--- trunk/fennellDissertation/waterChapter.tex 2006/08/29 00:40:05 2979 +++ trunk/fennellDissertation/waterChapter.tex 2006/08/29 02:18:08 2980 @@ -458,7 +458,8 @@ correlation values below 0.5 and black areas have valu \begin{figure} \centering \includegraphics[width=2.5in]{./figures/corrDiag.pdf} -\caption{ An illustration of angles involved in the correlations observed in figure \ref{fig:contour}.} +\caption{ An illustration of angles involved in the correlations +observed in figure \ref{fig:contour}.} \label{fig:corrAngle} \end{figure} @@ -897,7 +898,8 @@ properties change. properties change. \begin{table} -\caption{PROPERTIES OF SSD/RF WHEN USING DIFFERENT ELECTROSTATIC CORRECTION METHODS} +\caption{PROPERTIES OF SSD/RF WHEN USING DIFFERENT ELECTROSTATIC +CORRECTION METHODS} \footnotesize \centering \begin{tabular}{ llccc } @@ -917,19 +919,41 @@ $\tau_2$ & (ps) & 3.2(2) & 2.45(7) & 2.3 \cite{Krynick \end{tabular} \label{tab:dampedSSDRF} \end{table} + +The properties shown in table \ref{tab:dampedSSDRF} compare +surprisingly well. The average density shows a modest increase when +using damped electrostatics in place of the reaction field. This comes +about because we neglect the pressure effect due to the surroundings +outside of the cuttoff, instead relying on screening effects to +neutralize electrostatic interactions at long distances. The $C_p$ +also shows a slight increase, indicating greater fluctuation in the +enthalpy at constant pressure. The only other differences between the +damped and reaction field results are the dipole reorientational time +constants, $\tau_1$ and $\tau_2$. When using damped electrostatics, +the water molecules relax more quickly and are almost identical to the +experimental values. These results indicate that not only is it +reasonable to use damped electrostatics with SSD/RF, it is recommended +if capturing realistic dynamics is of primary importance. This is an +encouraging result because of the more varied applicability of damping +over the reaction field technique. Rather than be limited to +homogeneous systems, SSD/RF can be used effectively with mixed +systems, such as dissolved ions, small organic molecules, or even +proteins. In addition to the properties tabulated in table -\ref{tab:dampedSSDRF}, we calculated the static dielectric constant +\ref{tab:dampedSSDRF}, we calculated the static dielectric constant from a 5ns simulation of SSD/RF using the damped electrostatics. The resulting value of 82.6(6) compares very favorably with the experimental value of 78.3.\cite{Malmberg56} This value is closer to the experimental value than what was expected according to figure \ref{fig:dielectricMap}, raising some questions as to the accuracy of -the visual contours in the figure. This simply enforces the -qualitative nature of contour plotting. +the visual contours in the figure. This highlights the qualitative +nature of contour plotting. \section{Tetrahedrally Restructured Elongated Dipole (TRED) Water Model} +The SSD/RF model works well with damped electrostatics, but because of its point multipole character, there is no charge neutralization correction at $R_\textrm{c}$. This has the effect of increasing the density, since there is no consideration of the ``surroundings''. + \begin{table} \caption{PROPERTIES OF TRED COMPARED WITH SSD/RF AND EXPERIMENT} \footnotesize @@ -940,15 +964,15 @@ $\rho$ & (g cm$^{-3}$) & 1.004(4) & 0.996(4) & 0.997 \ & & SSD/RF & TRED & Experiment [Ref.]\\ & & $\alpha = 0.2125$\AA$^{-1}$ & $\alpha = 0.2125$\AA$^{-1}$ & \\ \midrule -$\rho$ & (g cm$^{-3}$) & 1.004(4) & 0.996(4) & 0.997 \cite{CRC80}\\ -$C_p$ & (cal mol$^{-1}$ K$^{-1}$) & 27(1) & & 18.005 \cite{Wagner02} \\ +$\rho$ & (g cm$^{-3}$) & 1.004(4) & 0.995(5) & 0.997 \cite{CRC80}\\ +$C_p$ & (cal mol$^{-1}$ K$^{-1}$) & 27(1) & 23(1) & 18.005 \cite{Wagner02} \\ $D$ & ($10^{-5}$ cm$^2$ s$^{-1}$) & 2.33(2) & 2.30(5) & 2.299 \cite{Mills73}\\ $n_C$ & & 4.4 & 5.3 & 4.7 \cite{Hura00}\\ $n_H$ & & 3.7 & 4.1 & 3.5 \cite{Soper86}\\ $\tau_1$ & (ps) & 5.86(8) & 6.0(1) & 5.7 \cite{Eisenberg69}\\ $\tau_2$ & (ps) & 2.45(7) & 2.49(5) & 2.3 \cite{Krynicki66}\\ -$\epsilon_0$ & & 82.6(6) & & 78.3 \cite{Malmberg56}\\ -$\tau_D$ & (ps) & & & 8.2(4) \cite{Kindt96}\\ +$\epsilon_0$ & & 82.6(6) & 83(1) & 78.3 \cite{Malmberg56}\\ +$\tau_D$ & (ps) & 9.1(2) & 10.6(3) & 8.2(4) \cite{Kindt96}\\ \bottomrule \end{tabular} \label{tab:tredProps}