| 276 |
|
$I_h$, was investigated initially, but was found to be not as stable |
| 277 |
|
as proton disordered or antiferroelectric variants of ice $I_h$. The |
| 278 |
|
proton ordered variant of ice $I_h$ used here is a simple |
| 279 |
< |
antiferroelectric version that has an 8 molecule unit |
| 280 |
< |
cell.\cite{Davidson84} The crystals contained 648 or 1728 molecules |
| 281 |
< |
for ice B, 1024 or 1280 molecules for ice $I_h$, 1000 molecules for |
| 282 |
< |
ice $I_c$, or 1024 molecules for Ice-{\it i}. The larger crystal sizes |
| 283 |
< |
were necessary for simulations involving larger cutoff values. |
| 279 |
> |
antiferroelectric version that we divised, and it has an 8 molecule |
| 280 |
> |
unit cell similar to other predicted antiferroelectric $I_h$ |
| 281 |
> |
crystals.\cite{Davidson84} The crystals contained 648 or 1728 |
| 282 |
> |
molecules for ice B, 1024 or 1280 molecules for ice $I_h$, 1000 |
| 283 |
> |
molecules for ice $I_c$, or 1024 molecules for Ice-{\it i}. The larger |
| 284 |
> |
crystal sizes were necessary for simulations involving larger cutoff |
| 285 |
> |
values. |
| 286 |
|
|
| 287 |
|
\begin{table*} |
| 288 |
|
\begin{minipage}{\linewidth} |
| 297 |
|
\hline |
| 298 |
|
Water Model & $I_h$ & $I_c$ & B & Ice-{\it i}\\ |
| 299 |
|
\hline |
| 300 |
< |
TIP3P & -11.41(4) & -11.23(6) & -11.82(5) & -12.30(5)\\ |
| 301 |
< |
TIP4P & -11.84(5) & -12.04(4) & -12.08(6) & -12.33(6)\\ |
| 302 |
< |
TIP5P & -11.85(5) & -11.86(4) & -11.96(4) & -12.29(4)\\ |
| 303 |
< |
SPC/E & -12.67(3) & -12.96(3) & -13.25(5) & -13.55(3)\\ |
| 304 |
< |
SSD/E & -11.27(3) & -11.19(8) & -12.09(4) & -12.54(4)\\ |
| 305 |
< |
SSD/RF & -11.51(4) & NA* & -12.08(5) & -12.29(4)\\ |
| 300 |
> |
TIP3P & -11.41(2) & -11.23(3) & -11.82(3) & -12.30(3)\\ |
| 301 |
> |
TIP4P & -11.84(3) & -12.04(2) & -12.08(3) & -12.33(3)\\ |
| 302 |
> |
TIP5P & -11.85(3) & -11.86(2) & -11.96(2) & -12.29(2)\\ |
| 303 |
> |
SPC/E & -12.67(2) & -12.96(2) & -13.25(3) & -13.55(2)\\ |
| 304 |
> |
SSD/E & -11.27(2) & -11.19(4) & -12.09(2) & -12.54(2)\\ |
| 305 |
> |
SSD/RF & -11.51(2) & NA* & -12.08(3) & -12.29(2)\\ |
| 306 |
|
\end{tabular} |
| 307 |
|
\label{freeEnergy} |
| 308 |
|
\end{center} |
| 358 |
|
\hline |
| 359 |
|
Equilibria Point & TIP3P & TIP4P & TIP5P & SPC/E & SSD/E & SSD/RF & Exp.\\ |
| 360 |
|
\hline |
| 361 |
< |
$T_m$ (K) & 269(8) & 266(10) & 271(7) & 296(5) & - & 278(7) & 273\\ |
| 362 |
< |
$T_b$ (K) & 357(2) & 354(3) & 337(3) & 396(4) & - & 348(3) & 373\\ |
| 363 |
< |
$T_s$ (K) & - & - & - & - & 355(3) & - & -\\ |
| 361 |
> |
$T_m$ (K) & 269(4) & 266(5) & 271(4) & 296(3) & - & 278(4) & 273\\ |
| 362 |
> |
$T_b$ (K) & 357(2) & 354(2) & 337(2) & 396(2) & - & 348(2) & 373\\ |
| 363 |
> |
$T_s$ (K) & - & - & - & - & 355(2) & - & -\\ |
| 364 |
|
\end{tabular} |
| 365 |
|
\label{meltandboil} |
| 366 |
|
\end{center} |
| 431 |
|
for both the TIP3P and SPC/E water models; however, the narrowing of |
| 432 |
|
the free energy differences between the various solid forms is |
| 433 |
|
significant enough that it becomes less clear that it is the most |
| 434 |
< |
stable polymorph. The free energies of Ice-{\it i} and ice B overlap |
| 435 |
< |
within error, with ice $I_c$ just outside, indicating that Ice-{\it i} |
| 436 |
< |
might be metastable with respect to ice B and possibly ice $I_c$ in |
| 437 |
< |
the SPC/E water model. However, these results do not significantly |
| 438 |
< |
alter the finding that the Ice-{\it i} polymorph is a stable crystal |
| 439 |
< |
structure that should be considered when studying the phase behavior |
| 440 |
< |
of water models. |
| 434 |
> |
stable polymorph with the SPC/E model. The free energies of Ice-{\it |
| 435 |
> |
i} and ice B nearly overlap within error, with ice $I_c$ just outside |
| 436 |
> |
as well, indicating that Ice-{\it i} might be metastable with respect |
| 437 |
> |
to ice B and possibly ice $I_c$ with SPC/E. However, these results do |
| 438 |
> |
not significantly alter the finding that the Ice-{\it i} polymorph is |
| 439 |
> |
a stable crystal structure that should be considered when studying the |
| 440 |
> |
phase behavior of water models. |
| 441 |
|
|
| 442 |
|
\begin{table*} |
| 443 |
|
\begin{minipage}{\linewidth} |
| 450 |
|
\hline |
| 451 |
|
\ \ Water Model \ \ & \ \ \ \ \ $I_h$ \ \ & \ \ \ \ \ $I_c$ \ \ & \ \quad \ \ \ \ B \ \ & \ \ \ \ \ Ice-{\it i} \ \ \\ |
| 452 |
|
\hline |
| 453 |
< |
TIP3P & -11.53(4) & -11.24(6) & -11.51(5) & -11.67(5)\\ |
| 454 |
< |
SPC/E & -12.77(3) & -12.92(3) & -12.96(5) & -13.02(3)\\ |
| 453 |
> |
TIP3P & -11.53(2) & -11.24(3) & -11.51(3) & -11.67(3)\\ |
| 454 |
> |
SPC/E & -12.77(2) & -12.92(2) & -12.96(3) & -13.02(2)\\ |
| 455 |
|
\end{tabular} |
| 456 |
|
\label{pmeShift} |
| 457 |
|
\end{center} |
