--- trunk/electrostaticMethodsPaper/SupportingInfo.tex 2006/03/23 15:03:33 2665 +++ trunk/electrostaticMethodsPaper/SupportingInfo.tex 2006/03/23 15:46:45 2666 @@ -1,5 +1,5 @@ %\documentclass[prb,aps,twocolumn,tabularx]{revtex4} -\documentclass[12pt]{article} +\documentclass[11pt]{article} %\usepackage{endfloat} \usepackage{amsmath} \usepackage{amssymb} @@ -24,21 +24,22 @@ studied methods with smooth particle-mesh Ewald. Each \begin{document} This document includes individual system-based comparisons of the -studied methods with smooth particle-mesh Ewald. 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. +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} -500 liquid state configurations were generated as described in the -Methods section 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 +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. +investigated. \begin{table}[htbp] \centering \caption{Regression results for the liquid water system. Tabulated @@ -137,47 +138,47 @@ For the most parts, the water results appear to parall \label{tab:spceAng} \end{table} -For the most parts, the water results appear to parallel the combined -results seen in the discussion in the main paper. There is good -agreement with 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. The results for both of these methods also -begin to decay as damping gets too large. +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 (PC) method performs poorly, as seen in the main -discussion section. In contrast to the combined values, however, the -use of a switching function and group based cutoffs really improves -the results for these neutral water molecules. The group switched -cutoff (GSC) shows mimics the energetics of SPME more poorly than the -{\sc sp} (with moderate damping) and {\sc sf} methods, but the -dynamics are quite good. The switching functions corrects -discontinuities in the potential and forces, leading to the improved -results. Such improvements with the use of a switching function has -been recognized in previous studies,\cite{Andrea83,Steinbach94} and it -is a useful tactic for stably incorporating local area electrostatic -effects. +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 really 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 corrects discontinuities in the potential and +forces, leading to these improved results. Such improvements with the +use of a switching function has 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 (RF) method simply extends the results observed in -the GSC case. Both methods are similar in form (i.e. neutral groups, -switching function), but RF incorporates an added effect from the -external dielectric. This similarity translates into the same good -dynamic results and improved energetic results. These still fall -short of the moderately damped {\sc sp} and {\sc sf} methods, but they -display how incorporating some implicit properties of the surroundings -(i.e. $\epsilon_\textrm{S}$) can improve results. +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. A final note for the liquid water system, use of group cutoffs and a -switching function also 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}). {\sc sp} shows significant -narrowing of the angle distribution in the cases with little to no -damping and only modest improvement for the ideal conditions ($\alpha$ -= 0.2 \AA${-1}$ and $R_\textrm{c} \geqslant 12$~\AA). The {\sc sf} -method simply shows modest narrowing across all damping and cutoff -ranges of interest. Group cutoffs and the switching function do -nothing for cases were error is introduced by overdamping the -potentials. +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$_\textrm{c}$} @@ -283,19 +284,19 @@ Highly ordered systems are a difficult test for the pa \label{tab:iceAng} \end{table} -Highly ordered systems are a difficult test for the pairwise systems -in that they lack the periodicity inherent to the Ewald summation. As -expected, the energy gap agreement with SPME reduces for the {\sc sp} -and {\sc sf} with parameters that were perfectly acceptable for the -disordered liquid system. Moving to higher $R_\textrm{c}$ remedies -this degraded performance, though at increase in computational cost. -However, 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. +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} reduces 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 RF exhibits a slightly improved energy -gap results over the liquid water system. One possible explanation is +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 @@ -305,13 +306,13 @@ pairwise summation methods in a highly charge disorder \section{\label{app:melt}NaCl Melt} A high temperature NaCl melt was tested to gauge the accuracy of the -pairwise summation methods in a highly charge disordered system. The -results for the energy gap comparisons and the force and torque vector +pairwise summation methods in a charged disordered system. The results +for the energy gap comparisons and the force and torque vector magnitude comparisons are shown in table \ref{tab:melt}. The force and torque vector directionality results are displayed separately in table \ref{tab:meltAng}, where the effect of group-based cutoffs and switching functions on the {\sc sp} and {\sc sf} potentials are -investigated. +investigated. \begin{table}[htbp] \centering @@ -470,17 +471,18 @@ method struggles in all cases with the exception of go {\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 +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 good long-time dynamics results observed for this -system. Since these results are a test of instantaneous dynamics, this -indicates that good long-time dynamics comes in part at the expense of +system. Since the data tabulated in table \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. Further indication of this comes from the full power spectra shown in the main text. It appears as though a -distortion is introduced between 200 to 300 cm$^{-1}$ with increased +distortion is introduced between 200 to 350 cm$^{-1}$ with increased $\alpha$. \section{\label{app:solnWeak}Weak NaCl Solution} @@ -595,16 +597,16 @@ This weak ionic strength system can be considered as a \label{tab:solnWeakAng} \end{table} -This weak ionic strength system can be considered as a perturbation of -the pure liquid water system. 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 visible for the {\sc rf} method. Though good force -reproduction is still maintained, the energy gaps show a significant -increase in the data scatter. This foreshadows the breakdown of the -method as we introduce system inhomogeneities. +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} @@ -614,7 +616,7 @@ results are displayed separately in table\ref{tab:soln 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 +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. @@ -712,10 +714,10 @@ configuration energy difference degrade to unuseable l \end{table} The {\sc rf} method struggles with the jump in ionic strength. The -configuration energy difference degrade to unuseable levels while the -forces and torques degrade in a more modest fashion. The {\sc rf} -method was designed for homogeneous systems, and this restriction is -apparent in these results. +configuration energy difference 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 @@ -831,7 +833,17 @@ This system appears not to show in any significant dev \label{tab:argonAng} \end{table} -This system appears not to show in any significant deviation in the previously observed results. The {\sc sp} and {\sc sf} methods give result qualities similar to those observed in section \ref{app:water}. The only significant difference is the improvement for 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, which the {\sc sp} and {\sc sf} methods explicity enforce, seems to play a greater role in the stability of the {\sc rf} method than the necessity of a homogeneous environment. +This system appears not to show in any significant deviation in the +previously observed results. The {\sc sp} and {\sc sf} methods give +result qualities similar to those observed in section +\ref{app:water}. The only significant difference is the improvement +for 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