--- trunk/fennellDissertation/iceChapter.tex 2006/08/29 23:34:48 2981 +++ trunk/fennellDissertation/iceChapter.tex 2006/08/30 22:14:37 2986 @@ -8,12 +8,12 @@ available, it is only natural to compare the models un These models have been used to investigate important physical phenomena like phase transitions and the hydrophobic effect.\cite{Yamada02,Marrink94,Gallagher03} With the choice of models -available, it is only natural to compare the models under interesting +available, it is only natural to compare them under interesting thermodynamic conditions in an attempt to clarify the limitations of -each of the models.\cite{Jorgensen83,Jorgensen98b,Baez94,Mahoney01} -Two important property to quantify are the Gibbs and Helmholtz free -energies, particularly for the solid forms of water, as these predict -the thermodynamic stability of the various phases. Water has a +each.\cite{Jorgensen83,Jorgensen98b,Baez94,Mahoney01} Two important +property to quantify are the Gibbs and Helmholtz free energies, +particularly for the solid forms of water, as these predict the +thermodynamic stability of the various phases. Water has a particularly rich phase diagram and takes on a number of different and stable crystalline structures as the temperature and pressure are varied. This complexity makes it a challenging task to investigate the @@ -279,9 +279,9 @@ TIP3P & -11.41(2) & -11.23(3) & -11.82(3) & -12.30(3) \cmidrule(l){7-8} & \multicolumn{5}{c}{(kcal mol$^{-1}$)} & \multicolumn{2}{c}{(K)}\\ \midrule -TIP3P & -11.41(2) & -11.23(3) & -11.82(3) & -12.30(3) & - & 269(7) & 357(4)\\ -TIP4P & -11.84(3) & -12.04(2) & -12.08(3) & - & -12.33(3) & 262(6) & 354(4)\\ TIP5P & -11.85(3) & -11.86(2) & -11.96(2) & - & -12.29(2) & 266(7) & 337(4)\\ +TIP4P & -11.84(3) & -12.04(2) & -12.08(3) & - & -12.33(3) & 262(6) & 354(4)\\ +TIP3P & -11.41(2) & -11.23(3) & -11.82(3) & -12.30(3) & - & 269(7) & 357(4)\\ SPC/E & -12.87(2) & -13.05(2) & -13.26(3) & - & -13.55(2) & 299(6) & 396(4)\\ SSD/E & -11.27(2) & -11.19(4) & -12.09(2) & -12.54(2) & - & *355(4) & -\\ SSD/RF & -11.96(2) & -11.60(2) & -12.53(3) & -12.79(2) & - & 278(7) & 382(4)\\ @@ -403,7 +403,40 @@ influence the polymorph expressed upon crystallization \section{Expanded Results Using Damped Shifted Force Electrostatics} +In chapter \ref{chap:electrostatics}, we discussed in detail a +pairwise method for handling electrostatics (shifted force, {\sc sf}) +that can be used as a simple and efficient replacement for the Ewald +summation. Answering the question of the free energies of these ice +polymorphs with varying water models would be an interesting +application of this technique. To this end, we set up thermodynamic +integrations of all of the previously discussed ice polymorphs using +the {\sc sf} technique with a cutoff radius of 12~\AA\ and an $\alpha$ +of 0.2125~\AA . These calculations were performed on TIP5P-E and +TIP4P-Ew (variants of the root models optimized for the Ewald +summation) as well as SPC/E, SSD/RF, and TRED (see section +\ref{sec:tredWater}). +\begin{table} +\centering +\caption{HELMHOLTZ FREE ENERGIES OF ICE POLYMORPHS USING THE DAMPED +SHIFTED FORCE CORRECTION} +\begin{tabular}{ lccccc } +\toprule +\toprule +Model & I$_\textrm{h}$ & I$_\textrm{c}$ & B & Ice-$i$ & Ice-$i^\prime$ \\ +\cmidrule(lr){2-6} +& \multicolumn{5}{c}{(kcal mol$^{-1}$)} \\ +\midrule +TIP5P-E & -10.76(4) & -10.72(4) & & - & -10.68(4) \\ +TIP4P-Ew & & -11.77(3) & & - & -11.60(3) \\ +SPC/E & -12.98(3) & -11.60(3) & & - & -12.93(3) \\ +SSD/RF & -11.81(4) & -11.65(3) & & -12.41(4) & - \\ +TRED & -12.58(3) & -12.44(3) & & -13.09(4) & - \\ +\end{tabular} +\label{tab:dampedFreeEnergy} +\end{table} + + \section{Conclusions} In this work, thermodynamic integration was used to determine the