45 |
|
known low-pressure ice structures under all of these water models. |
46 |
|
Additionally, potential truncation was shown to have an effect on the |
47 |
|
calculated free energies, and can result in altered free energy |
48 |
< |
landscapes. Structure factor for the new crystal were generated and |
49 |
< |
we await experimental confirmation of the existence of this new |
50 |
< |
polymorph. |
48 |
> |
landscapes. Structure factor predictions for the new crystal were |
49 |
> |
generated and we await experimental confirmation of the existence of |
50 |
> |
this new polymorph. |
51 |
|
\end{abstract} |
52 |
|
|
53 |
|
%\narrowtext |
105 |
|
|
106 |
|
\begin{figure} |
107 |
|
\includegraphics[width=\linewidth]{unitCell.eps} |
108 |
< |
\caption{Unit cells for (A) Ice-{\it i} and (B) Ice-$i^\prime$, the |
109 |
< |
elongated variant of Ice-{\it i}. The spheres represent the |
108 |
> |
\caption{Unit cells for (A) Ice-{\it i} and (B) Ice-{\it i}$^\prime$, |
109 |
> |
the elongated variant of Ice-{\it i}. The spheres represent the |
110 |
|
center-of-mass locations of the water molecules. The $a$ to $c$ |
111 |
|
ratios for Ice-{\it i} and Ice-{\it i}$^\prime$ are given by |
112 |
|
$a:2.1214c$ and $a:1.7850c$ respectively.} |
138 |
|
from which Ice-{\it i} was crystallized (SSD/E) in addition to several |
139 |
|
common water models (TIP3P, TIP4P, TIP5P, and SPC/E) and a reaction |
140 |
|
field parametrized single point dipole water model (SSD/RF). It should |
141 |
< |
be noted that a second version of Ice-{\it i} (Ice-$i^\prime$) was |
142 |
< |
used in calculations involving SPC/E, TIP4P, and TIP5P. The unit cell |
143 |
< |
of this crystal (Fig. \ref{iceiCell}B) is similar to the Ice-{\it i} |
144 |
< |
unit it is extended in the direction of the (001) face and compressed |
145 |
< |
along the other two faces. |
141 |
> |
be noted that a second version of Ice-{\it i} (Ice-{\it i}$^\prime$) |
142 |
> |
was used in calculations involving SPC/E, TIP4P, and TIP5P. The unit |
143 |
> |
cell of this crystal (Fig. \ref{iceiCell}B) is similar to the Ice-{\it |
144 |
> |
i} unit it is extended in the direction of the (001) face and |
145 |
> |
compressed along the other two faces. There is typically a small |
146 |
> |
distortion of proton ordered Ice-{\it i}$^\prime$ that converts the |
147 |
> |
normally square tetramer into a rhombus with alternating approximately |
148 |
> |
85 and 95 degree angles. The degree of this distortion is model |
149 |
> |
dependent and significant enough to split the tetramer diagonal |
150 |
> |
location peak in the radial distribution function. |
151 |
|
|
152 |
|
\section{Methods} |
153 |
|
|
489 |
|
deposition environments, and in clathrate structures involving small |
490 |
|
non-polar molecules. Figs. \ref{fig:gofr} and \ref{fig:sofq} contain |
491 |
|
our predictions for both the pair distribution function ($g_{OO}(r)$) |
492 |
< |
and the structure factor ($S(\vec{q})$ for ice $I_c$ and for ice-{\it |
493 |
< |
i} at a temperature of 77K. In our initial comparison of the |
494 |
< |
predicted S(q) for Ice-{\it i} and experimental studies of amorphous |
495 |
< |
solid water, it is possible that some of the ``spurious'' peaks that |
496 |
< |
could not be assigned in an early report on high-density amorphous |
497 |
< |
(HDA) ice could correspond to peaks labeled in this |
498 |
< |
S(q).\cite{Bizid87} It should be noted that there is typically poor |
499 |
< |
agreement on crystal densities between simulation and experiment, so |
495 |
< |
such peak comparisons should be made with caution. We will leave it |
496 |
< |
to our experimental colleagues to make the final determination on |
497 |
< |
whether this ice polymorph is named appropriately (i.e. with an |
498 |
< |
imaginary number) or if it can be promoted to Ice-0. |
492 |
> |
and the structure factor ($S(\vec{q})$ for ice $I_h$, $I_c$, and for |
493 |
> |
ice-{\it i} at a temperature of 77K. In studies of the high and low |
494 |
> |
density forms of amorphous ice, ``spurious'' diffraction peaks have |
495 |
> |
been observed experimentally.\cite{Bizid87} It is possible that a |
496 |
> |
variant of Ice-{\it i} could explain some of this behavior; however, |
497 |
> |
we will leave it to our experimental colleagues to make the final |
498 |
> |
determination on whether this ice polymorph is named appropriately |
499 |
> |
(i.e. with an imaginary number) or if it can be promoted to Ice-0. |
500 |
|
|
501 |
|
\begin{figure} |
502 |
|
\includegraphics[width=\linewidth]{iceGofr.eps} |
503 |
< |
\caption{Radial distribution functions of Ice-{\it i} and ice $I_c$ |
504 |
< |
calculated from from simulations of the SSD/RF water model at 77 K.} |
503 |
> |
\caption{Radial distribution functions of ice $I_h$, $I_c$, |
504 |
> |
Ice-{\it i}, and Ice-{\it i}$^\prime$ calculated from from simulations |
505 |
> |
of the SSD/RF water model at 77 K.} |
506 |
|
\label{fig:gofr} |
507 |
|
\end{figure} |
508 |
|
|
509 |
|
\begin{figure} |
510 |
|
\includegraphics[width=\linewidth]{sofq.eps} |
511 |
< |
\caption{Predicted structure factors for Ice-{\it i} and ice $I_c$ at |
512 |
< |
77 K. The raw structure factors have been convoluted with a gaussian |
513 |
< |
instrument function (0.075 \AA$^{-1}$ width) to compensate for the |
514 |
< |
trunction effects in our finite size simulations. The labeled peaks |
515 |
< |
compared favorably with ``spurious'' peaks observed in experimental |
514 |
< |
studies of amorphous solid water.\cite{Bizid87}} |
511 |
> |
\caption{Predicted structure factors for ice $I_h$, $I_c$, Ice-{\it i}, |
512 |
> |
and Ice-{\it i}$^\prime$ at 77 K. The raw structure factors have |
513 |
> |
been convoluted with a gaussian instrument function (0.075 \AA$^{-1}$ |
514 |
> |
width) to compensate for the trunction effects in our finite size |
515 |
> |
simulations.} |
516 |
|
\label{fig:sofq} |
517 |
|
\end{figure} |
518 |
|
|