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%\documentclass[prb,aps,twocolumn,tabularx]{revtex4} |
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\documentclass[12pt]{article} |
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\usepackage{endfloat} |
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%\usepackage{endfloat} |
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\usepackage{amsmath} |
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\usepackage{amssymb} |
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\usepackage{epsf} |
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\begin{document} |
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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. |
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This document includes individual system-based comparisons of the |
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studied methods with smooth particle-mesh Ewald. Each of the seven |
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systems comprises its own section and has its own discussion and |
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tabular listing of the results for the $\Delta E$, force and torque |
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vector magnitude, and force and torque vector direction comparisons. |
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\section{\label{app-water}Liquid Water} |
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\section{\label{app:water}Liquid Water} |
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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:spceTabTMag}. |
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500 liquid state configurations were generated as described in the |
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Methods section using the SPC/E model of water.\cite{Berendsen87} The |
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results for the energy gap comparisons and the force and torque vector |
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magnitude comparisons are shown in table \ref{tab:spce}. The force |
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and torque vector directionality results are displayed separately in |
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table \ref{tab:spceAng}, where the effect of group-based cutoffs and |
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switching functions on the {\sc sp} and {\sc sf} potentials are |
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investigated. |
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\begin{table}[htbp] |
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\centering |
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\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 $\varepsilon \approx \infty$).} |
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\caption{Regression results for the liquid water system. Tabulated |
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results include $\Delta E$ values (top set), force vector magnitudes |
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(middle set) and torque vector magnitudes (bottom set). PC = Pure |
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Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group |
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Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx |
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\infty$).} |
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\begin{tabular}{@{} ccrrrrrr @{}} |
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\\ |
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\toprule |
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& 0.2 & 0.992 & 0.989 & 1.001 & 0.995 & 0.994 & 0.996 \\ |
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& 0.3 & 0.984 & 0.980 & 0.996 & 0.985 & 0.982 & 0.987 \\ |
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GSC & & 0.918 & 0.862 & 0.852 & 0.756 & 0.801 & 0.700 \\ |
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RF & & 0.971 & 0.958 & 0.975 & 0.987 & 0.959 & 0.983 \\ |
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RF & & 0.971 & 0.958 & 0.975 & 0.987 & 0.959 & 0.983 \\ |
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\midrule |
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|
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PC & & -1.647 & 0.000 & -0.127 & 0.000 & -0.979 & 0.000 \\ |
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SP & 0.0 & 0.735 & 0.368 & 0.813 & 0.537 & 0.865 & 0.659 \\ |
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& 0.1 & 0.850 & 0.612 & 0.956 & 0.887 & 0.992 & 0.979 \\ |
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& 0.3 & 0.996 & 0.998 & 0.997 & 0.998 & 0.996 & 0.998 \\ |
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GSC & & 0.998 & 0.995 & 1.000 & 0.999 & 1.000 & 1.000 \\ |
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RF & & 0.999 & 0.995 & 1.000 & 0.999 & 1.000 & 1.000 \\ |
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|
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\midrule |
