--- trunk/electrostaticMethodsPaper/SupportingInfo.tex 2006/02/28 14:09:55 2599 +++ trunk/electrostaticMethodsPaper/SupportingInfo.tex 2006/03/24 02:39:59 2667 @@ -1,6 +1,6 @@ %\documentclass[prb,aps,twocolumn,tabularx]{revtex4} -\documentclass[12pt]{article} -\usepackage{endfloat} +\documentclass[11pt]{article} +%\usepackage{endfloat} \usepackage{amsmath} \usepackage{amssymb} \usepackage{epsf} @@ -23,13 +23,31 @@ This document includes system based comparisons of the \begin{document} -This document includes system based comparisons of the studied methods with smooth particle-mesh Ewald. Each of the seven systems comprises it's own section and has it's own discussion and tabular listing of the results for the $\Delta E$, force and torque vector magnitude, and force and torque vector direction comparisons. +This document includes individual system-based comparisons of the +studied methods with smooth particle mesh Ewald {\sc spme}. Each of +the seven systems comprises its own section and has its own discussion +and tabular listing of the results for the $\Delta E$, force and +torque vector magnitude, and force and torque vector direction +comparisons. -\section{\label{app-water}Liquid Water} +\section{\label{app:water}Liquid Water} +The first system considered was liquid water at 300K using the SPC/E +model of water.\cite{Berendsen87} The results for the energy gap +comparisons and the force and torque vector magnitude comparisons are +shown in table \ref{tab:spce}. The force and torque vector +directionality results are displayed separately in table +\ref{tab:spceAng}, where the effect of group-based cutoffs and +switching functions on the {\sc sp} and {\sc sf} potentials are +investigated. \begin{table}[htbp] \centering - \caption{Regression results for the liquid water system. Tabulated results include $\Delta E$ values (top set), force vector magnitudes (middle set) and torque vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx \infty$).} + \caption{Regression results for the liquid water system. Tabulated +results include $\Delta E$ values (top set), force vector magnitudes +(middle set) and torque vector magnitudes (bottom set). PC = Pure +Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group +Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx +\infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -49,10 +67,8 @@ RF & & 0.971 & 0.958 & 0.975 & 0.987 & 0.959 & 0. & 0.2 & 0.992 & 0.989 & 1.001 & 0.995 & 0.994 & 0.996 \\ & 0.3 & 0.984 & 0.980 & 0.996 & 0.985 & 0.982 & 0.987 \\ GSC & & 0.918 & 0.862 & 0.852 & 0.756 & 0.801 & 0.700 \\ -RF & & 0.971 & 0.958 & 0.975 & 0.987 & 0.959 & 0.983 \\ - +RF & & 0.971 & 0.958 & 0.975 & 0.987 & 0.959 & 0.983 \\ \midrule - PC & & -1.647 & 0.000 & -0.127 & 0.000 & -0.979 & 0.000 \\ SP & 0.0 & 0.735 & 0.368 & 0.813 & 0.537 & 0.865 & 0.659 \\ & 0.1 & 0.850 & 0.612 & 0.956 & 0.887 & 0.992 & 0.979 \\ @@ -64,9 +80,7 @@ RF & & 0.999 & 0.995 & 1.000 & 0.999 & 1.000 & 1. & 0.3 & 0.996 & 0.998 & 0.997 & 0.998 & 0.996 & 0.998 \\ GSC & & 0.998 & 0.995 & 1.000 & 0.999 & 1.000 & 1.000 \\ RF & & 0.999 & 0.995 & 1.000 & 0.999 & 1.000 & 1.000 \\ - \midrule - PC & & 2.387 & 0.000 & 0.183 & 0.000 & 1.282 & 0.000 \\ SP & 0.0 & 0.847 & 0.543 & 0.904 & 0.694 & 0.935 & 0.786 \\ & 0.1 & 0.922 & 0.749 & 0.980 & 0.934 & 0.996 & 0.988 \\ @@ -80,12 +94,17 @@ RF & & 0.993 & 0.989 & 0.998 & 0.996 & 1.000 & 0. RF & & 0.993 & 0.989 & 0.998 & 0.996 & 1.000 & 0.999 \\ \bottomrule \end{tabular} - \label{spceTabTMag} + \label{tab:spce} \end{table} \begin{table}[htbp] \centering - \caption{Variance results from Gaussian fits to angular distributions of the force and torque vectors in the liquid water system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} + \caption{Variance results from Gaussian fits to angular +distributions of the force and torque vectors in the liquid water +system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, +GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon +\approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = +Group Switched Shifted Force.} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -116,14 +135,70 @@ GSSF & 0.0 & 1.298 & 0.270 & 0.083 & 3.098 & 0.992 & & 0.3 & 0.728 & 0.694 & 0.692 & 7.410 & 6.942 & 6.748 \\ \bottomrule \end{tabular} - \label{spceTabAng} + \label{tab:spceAng} \end{table} -\section{\label{app-ice}Solid Water: Ice I$_\textrm{c}$} +The water results appear to parallel the combined results seen in the +discussion section of the main paper. There is good agreement with +{\sc spme} in both energetic and dynamic behavior when using the {\sc sf} +method with and without damping. The {\sc sp} method does well with an +$\alpha$ around 0.2 \AA$^{-1}$, particularly with cutoff radii greater +than 12 \AA. Overdamping the electrostatics reduces the agreement between both these methods and {\sc spme}. + +The pure cutoff ({\sc pc}) method performs poorly, again mirroring the +observations in the main portion of this paper. In contrast to the +combined values, however, the use of a switching function and group +based cutoffs greatly improves the results for these neutral water +molecules. The group switched cutoff ({\sc gsc}) does not mimic the +energetics of {\sc spme} as well as the {\sc sp} (with moderate +damping) and {\sc sf} methods, but the dynamics are quite good. The +switching functions correct discontinuities in the potential and +forces, leading to these improved results. Such improvements with the +use of a switching function have been recognized in previous +studies,\cite{Andrea83,Steinbach94} and this proves to be a useful +tactic for stably incorporating local area electrostatic effects. + +The reaction field ({\sc rf}) method simply extends upon the results +observed in the {\sc gsc} case. Both methods are similar in form +(i.e. neutral groups, switching function), but {\sc rf} incorporates +an added effect from the external dielectric. This similarity +translates into the same good dynamic results and improved energetic +agreement with {\sc spme}. Though this agreement is not to the level +of the moderately damped {\sc sp} and {\sc sf} methods, these results +show how incorporating some implicit properties of the surroundings +(i.e. $\epsilon_\textrm{S}$) can improve the solvent depiction. + +As a final note for the liquid water system, use of group cutoffs and a +switching function leads to noticeable improvements in the {\sc sp} +and {\sc sf} methods, primarily in directionality of the force and +torque vectors (table \ref{tab:spceAng}). The {\sc sp} method shows +significant narrowing of the angle distribution when using little to +no damping and only modest improvement for the recommended conditions +($\alpha$ = 0.2 \AA${-1}$ and $R_\textrm{c} \geqslant 12$~\AA). The +{\sc sf} method shows modest narrowing across all damping and cutoff +ranges of interest. When overdamping these methods, group cutoffs and +the switching function do not improve the force and torque +directionalities. +\section{\label{app:ice}Solid Water: Ice I$_\textrm{c}$} + +In addition to the disordered molecular system above, the ordered +molecular system of ice I$_\textrm{c}$ was also considered. The +results for the energy gap comparisons and the force and torque vector +magnitude comparisons are shown in table \ref{tab:ice}. The force and +torque vector directionality results are displayed separately in table +\ref{tab:iceAng}, where the effect of group-based cutoffs and +switching functions on the {\sc sp} and {\sc sf} potentials are +investigated. + \begin{table}[htbp] \centering - \caption{Regression results for the ice I$_\textrm{c}$ system. Tabulated results include $\Delta E$ values (top set), force vector magnitudes (middle set) and torque vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx \infty$).