proton-ordered zero dipole crystal of ice-I$_\mathrm{h}$ with exposed strips |
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of H-atoms and lone pairs was constructed from Structure 6 of Hirsch |
194 |
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three times that of the ice block. Each of the ice slabs and water |
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boxes were independently equilibrated to 50K, and the resulting |
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systems were merged by carving out any liquid water molecules within 3 |
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\AA\ of any atoms in the ice slabs. For a more detailed explanation of |
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> |
\AA\ of any atoms in the ice slabs. Each of the combined ice/water |
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> |
systems were then equilibrated to 225K, which was found to be a stable |
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temperature for each of the interfaces over a 5 ns simulation. |
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> |
For a more detailed explanation of |
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|
the ice/water systems construction, please refer to a previous |
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|
paper\cite{Louden13}. The resulting dimensions, number of ice, and liquid water molecules |
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contained in each of these systems can be seen in Table \ref{tab:method}. |
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% Do we need to justify the sims at 225K? |
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% No crystal growth or shrinkage over 2 successive 1 ns NVT simulations for |
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% either the pyramidal or sec. prismatic ice/water systems. |
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+ |
To perform the shearing simulations, the velocity shearing and scaling |
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+ |
varient of reverse nonequilibrium molecular dynamics (VSS-RNEMD) was |
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conducted. This method performs a series of simultaneous velocity |
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+ |
exchanges between two regions of the simulation cell, to |
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+ |
simultaneously create a velocity and temperature gradient. The thermal |
213 |
+ |
gradient is necessary when performing shearing simulations as to |
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+ |
prevent frictional heating from the shear from melting the |
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+ |
interface. For more details on the VSS-RNEMD method please refer to a |
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+ |
pervious paper\cite{Louden13}. |
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|
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|
The computational details performed here were equivalent to those reported |
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in our previous publication\cite{Louden13}. The only changes made to the |
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previously reported procedure were the following. VSS-RNEMD moves were |
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attempted every 2 fs instead of every 50 fs. This was done to minimize |
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> |
in a previous publication\cite{Louden13}, with the following changes. |
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> |
VSS-RNEMD moves were attempted every 2 fs instead of every 50 fs. This was done to minimize |
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|
the magnitude of each individual VSS-RNEMD perturbation to the system. |
210 |
– |
|
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|
All pyramidal simulations were performed under the canonical (NVT) ensamble |
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except those |
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< |
during which statistics were accumulated for the orientational correlation |
223 |
> |
except those during which configurations were accumulated for the orientational correlation |
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|
function, which were performed under the microcanonical (NVE) ensamble. All |
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< |
secondary prismatic |
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simulations were performed under the NVE ensamble. |
225 |
> |
secondary prismatic simulations were performed under the NVE ensamble. |
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|
|
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|
\subsection{Droplet simulations} |
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Here, we will calculate the contact angle of a water droplet as it spreads |
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across each of the four ice I$_\mathrm{h}$ crystal facets in order to |
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determine the surface's relative hydrophilicites. The ice surfaces were |
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oriented so that the desired facet was exposed to the positive z dimension. |
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The sizes and number of molecules in each of the surfaces is given in Table |
228 |
> |
To construct ice surfaces to perform water contact angle calculations |
229 |
> |
on, ice crystals were created as described earlier (see Pyramidal and |
230 |
> |
secondary prismatic ice/water interface construction). The crystals |
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> |
were then cut from the negative $z$ dimension, ensuring the remaining |
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> |
ice crystal was thicker in $z$ than the potential cutoff. The crystals |
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> |
were then replicated in $x$ and $y$ until a sufficiently large surface |
234 |
> |
had been created. The sizes and number of molecules in each of the surfaces is given in Table |
235 |
|
\ref{tab:ice_sheets}. Molecular restraints were applied to the center of mass |
236 |
|
of the rigid bodies to prevent surface melting, however the molecules were |
237 |
< |
allowed to reorient themselves freely. The water doplet to be placed on the |
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< |
surface contained 2048 SPC/E molecules, which has been found to produce |
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> |
allowed to reorient themselves freely. The water doplet contained 2048 |
238 |
> |
SPC/E molecules, which has been found to produce |
239 |
|
agreement for the Young contact angle extrapolated to an infinite drop |
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< |
size\cite{Daub10}. The surfaces and droplet were equilibrated to 225 K, at |
241 |
< |
which time the droplet was placed 3-5 \AA\ above the surface at 5 unique |
242 |
< |
locations. Each simulation was 5 ns in length and conducted in the NVE |
243 |
< |
ensemble. |
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> |
size\cite{Daub10}. The surfaces and droplet were independently |
241 |
> |
equilibrated to 225 K, at which time the droplet was placed 3-5 \AA\ |
242 |
> |
above the positive $z$ dimension of the surface at 5 unique |
243 |
> |
locations. Each simulation was 5 ns in length and conducted in the NVE ensemble. |
244 |
|
|
245 |
|
|
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|
\section{Results and discussion} |