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– |
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PC & & 2.387 & 0.000 & 0.183 & 0.000 & 1.282 & 0.000 \\ |
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SP & 0.0 & 0.847 & 0.543 & 0.904 & 0.694 & 0.935 & 0.786 \\ |
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& 0.1 & 0.922 & 0.749 & 0.980 & 0.934 & 0.996 & 0.988 \\ |
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RF & & 0.993 & 0.989 & 0.998 & 0.996 & 1.000 & 0.999 \\ |
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\bottomrule |
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\end{tabular} |
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\label{tab:spceTabTMag} |
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\label{tab:spce} |
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\end{table} |
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|
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Unless there is a significant change in result in any of the further systems, we are going to neglect to comment on the pure cutoff (PC) system. It is unreasonable to expect it to perform well in either energetic or dynamic studies using molecular groups, as evidenced in previous studies and in the results displayed here and in the rest of this paper.\cite{Adams79,Steinbach94} In contrast to PC, the {\sc sp} method shows variety in the results. In the weakly and undamped cases, the results are poor for both the energy gap and dynamics, and this is not surprising considering the energy oscillations observed by Wolf {\it et al.} and the discontinuity in the forces discussed in the main portion of this paper.\cite{Wolf99} Long cutoff radii, moderate damping, or a combination of the two are required for {\sc sp} to perform respectably. With a cutoff greater than 12 \AA\ and $\alpha$ of 0.2 \AA$^{-1}$, {\sc sp} provides result right in line with SPME. |
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The {\sc sf} method displays energetic and dynamic results very similar to SPME under undamped to moderately damped conditions. The quality seems to degrade in the overdamped case ($\alpha = 0.3 \AA^{-1}$) to values identical to {\sc sp}, so it is important not to get carried away with the use of damping. A cutoff radius choice of 12 \AA\ or higher is recommended, primarily due to the energy gap results of interest in Monte Carlo (MC) calculations. |
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The group switched cutoff (GSC) and reaction field (RF) methods seem to have very similar behavior, with the preference given to RF for the improved energy gap results. Neither mimics the energetics of SPME as well as the {\sc sp} (with moderate damping) and {\sc sf} methods, and the results seem relatively independent of cutoff radius. The dynamics for both methods, however, are quite good. Both methods utilize switching functions, which correct and discontinuities in the potential and forces, a possible reason for the improved results. It is interesting to compare the PC with the GSC cases, and recognize the significant improvement that group based cutoffs and switching functions provide. This as been recognized in previous studies,\cite{Andrea83,Steinbach94} and is a useful tactic for stably incorporating local area electrostatic effects. |
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|
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\begin{table}[htbp] |
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\centering |
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\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.} |
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\caption{Variance results from Gaussian fits to angular |
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distributions of the force and torque vectors in the liquid water |
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system. PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, |
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GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon |
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\approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = |
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Group Switched Shifted Force.} |
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\begin{tabular}{@{} ccrrrrrr @{}} |
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\\ |
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\toprule |
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& 0.3 & 0.728 & 0.694 & 0.692 & 7.410 & 6.942 & 6.748 \\ |
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\bottomrule |
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\end{tabular} |
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\label{tab:spceTabAng} |
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\label{tab:spceAng} |
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\end{table} |
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|
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\section{\label{app-ice}Solid Water: Ice I$_\textrm{c}$} |