} + \caption{Regression results for the ice I$_\textrm{c}$ +system. Tabulated results include $\Delta E$ values (top set), force +vector magnitudes (middle set) and torque vector magnitudes (bottom +set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, +GSC = Group Switched Cutoff, and RF = Reaction Field (where +$\varepsilon \approx \infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -170,7 +245,7 @@ RF & & 0.994 & 0.997 & 0.997 & 0.999 & 1.000 & 1. RF & & 0.994 & 0.997 & 0.997 & 0.999 & 1.000 & 1.000 \\ \bottomrule \end{tabular} - \label{iceTab} + \label{tab:ice} \end{table} \begin{table}[htbp] @@ -206,11 +281,37 @@ GSSF & 0.0 & 2.124 & 0.132 & 0.069 & 0.919 & 0.263 & & 0.3 & 0.251 & 0.251 & 0.259 & 2.387 & 2.395 & 2.328 \\ \bottomrule \end{tabular} - \label{iceTabAng} + \label{tab:iceAng} \end{table} -\section{\label{app-melt}NaCl Melt} +Highly ordered systems are a difficult test for the pairwise methods +in that they lack the periodicity term of the Ewald summation. As +expected, the energy gap agreement with {\sc spme} is reduced for the +{\sc sp} and {\sc sf} methods with parameters that were acceptable for +the disordered liquid system. Moving to higher $R_\textrm{c}$ helps +improve the agreement, though at an increase in computational cost. +The dynamics of this crystalline system (both in magnitude and +direction) are little affected. Both methods still reproduce the Ewald +behavior with the same parameter recommendations from the previous +section. +It is also worth noting that {\sc rf} exhibits improved energy gap +results over the liquid water system. One possible explanation is +that the ice I$_\textrm{c}$ crystal is ordered such that the net +dipole moment of the crystal is zero. With $\epsilon_\textrm{S} = +\infty$, the reaction field incorporates this structural organization +by actively enforcing a zeroed dipole moment within each cutoff +sphere. + +\section{\label{app:melt}NaCl Melt} + +A high temperature NaCl melt was tested to gauge the accuracy of the +pairwise summation methods in a charged disordered system. The results +for the energy gap comparisons and the force vector magnitude +comparisons are shown in table \ref{tab:melt}. The force vector +directionality results are displayed separately in table +\ref{tab:meltAng}. + \begin{table}[htbp] \centering \caption{Regression results for the molten NaCl system. Tabulated results include $\Delta E$ values (top set) and force vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, and SF = Shifted Force.} @@ -224,27 +325,27 @@ SP & 0.0 & 0.937 & 0.996 & 0.880 & 0.995 & 0.971 & 0. Method & $\alpha$ & slope & $R^2$ & slope & $R^2$ & slope & $R^2$ \\ \midrule PC & & -0.008 & 0.000 & -0.049 & 0.005 & -0.136 & 0.020 \\ -SP & 0.0 & 0.937 & 0.996 & 0.880 & 0.995 & 0.971 & 0.999 \\ - & 0.1 & 1.004 & 0.999 & 0.958 & 1.000 & 0.928 & 0.994 \\ +SP & 0.0 & 0.928 & 0.996 & 0.931 & 0.998 & 0.950 & 0.999 \\ + & 0.1 & 0.977 & 0.998 & 0.998 & 1.000 & 0.997 & 1.000 \\ & 0.2 & 0.960 & 1.000 & 0.813 & 0.996 & 0.811 & 0.954 \\ & 0.3 & 0.671 & 0.994 & 0.439 & 0.929 & 0.535 & 0.831 \\ -SF & 0.0 & 1.001 & 1.000 & 0.949 & 1.000 & 1.008 & 1.000 \\ - & 0.1 & 1.025 & 1.000 & 0.960 & 1.000 & 0.929 & 0.994 \\ +SF & 0.0 & 0.996 & 1.000 & 0.995 & 1.000 & 0.997 & 1.000 \\ + & 0.1 & 1.021 & 1.000 & 1.024 & 1.000 & 1.007 & 1.000 \\ & 0.2 & 0.966 & 1.000 & 0.813 & 0.996 & 0.811 & 0.954 \\ & 0.3 & 0.671 & 0.994 & 0.439 & 0.929 & 0.535 & 0.831 \\ \midrule PC & & 1.103 & 0.000 & 0.989 & 0.000 & 0.802 & 0.000 \\ -SP & 0.0 & 0.976 & 0.983 & 1.001 & 0.991 & 0.985 & 0.995 \\ - & 0.1 & 0.996 & 0.997 & 0.997 & 0.998 & 0.996 & 0.996 \\ +SP & 0.0 & 0.973 & 0.981 & 0.975 & 0.988 & 0.979 & 0.992 \\ + & 0.1 & 0.987 & 0.992 & 0.993 & 0.998 & 0.997 & 0.999 \\ & 0.2 & 0.993 & 0.996 & 0.985 & 0.988 & 0.986 & 0.981 \\ & 0.3 & 0.956 & 0.956 & 0.940 & 0.912 & 0.948 & 0.929 \\ -SF & 0.0 & 0.997 & 0.998 & 0.995 & 0.999 & 0.999 & 1.000 \\ - & 0.1 & 1.001 & 0.997 & 0.997 & 0.999 & 0.996 & 0.996 \\ +SF & 0.0 & 0.996 & 0.997 & 0.997 & 0.999 & 0.998 & 1.000 \\ + & 0.1 & 1.000 & 0.997 & 1.001 & 0.999 & 1.000 & 1.000 \\ & 0.2 & 0.994 & 0.996 & 0.985 & 0.988 & 0.986 & 0.981 \\ & 0.3 & 0.956 & 0.956 & 0.940 & 0.912 & 0.948 & 0.929 \\ \bottomrule \end{tabular} - \label{meltTab} + \label{tab:melt} \end{table} \begin{table}[htbp] @@ -269,14 +370,35 @@ SF & 0.0 & 1.693 & 0.603 & 0.256 \\ & 0.3 & 23.734 & 67.305 & 57.252 \\ \bottomrule \end{tabular} - \label{meltTabAng} + \label{tab:meltAng} \end{table} -\section{\label{app-salt}NaCl Crystal} +The molten NaCl system shows more sensitivity to the electrostatic +damping than the water systems. The most noticeable point is that the +undamped {\sc sf} method does very well at replicating the {\sc spme} +configurational energy differences and forces. Light damping appears +to minimally improve the dynamics, but this comes with a deterioration +of the energy gap results. In contrast, this light damping improves +the {\sc sp} energy gaps and forces. Moderate and heavy electrostatic +damping reduce the agreement with {\sc spme} for both methods. From +these observations, the undamped {\sc sf} method is the best choice +for disordered systems of charges. +\section{\label{app:salt}NaCl Crystal} + +A 1000K NaCl crystal was used to investigate the accuracy of the +pairwise summation methods in an ordered system of charged +particles. The results for the energy gap comparisons and the force +vector magnitude comparisons are shown in table \ref{tab:salt}. The +force vector directionality results are displayed separately in table +\ref{tab:saltAng}. + \begin{table}[htbp] \centering - \caption{Regression results for the crystalline NaCl system. Tabulated results include $\Delta E$ values (top set) and force vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, and SF = Shifted Force.} + \caption{Regression results for the crystalline NaCl +system. Tabulated results include $\Delta E$ values (top set) and +force vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted +Potential, and SF = Shifted Force.} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -307,12 +429,16 @@ SF & 0.0 & 1.002 & 0.983 & 0.997 & 0.994 & 0.991 & 0. & 0.3 & 0.950 & 0.952 & 0.950 & 0.953 & 0.950 & 0.953 \\ \bottomrule \end{tabular} - \label{saltTab} + \label{tab:salt} \end{table} \begin{table}[htbp] \centering - \caption{Variance results from Gaussian fits to angular distributions of the force vectors in the crystalline NaCl system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx \infty$).} + \caption{Variance results from Gaussian fits to angular +distributions of the force vectors in the crystalline NaCl system. PC += Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group +Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx +\infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -332,14 +458,47 @@ SF & 0.0 & 10.025 & 3.555 & 1.648 \\ & 0.3 & 31.120 & 31.105 & 31.029 \\ \bottomrule \end{tabular} - \label{saltTabAng} + \label{tab:saltAng} \end{table} -\section{\label{app-sol1}Weak NaCl Solution} +The crystalline NaCl system is the most challenging test case for the +pairwise summation methods, as evidenced by the results in tables +\ref{tab:salt} and \ref{tab:saltAng}. The undamped and weakly damped +{\sc sf} methods with a 12 \AA\ cutoff radius seem to be the best +choices. These methods match well with {\sc spme} across the energy +gap, force magnitude, and force directionality tests. The {\sc sp} +method struggles in all cases, with the exception of good dynamics +reproduction when using weak electrostatic damping with a large cutoff +radius. +The moderate electrostatic damping case is not as good as we would +expect given the long-time dynamics results observed for this +system. Since the data tabulated in tables \ref{tab:salt} and +\ref{tab:saltAng} are a test of instantaneous dynamics, this indicates +that good long-time dynamics comes in part at the expense of +short-time dynamics. + +\section{\label{app:solnWeak}Weak NaCl Solution} + +In an effort to bridge the charged atomic and neutral molecular +systems, Na$^+$ and Cl$^-$ ion charge defects were incorporated into +the liquid water system. This low ionic strength system consists of 4 +ions in the 1000 SPC/E water solvent ($\approx$0.11 M). The results +for the energy gap comparisons and the force and torque vector +magnitude comparisons are shown in table \ref{tab:solnWeak}. The +force and torque vector directionality