| 388 |
|
conditions, such as the density in fixed-volume simulations, can |
| 389 |
|
influence the polymorph expressed upon crystallization. |
| 390 |
|
|
| 391 |
< |
So what is the preferred solid polymorph for simulated water? The |
| 392 |
< |
answer appears to be dependent both on the conditions and the model |
| 393 |
< |
used. In the case of short cutoffs without a long-range interaction |
| 394 |
< |
correction, Ice-{\it i} and Ice-{\it i}$^\prime$ have the lowest free |
| 395 |
< |
energy of the studied polymorphs with all the models. Ideally, |
| 396 |
< |
crystallization of each model under constant pressure conditions, as |
| 397 |
< |
was done with SSD/E, would aid in the identification of their |
| 398 |
< |
respective preferred structures. This work, however, helps illustrate |
| 399 |
< |
how studies involving one specific model can lead to insight about |
| 400 |
< |
important behavior of others. In general, the above results support |
| 401 |
< |
the finding that the Ice-{\it i} polymorph is a stable crystal |
| 402 |
< |
structure that should be considered when studying the phase behavior |
| 403 |
< |
of water models. |
| 391 |
> |
\section{Conclusions} |
| 392 |
|
|
| 393 |
+ |
In this report, thermodynamic integration was used to determine the |
| 394 |
+ |
absolute free energies of several ice polymorphs. Of the studied |
| 395 |
+ |
crystal forms, Ice-{\it i} was observed to be the stable crystalline |
| 396 |
+ |
state for {\it all} the water models when using a 9.0 \AA\ |
| 397 |
+ |
intermolecular interaction cutoff. Through investigation of possible |
| 398 |
+ |
interaction truncation methods, the free energy was shown to be |
| 399 |
+ |
partially dependent on simulation conditions; however, Ice-{\it i} was |
| 400 |
+ |
still observered to be a stable polymorph of the studied water models. |
| 401 |
+ |
|
| 402 |
+ |
So what is the preferred solid polymorph for simulated water? As |
| 403 |
+ |
indicated above, the answer appears to be dependent both on the |
| 404 |
+ |
conditions and the model used. In the case of short cutoffs without a |
| 405 |
+ |
long-range interaction correction, Ice-{\it i} and Ice-{\it |
| 406 |
+ |
i}$^\prime$ have the lowest free energy of the studied polymorphs with |
| 407 |
+ |
all the models. Ideally, crystallization of each model under constant |
| 408 |
+ |
pressure conditions, as was done with SSD/E, would aid in the |
| 409 |
+ |
identification of their respective preferred structures. This work, |
| 410 |
+ |
however, helps illustrate how studies involving one specific model can |
| 411 |
+ |
lead to insight about important behavior of others. In general, the |
| 412 |
+ |
above results support the finding that the Ice-{\it i} polymorph is a |
| 413 |
+ |
stable crystal structure that should be considered when studying the |
| 414 |
+ |
phase behavior of water models. |
| 415 |
+ |
|
| 416 |
|
We also note that none of the water models used in this study are |
| 417 |
|
polarizable or flexible models. It is entirely possible that the |
| 418 |
|
polarizability of real water makes Ice-{\it i} substantially less |