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For the most parts, the water results appear to parallel the combined |
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results seen in the discussion in the main paper. There is good |
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agreement with SPME in both energetic and dynamic behavior when using |
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the {\sc sf} method with and without damping. The {\sc sp} method does |
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well with an $\alpha$ around 0.2 \AA$^{-1}$, particularly with cutoff |
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radii greater than 12 \AA. The results for both of these methods also |
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begin to decay as damping gets too large. |
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|
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The pure cutoff (PC) method performs poorly, as seen in the main |
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discussion section. In contrast to the combined values, however, the |
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use of a switching function and group based cutoffs really improves |
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the results for these neutral water molecules. The group switched |
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cutoff (GSC) shows mimics the energetics of SPME more poorly than the |
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{\sc sp} (with moderate damping) and {\sc sf} methods, but the |
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dynamics are quite good. The switching functions corrects |
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discontinuities in the potential and forces, leading to the improved |
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results. Such improvements with the use of a switching function has |
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been recognized in previous studies,\cite{Andrea83,Steinbach94} and it |
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is a useful tactic for stably incorporating local area electrostatic |
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effects. |
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|
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The reaction field (RF) method simply extends the results observed in |
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the GSC case. Both methods are similar in form (i.e. neutral groups, |
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switching function), but RF incorporates an added effect from the |
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external dielectric. This similarity translates into the same good |
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dynamic results and improved energetic results. These still fall |
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short of the moderately damped {\sc sp} and {\sc sf} methods, but they |
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display how incorporating some implicit properties of the surroundings |
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(i.e. $\epsilon_\textrm{S}$) can improve results. |
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|
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A final note for the liquid water system, use of group cutoffs and a |
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switching function also leads to noticeable improvements in the {\sc |
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sp} and {\sc sf} methods, primarily in directionality of the force and |
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torque vectors (table \ref{tab:spceAng}). {\sc sp} shows significant |
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narrowing of the angle distribution in the cases with little to no |
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damping and only modest improvement for the ideal conditions ($\alpha$ |
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= 0.2 \AA${-1}$ and $R_\textrm{c} \geqslant 12$~\AA). The {\sc sf} |
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method simply shows modest narrowing across all damping and cutoff |
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ranges of interest. Group cutoffs and the switching function do |
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nothing for cases were error is introduced by overdamping the |
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potentials. |
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|
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\section{\label{app:ice}Solid Water: Ice I$_\textrm{c}$} |
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|
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In addition to the disordered molecular system above, the ordered |
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molecular system of ice I$_\textrm{c}$ was also considered. The |
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results for the energy gap comparisons and the force and torque vector |