results are displayed +separately in table \ref{tab:solnWeakAng}, where the effect of +group-based cutoffs and switching functions on the {\sc sp} and {\sc +sf} potentials are investigated. + \begin{table}[htbp] \centering - \caption{Regression results for the weak NaCl solution system. Tabulated results include $\Delta E$ values (top set), force vector magnitudes (middle set) and torque vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} + \caption{Regression results for the weak NaCl solution +system. Tabulated results include $\Delta E$ values (top set), force +vector magnitudes (middle set) and torque vector magnitudes (bottom +set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, +GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon +\approx \infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -386,12 +545,17 @@ RF & & 0.984 & 0.975 & 0.996 & 0.995 & 0.998 & 0. RF & & 0.984 & 0.975 & 0.996 & 0.995 & 0.998 & 0.998 \\ \bottomrule \end{tabular} - \label{sol1Tab} + \label{tab:solnWeak} \end{table} \begin{table}[htbp] \centering - \caption{Variance results from Gaussian fits to angular distributions of the force and torque vectors in the weak NaCl solution system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} + \caption{Variance results from Gaussian fits to angular +distributions of the force and torque vectors in the weak NaCl +solution system. PC = Pure Cutoff, SP = Shifted Potential, SF = +Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where +$\varepsilon \approx \infty$), GSSP = Group Switched Shifted +Potential, and GSSF = Group Switched Shifted Force.} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -422,14 +586,40 @@ GSSF & 0.0 & 1.541 & 0.301 & 0.096 & 6.407 & 1.316 & & 0.3 & 0.954 & 0.759 & 0.780 & 12.337 & 7.684 & 7.849 \\ \bottomrule \end{tabular} - \label{sol1TabAng} + \label{tab:solnWeakAng} \end{table} -\section{\label{app-sol10}Strong NaCl Solution} +Because this system is a perturbation of the pure liquid water system, +comparisons are best drawn between these two sets. The {\sc sp} and +{\sc sf} methods are not significantly affected by the inclusion of a +few ions. The aspect of cutoff sphere neutralization aids in the +smooth incorporation of these ions; thus, all of the observations +regarding these methods carry over from section \ref{app:water}. The +differences between these systems are more visible for the {\sc rf} +method. Though good force agreement is still maintained, the energy +gaps show a significant increase in the data scatter. This foreshadows +the breakdown of the method as we introduce charged inhomogeneities. +\section{\label{app:solnStr}Strong NaCl Solution} + +The bridging of the charged atomic and neutral molecular systems was +further developed by considering a high ionic strength system +consisting of 40 ions in the 1000 SPC/E water solvent ($\approx$1.1 +M). The results for the energy gap comparisons and the force and +torque vector magnitude comparisons are shown in table +\ref{tab:solnStr}. The force and torque vector directionality +results are displayed separately in table \ref{tab:solnStrAng}, where +the effect of group-based cutoffs and switching functions on the {\sc +sp} and {\sc sf} potentials are investigated. + \begin{table}[htbp] \centering - \caption{Regression results for the strong NaCl solution system. Tabulated results include $\Delta E$ values (top set), force vector magnitudes (middle set) and torque vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx \infty$).