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magnitude comparisons are shown in table \ref{tab:ice}. The force and |
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torque vector directionality results are displayed separately in table |
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\ref{tab:iceAng}, where the effect of group-based cutoffs and |
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switching functions on the {\sc sp} and {\sc sf} potentials are |
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investigated. |
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|
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\begin{table}[htbp] |
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\centering |
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\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 $\varepsilon \approx \infty$).} |
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\caption{Regression results for the ice I$_\textrm{c}$ |
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system. Tabulated results include $\Delta E$ values (top set), force |
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vector magnitudes (middle set) and torque vector magnitudes (bottom |
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set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, |
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GSC = Group Switched Cutoff, and RF = Reaction Field (where |
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$\varepsilon \approx \infty$).} |
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\begin{tabular}{@{} ccrrrrrr @{}} |
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\\ |
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\toprule |
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RF & & 0.994 & 0.997 & 0.997 & 0.999 & 1.000 & 1.000 \\ |
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\bottomrule |
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\end{tabular} |
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\label{tab:iceTab} |
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\label{tab:ice} |
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\end{table} |
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|
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\begin{table}[htbp] |
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& 0.3 & 0.251 & 0.251 & 0.259 & 2.387 & 2.395 & 2.328 \\ |
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\bottomrule |
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\end{tabular} |
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\label{tab:iceTabAng} |
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\label{tab:iceAng} |
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\end{table} |
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|
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\section{\label{app-melt}NaCl Melt} |
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Highly ordered systems are a difficult test for the pairwise systems |
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in that they lack the periodicity inherent to the Ewald summation. As |
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expected, the energy gap agreement with SPME reduces for the {\sc sp} |
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and {\sc sf} with parameters that were perfectly acceptable for the |
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disordered liquid system. Moving to higher $R_\textrm{c}$ remedies |
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this degraded performance, though at increase in computational cost. |
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However, the dynamics of this crystalline system (both in magnitude |
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and direction) are little affected. Both methods still reproduce the |
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Ewald behavior with the same parameter recommendations from the |
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previous section. |
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|
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It is also worth noting that RF exhibits a slightly improved energy |
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gap results over the liquid water system. One possible explanation is |
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that the ice I$_\textrm{c}$ crystal is ordered such that the net |
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dipole moment of the crystal is zero. With $\epsilon_\textrm{S} = |
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\infty$, the reaction field incorporates this structural organization |
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by actively enforcing a zeroed dipole moment within each cutoff |
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sphere. |
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|
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\section{\label{app:melt}NaCl Melt} |
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|
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A high temperature NaCl melt was tested to gauge the accuracy of the |
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pairwise summation methods in a highly charge disordered system. The |
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results for the energy gap comparisons and the force and torque vector |
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magnitude comparisons are shown in table \ref{tab:melt}. The force |
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and torque vector directionality results are displayed separately in |
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table \ref{tab:meltAng}, where the effect of group-based cutoffs and |
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switching functions on the {\sc sp} and {\sc sf} potentials are |
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investigated. |
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|
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\begin{table}[htbp] |
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\centering |
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\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.} |
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Method & $\alpha$ & slope & $R^2$ & slope & $R^2$ & slope & $R^2$ \\ |
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\midrule |
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PC & & -0.008 & 0.000 & -0.049 & 0.005 & -0.136 & 0.020 \\ |
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SP & 0.0 & 0.937 & 0.996 & 0.880 & 0.995 & 0.971 & 0.999 \\ |
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& 0.1 & 1.004 & 0.999 & 0.958 & 1.000 & 0.928 & 0.994 \\ |
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SP & 0.0 & 0.928 & 0.996 & 0.931 & 0.998 & 0.950 & 0.999 \\ |
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& 0.1 & 0.977 & 0.998 & 0.998 & 1.000 & 0.997 & 1.000 \\ |
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& 0.2 & 0.960 & 1.000 & 0.813 & 0.996 & 0.811 & 0.954 \\ |
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& 0.3 & 0.671 & 0.994 & 0.439 & 0.929 & 0.535 & 0.831 \\ |
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SF & 0.0 & 1.001 & 1.000 & 0.949 & 1.000 & 1.008 & 1.000 \\ |
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& 0.1 & 1.025 & 1.000 & 0.960 & 1.000 & 0.929 & 0.994 \\ |
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SF & 0.0 & 0.996 & 1.000 & 0.995 & 1.000 & 0.997 & 1.000 \\ |
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& 0.1 & 1.021 & 1.000 & 1.024 & 1.000 & 1.007 & 1.000 \\ |
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& 0.2 & 0.966 & 1.000 & 0.813 & 0.996 & 0.811 & 0.954 \\ |
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& 0.3 & 0.671 & 0.994 & 0.439 & 0.929 & 0.535 & 0.831 \\ |
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\midrule |
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PC & & 1.103 & 0.000 & 0.989 & 0.000 & 0.802 & 0.000 \\ |
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SP & 0.0 & 0.976 & 0.983 & 1.001 & 0.991 & 0.985 & 0.995 \\ |
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& 0.1 & 0.996 & 0.997 & 0.997 & 0.998 & 0.996 & 0.996 \\ |
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SP & 0.0 & 0.973 & 0.981 & 0.975 & 0.988 & 0.979 & 0.992 \\ |
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& 0.1 & 0.987 & 0.992 & 0.993 & 0.998 & 0.997 & 0.999 \\ |
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& 0.2 & 0.993 & 0.996 & 0.985 & 0.988 & 0.986 & 0.981 \\ |
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& 0.3 & 0.956 & 0.956 & 0.940 & 0.912 & 0.948 & 0.929 \\ |
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SF & 0.0 & 0.997 & 0.998 & 0.995 & 0.999 & 0.999 & 1.000 \\ |
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& 0.1 & 1.001 & 0.997 & 0.997 & 0.999 & 0.996 & 0.996 \\ |
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SF & 0.0 & 0.996 & 0.997 & 0.997 & 0.999 & 0.998 & 1.000 \\ |
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& 0.1 & 1.000 & 0.997 & 1.001 & 0.999 & 1.000 & 1.000 \\ |
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|
& 0.2 & 0.994 & 0.996 & 0.985 & 0.988 & 0.986 & 0.981 \\ |
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& 0.3 & 0.956 & 0.956 & 0.940 & 0.912 & 0.948 & 0.929 \\ |
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\bottomrule |
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|
\end{tabular} |
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\label{tab:meltTab} |
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> |
\label{tab:melt} |
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|
\end{table} |
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|
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|
\begin{table}[htbp] |
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& 0.3 & 23.734 & 67.305 & 57.252 \\ |
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\bottomrule |
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\end{tabular} |