} + \caption{Regression results for the strong NaCl solution +system. Tabulated results include $\Delta E$ values (top set), force +vector magnitudes (middle set) and torque vector magnitudes (bottom +set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, +GSC = Group Switched Cutoff, and RF = Reaction Field (where +$\varepsilon \approx \infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -476,7 +666,7 @@ RF & & 0.949 & 0.939 & 0.988 & 0.988 & 0.992 & 0. RF & & 0.949 & 0.939 & 0.988 & 0.988 & 0.992 & 0.993 \\ \bottomrule \end{tabular} - \label{sol10Tab} + \label{tab:solnStr} \end{table} \begin{table}[htbp] @@ -512,14 +702,39 @@ GSSF & 0.0 & 2.494 & 0.546 & 0.217 & 16.391 & 3.230 & & 0.3 & 1.752 & 1.454 & 1.451 & 23.587 & 14.390 & 14.245 \\ \bottomrule \end{tabular} - \label{sol10TabAng} + \label{tab:solnStrAng} \end{table} -\section{\label{app-argon}Argon Sphere in Water} +The {\sc rf} method struggles with the jump in ionic strength. The +configuration energy differences degrade to unusable levels while the +forces and torques show a more modest reduction in the agreement with +{\sc spme}. The {\sc rf} method was designed for homogeneous systems, +and this attribute is apparent in these results. +The {\sc sp} and {\sc sf} methods require larger cutoffs to maintain +their agreement with {\sc spme}. With these results, we still +recommend no to moderate damping for the {\sc sf} method and moderate +damping for the {\sc sp} method, both with cutoffs greater than 12 +\AA. + +\section{\label{app:argon}Argon Sphere in Water} + +The final model system studied was a 6 \AA\ sphere of Argon solvated +by SPC/E water. The results for the energy gap comparisons and the +force and torque vector magnitude comparisons are shown in table +\ref{tab:argon}. The force and torque vector directionality +results are displayed separately in table \ref{tab:argonAng}, where +the effect of group-based cutoffs and switching functions on the {\sc +sp} and {\sc sf} potentials are investigated. + \begin{table}[htbp] \centering - \caption{Regression results for the 6 \AA\ argon sphere in liquid water system. Tabulated results include $\Delta E$ values (top set), force vector magnitudes (middle set) and torque vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx \infty$).} + \caption{Regression results for the 6 \AA\ Argon sphere in liquid +water system. Tabulated results include $\Delta E$ values (top set), +force vector magnitudes (middle set) and torque vector magnitudes +(bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted +Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where +$\varepsilon \approx \infty$).} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -566,12 +781,17 @@ RF & & 0.993 & 0.988 & 0.997 & 0.995 & 0.999 & 0. RF & & 0.993 & 0.988 & 0.997 & 0.995 & 0.999 & 0.998 \\ \bottomrule \end{tabular} - \label{argonTab} + \label{tab:argon} \end{table} \begin{table}[htbp] \centering - \caption{Variance results from Gaussian fits to angular distributions of the force and torque vectors in the 6 \AA\ sphere of argon in liquid water system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} + \caption{Variance results from Gaussian fits to angular +distributions of the force and torque vectors in the 6 \AA\ sphere of +Argon in liquid water system. PC = Pure Cutoff, SP = Shifted +Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = +Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group +Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} \begin{tabular}{@{} ccrrrrrr @{}} \\ \toprule @@ -602,7 +822,24 @@ GSSF & 0.0 & 1.173 & 0.292 & 0.113 & 3.452 & 1.347 & & 0.3 & 0.814 & 0.825 & 0.816 & 8.325 & 8.447 & 8.132 \\ \bottomrule \end{tabular} - \label{argonTabAng} + \label{tab:argonAng} \end{table} -\end{document} \ No newline at end of file +This system does not appear to show any significant deviations from +the previously observed results. The {\sc sp} and {\sc sf} methods +have aggrements similar to those observed in section +\ref{app:water}. The only significant difference is the improvement +in the configuration energy differences for the {\sc rf} method. This +is surprising in that we are introducing an inhomogeneity to the +system; however, this inhomogeneity is charge-neutral and does not +result in charged cutoff spheres. The charge-neutrality of the cutoff +spheres, which the {\sc sp} and {\sc sf} methods explicitly enforce, +seems to play a greater role in the stability of the {\sc rf} method +than the required homogeneity of the environment. + +\newpage + +\bibliographystyle{jcp2} +\bibliography{electrostaticMethods} + +\end{document}