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\label{tab:meltTabAng} |
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\label{tab:meltAng} |
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|
\end{table} |
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|
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\section{\label{app-salt}NaCl Crystal} |
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The molten NaCl system shows more sensitivity to the electrostatic |
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damping than the water systems. The most noticeable point is that the |
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undamped {\sc sf} method does very well at replicating the {\sc spme} |
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configurational energy differences and forces. Light damping appears |
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to minimally improve the dynamics, but this comes with a deterioration |
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of the energy gap results. In contrast, this light damping improves |
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the {\sc sp} energy gaps and forces. Moderate and heavy electrostatic |
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damping reduce the agreement with {\sc spme} for both methods. From |
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these observations, the undamped {\sc sf} method is the best choice |
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for disordered systems of charges. |
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|
|
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\section{\label{app:salt}NaCl Crystal} |
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|
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A 1000K NaCl crystal was used to investigate the accuracy of the |
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pairwise summation methods in an ordered system of charged |
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particles. The results for the energy gap comparisons and the force |
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and torque vector magnitude comparisons are shown in table |
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+ |
\ref{tab:salt}. The force and torque vector directionality results |
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+ |
are displayed separately in table \ref{tab:saltAng}, where the effect |
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+ |
of group-based cutoffs and switching functions on the {\sc sp} and |
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{\sc sf} potentials are investigated. |
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|
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|
\begin{table}[htbp] |
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\centering |
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< |
\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.} |
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> |
\caption{Regression results for the crystalline NaCl |
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> |
system. Tabulated results include $\Delta E$ values (top set) and |
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> |
force vector magnitudes (bottom set). PC = Pure Cutoff, SP = Shifted |
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> |
Potential, and SF = Shifted Force.} |
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|
\begin{tabular}{@{} ccrrrrrr @{}} |
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\\ |
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|
\toprule |
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|
& 0.3 & 0.950 & 0.952 & 0.950 & 0.953 & 0.950 & 0.953 \\ |
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|
\bottomrule |
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|
\end{tabular} |
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< |
\label{tab:saltTab} |
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> |
\label{tab:salt} |
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|
\end{table} |
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|
|
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|
\begin{table}[htbp] |
| 439 |
|
\centering |
| 440 |
< |
\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 $\varepsilon \approx \infty$).} |
| 440 |
> |
\caption{Variance results from Gaussian fits to angular |
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> |
distributions of the force vectors in the crystalline NaCl system. PC |
| 442 |
> |
= Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, GSC = Group |
| 443 |
> |
Switched Cutoff, and RF = Reaction Field (where $\varepsilon \approx |
| 444 |
> |
\infty$).} |
| 445 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 446 |
|
\\ |
| 447 |
|
\toprule |
| 461 |
|
& 0.3 & 31.120 & 31.105 & 31.029 \\ |
| 462 |
|
\bottomrule |
| 463 |
|
\end{tabular} |
| 464 |
< |
\label{tab:saltTabAng} |
| 464 |
> |
\label{tab:saltAng} |
| 465 |
|
\end{table} |
| 466 |
|
|
| 467 |
< |
\section{\label{app-sol1}Weak NaCl Solution} |
| 467 |
> |
The crystalline NaCl system is the most challenging test case for the |
| 468 |
> |
pairwise summation methods, as evidenced by the results in tables |
| 469 |
> |
\ref{tab:salt} and \ref{tab:saltAng}. The undamped and weakly damped |
| 470 |
> |
{\sc sf} methods with a 12 \AA\ cutoff radius seem to be the best |
| 471 |
> |
choices. These methods match well with {\sc spme} across the energy |
| 472 |
> |
gap, force magnitude, and force directionality tests. The {\sc sp} |
| 473 |
> |
method struggles in all cases with the exception of good dynamics |
| 474 |
> |
reproduction when using weak electrostatic damping with a large cutoff |
| 475 |
> |
radius. |
| 476 |
|
|
| 477 |
+ |
The moderate electrostatic damping case is not as good as we would |
| 478 |
+ |
expect given the good long-time dynamics results observed for this |
| 479 |
+ |
system. Since these results are a test of instantaneous dynamics, this |
| 480 |
+ |
indicates that good long-time dynamics comes in part at the expense of |
| 481 |
+ |
short-time dynamics. Further indication of this comes from the full |
| 482 |
+ |
power spectra shown in the main text. It appears as though a |
| 483 |
+ |
distortion is introduced between 200 to 300 cm$^{-1}$ with increased |
| 484 |
+ |
$\alpha$. |
| 485 |
+ |
|
| 486 |
+ |
\section{\label{app:solnWeak}Weak NaCl Solution} |
| 487 |
+ |
|
| 488 |
+ |
In an effort to bridge the charged atomic and neutral molecular |
| 489 |
+ |
systems, Na$^+$ and Cl$^-$ ion charge defects were incorporated into |
| 490 |
+ |
the liquid water system. This low ionic strength system consists of 4 |
| 491 |
+ |
ions in the 1000 SPC/E water solvent ($\approx$0.11 M). The results |
| 492 |
+ |
for the energy gap comparisons and the force and torque vector |
| 493 |
+ |
magnitude comparisons are shown in table \ref{tab:solnWeak}. The |
| 494 |
+ |
force and torque vector directionality results are displayed |
| 495 |
+ |
separately in table \ref{tab:solnWeakAng}, where the effect of |
| 496 |
+ |
group-based cutoffs and switching functions on the {\sc sp} and {\sc |
| 497 |
+ |
sf} potentials are investigated. |
| 498 |
+ |
|
| 499 |
|
\begin{table}[htbp] |
| 500 |
|
\centering |
| 501 |
< |
\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.} |
| 501 |
> |
\caption{Regression results for the weak NaCl solution |
| 502 |
> |
system. Tabulated results include $\Delta E$ values (top set), force |
| 503 |
> |
vector magnitudes (middle set) and torque vector magnitudes (bottom |
| 504 |
> |
set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, |
| 505 |
> |
GSC = Group Switched Cutoff, RF = Reaction Field (where $\varepsilon |
| 506 |
> |
\approx \infty$), GSSP = Group Switched Shifted Potential, and GSSF = |
| 507 |
> |
Group Switched Shifted Force.} |
| 508 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 509 |
|
\\ |
| 510 |
|
\toprule |
| 551 |
|
RF & & 0.984 & 0.975 & 0.996 & 0.995 & 0.998 & 0.998 \\ |
| 552 |
|
\bottomrule |
| 553 |
|
\end{tabular} |
| 554 |
< |
\label{tab:sol1Tab} |
| 554 |
> |
\label{tab:solnWeak} |
| 555 |
|
\end{table} |
| 556 |
|
|
| 557 |
|
\begin{table}[htbp] |
| 558 |
|
\centering |
| 559 |
< |
\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.} |
| 559 |
> |
\caption{Variance results from Gaussian fits to angular |
| 560 |
> |
distributions of the force and torque vectors in the weak NaCl |
| 561 |
> |
solution system. PC = Pure Cutoff, SP = Shifted Potential, SF = |
| 562 |
> |
Shifted Force, GSC = Group Switched Cutoff, RF = Reaction Field (where |
| 563 |
> |
$\varepsilon \approx \infty$), GSSP = Group Switched Shifted |
| 564 |
> |
Potential, and GSSF = Group Switched Shifted Force.} |
| 565 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 566 |
|
\\ |
| 567 |
|
\toprule |
| 592 |
|
& 0.3 & 0.954 & 0.759 & 0.780 & 12.337 & 7.684 & 7.849 \\ |
| 593 |
|
\bottomrule |
| 594 |
|
\end{tabular} |
| 595 |
< |
\label{tab:sol1TabAng} |
| 595 |
> |
\label{tab:solnWeakAng} |
| 596 |
|
\end{table} |
| 597 |
|
|
| 598 |
< |
\section{\label{app-sol10}Strong NaCl Solution} |
| 598 |
> |
This weak ionic strength system can be considered as a perturbation of |
| 599 |
> |
the pure liquid water system. The {\sc sp} and {\sc sf} methods are |
| 600 |
> |
not significantly affected by the inclusion of a few ions. The aspect |
| 601 |
> |
of cutoff sphere neutralization aids in the smooth incorporation of |
| 602 |
> |
these ions; thus, all of the observations regarding these methods |
| 603 |
> |
carry over from section \ref{app:water}. The differences between these |
| 604 |
> |
systems are visible for the {\sc rf} method. Though good force |
| 605 |
> |
reproduction is still maintained, the energy gaps show a significant |
| 606 |
> |
increase in the data scatter. This foreshadows the breakdown of the |
| 607 |
> |
method as we introduce system inhomogeneities. |
| 608 |
|
|
| 609 |
+ |
\section{\label{app:solnStr}Strong NaCl Solution} |
| 610 |
+ |
|
| 611 |
+ |
The bridging of the charged atomic and neutral molecular systems was |
| 612 |
+ |
further developed by considering a high ionic strength system |
| 613 |
+ |
consisting of 40 ions in the 1000 SPC/E water solvent ($\approx$1.1 |
| 614 |
+ |
M). The results for the energy gap comparisons and the force and |
| 615 |
+ |
torque vector magnitude comparisons are shown in table |
| 616 |
+ |
\ref{tab:solnWeak}. The force and torque vector directionality |
| 617 |
+ |
results are displayed separately in table\ref{tab:solnWeakAng}, where |
| 618 |
+ |
the effect of group-based cutoffs and switching functions on the {\sc |
| 619 |
+ |
sp} and {\sc sf} potentials are investigated. |
| 620 |
+ |
|
| 621 |
|
\begin{table}[htbp] |
| 622 |
|
\centering |
| 623 |
< |
\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 $\varepsilon \approx \infty$).} |
| 623 |
> |
\caption{Regression results for the strong NaCl solution |
| 624 |
> |
system. Tabulated results include $\Delta E$ values (top set), force |
| 625 |
> |
vector magnitudes (middle set) and torque vector magnitudes (bottom |
| 626 |
> |
set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted Force, |
| 627 |
> |
GSC = Group Switched Cutoff, and RF = Reaction Field (where |
| 628 |
> |
$\varepsilon \approx \infty$).} |
| 629 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 630 |
|
\\ |
| 631 |
|
\toprule |
| 672 |
|
RF & & 0.949 & 0.939 & 0.988 & 0.988 & 0.992 & 0.993 \\ |
| 673 |
|
\bottomrule |
| 674 |
|
\end{tabular} |
| 675 |
< |
\label{tab:sol10Tab} |
| 675 |
> |
\label{tab:solnStr} |
| 676 |
|
\end{table} |
| 677 |
|
|
| 678 |
|
\begin{table}[htbp] |
| 708 |
|
& 0.3 & 1.752 & 1.454 & 1.451 & 23.587 & 14.390 & 14.245 \\ |
| 709 |
|
\bottomrule |
| 710 |
|
\end{tabular} |
| 711 |
< |
\label{tab:sol10TabAng} |
| 711 |
> |
\label{tab:solnStrAng} |
| 712 |
|
\end{table} |
| 713 |
|
|
| 714 |
< |
\section{\label{app-argon}Argon Sphere in Water} |
| 714 |
> |
The {\sc rf} method struggles with the jump in ionic strength. The |
| 715 |
> |
configuration energy difference degrade to unuseable levels while the |
| 716 |
> |
forces and torques degrade in a more modest fashion. The {\sc rf} |
| 717 |
> |
method was designed for homogeneous systems, and this restriction is |
| 718 |
> |
apparent in these results. |
| 719 |
|
|
| 720 |
+ |
The {\sc sp} and {\sc sf} methods require larger cutoffs to maintain |
| 721 |
+ |
their agreement with {\sc spme}. With these results, we still |
| 722 |
+ |
recommend no to moderate damping for the {\sc sf} method and moderate |
| 723 |
+ |
damping for the {\sc sp} method, both with cutoffs greater than 12 |
| 724 |
+ |
\AA. |
| 725 |
+ |
|
| 726 |
+ |
\section{\label{app:argon}Argon Sphere in Water} |
| 727 |
+ |
|
| 728 |
+ |
The final model system studied was 6 \AA\ sphere of Argon solvated by |
| 729 |
+ |
SPC/E water. The results for the energy gap comparisons and the force |
| 730 |
+ |
and torque vector magnitude comparisons are shown in table |
| 731 |
+ |
\ref{tab:solnWeak}. The force and torque vector directionality |
| 732 |
+ |
results are displayed separately in table \ref{tab:solnWeakAng}, where |
| 733 |
+ |
the effect of group-based cutoffs and switching functions on the {\sc |
| 734 |
+ |
sp} and {\sc sf} potentials are investigated. |
| 735 |
+ |
|
| 736 |
|
\begin{table}[htbp] |
| 737 |
|
\centering |
| 738 |
< |
\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 $\varepsilon \approx \infty$).} |
| 738 |
> |
\caption{Regression results for the 6 \AA\ argon sphere in liquid |
| 739 |
> |
water system. Tabulated results include $\Delta E$ values (top set), |
| 740 |
> |
force vector magnitudes (middle set) and torque vector magnitudes |
| 741 |
> |
(bottom set). PC = Pure Cutoff, SP = Shifted Potential, SF = Shifted |
| 742 |
> |
Force, GSC = Group Switched Cutoff, and RF = Reaction Field (where |
| 743 |
> |
$\varepsilon \approx \infty$).} |
| 744 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 745 |
|
\\ |
| 746 |
|
\toprule |
| 787 |
|
RF & & 0.993 & 0.988 & 0.997 & 0.995 & 0.999 & 0.998 \\ |
| 788 |
|
\bottomrule |
| 789 |
|
\end{tabular} |
| 790 |
< |
\label{tab:argonTab} |
| 790 |
> |
\label{tab:argon} |
| 791 |
|
\end{table} |
| 792 |
|
|
| 793 |
|
\begin{table}[htbp] |
| 794 |
|
\centering |
| 795 |
< |
\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.} |
| 795 |
> |
\caption{Variance results from Gaussian fits to angular |
| 796 |
> |
distributions of the force and torque vectors in the 6 \AA\ sphere of |
| 797 |
> |
argon in liquid water system. PC = Pure Cutoff, SP = Shifted |
| 798 |
> |
Potential, SF = Shifted Force, GSC = Group Switched Cutoff, RF = |
| 799 |
> |
Reaction Field (where $\varepsilon \approx \infty$), GSSP = Group |
| 800 |
> |
Switched Shifted Potential, and GSSF = Group Switched Shifted Force.} |
| 801 |
|
\begin{tabular}{@{} ccrrrrrr @{}} |
| 802 |
|
\\ |
| 803 |
|
\toprule |
| 828 |
|
& 0.3 & 0.814 & 0.825 & 0.816 & 8.325 & 8.447 & 8.132 \\ |
| 829 |
|
\bottomrule |
| 830 |
|
\end{tabular} |
| 831 |
< |
\label{tab:argonTabAng} |
| 831 |
> |
\label{tab:argonAng} |
| 832 |
|
\end{table} |
| 833 |
|
|
| 834 |
+ |
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. |
| 835 |
+ |
|
| 836 |
|
\newpage |
| 837 |
|
|
| 838 |
|
\bibliographystyle{jcp2} |
| 839 |
|
\bibliography{electrostaticMethods} |
| 840 |
|
|
| 841 |
< |
\end{document} |
| 841 |
> |
\end{document} |
