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\documentclass[aps,jcp,preprint,showpacs,superscriptaddress,groupedaddress]{revtex4-1} |
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\begin{document} |
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|
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\title{Supporting Information for: Interfacial Thermal Conductance of Thiolate-Protected |
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Gold Nanospheres} |
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\author{Kelsey M. Stocker} |
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\author{Suzanne M. Neidhart} |
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\author{J. Daniel Gezelter} |
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\email{gezelter@nd.edu} |
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\affiliation{Department of Chemistry and Biochemistry, University of |
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Notre Dame, Notre Dame, IN 46556} |
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\date{\today} |
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|
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\begin{abstract} |
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This document supplies force field parameters for the united-atom |
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sites, bond, bend, and torsion parameters, as well as the cross |
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interactions between the united-atom sites and the gold atoms. These |
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parameters were used in the simulations presented in the main text. |
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\end{abstract} |
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|
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|
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\maketitle |
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|
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Gold -- gold interactions were described by the quantum Sutton-Chen |
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(QSC) model.\cite{Qi:1999ph} The hexane solvent is described by the |
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TraPPE united atom model,\cite{TraPPE-UA.alkanes} where sites are |
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located at the carbon centers for alkyl groups. Bonding interactions |
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were used for intra-molecular sites closer than 3 bonds. Effective |
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Lennard-Jones potentials were used for non-bonded interactions. |
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|
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\begin{table}[h] |
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\bibpunct{}{}{,}{n}{}{,} |
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\centering |
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\caption{Non-bonded interaction parameters (including cross interactions with Au atoms). \label{tab:atypes}} |
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\begin{tabular}{ c|cccccl } |
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\toprule |
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Site & mass & $\sigma_{ii}$ & $\epsilon_{ii}$ & $\sigma_{\ce{Au}-i}$ & $\epsilon_{\ce{Au}-i}$ & source \\ |
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& (amu)& (\AA) & (kcal/mol) & (\AA) & (kcal/mol) & \\ |
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\colrule |
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\ce{CH3} & 15.04 & 3.75 & 0.1947 & 3.54 & 0.2146 & Refs. \protect\cite{TraPPE-UA.alkanes}, \protect\cite{vlugt:cpc2007154} and \protect\cite{landman:1998}\\ |
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\ce{CH2} & 14.03 & 3.95 & 0.09141& 3.54 & 0.1749 & Refs. \protect\cite{TraPPE-UA.alkanes}, \protect\cite{vlugt:cpc2007154} and \protect\cite{landman:1998}\\ |
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CHene & 13.02 & 3.73 & 0.09340& 3.4625 & 0.1680 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes}, \protect\cite{vlugt:cpc2007154} and \protect\cite{landman:1998}\\ |
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S & 32.0655 & 4.45 & 0.2504 & 2.40 & 8.465 & Refs. \protect\cite{landman:1998} ($\sigma$) and \protect\cite{vlugt:cpc2007154} ($\epsilon$) \\ |
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CHar & 13.02 & 3.695 & 0.1004 & 3.4625 & 0.1680 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{vlugt:cpc2007154}\\ |
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\ce{CH2ar} & 14.03 & 3.695 & 0.1004 & 3.4625 & 0.1680 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{vlugt:cpc2007154}\\ |
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\botrule |
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\end{tabular} |
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\bibpunct{[}{]}{,}{n}{,}{,} |
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\end{table} |
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|
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The TraPPE-UA force field includes parameters for thiol |
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molecules\cite{TraPPE-UA.thiols} which were used for the |
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alkanethiolate molecules in our simulations. To derive suitable |
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parameters for butanethiolate adsorbed on Au(111) surfaces, we adopted |
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the S parameters from Luedtke and Landman\cite{landman:1998} and |
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modified the parameters for the CTS atom to maintain charge neutrality |
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in the molecule. |
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|
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Bonds are typically rigid in TraPPE-UA, so although we used |
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equilibrium bond distances from TraPPE-UA, for flexible bonds, we |
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adapted bond stretching spring constants from the OPLS-AA force |
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field.\cite{Jorgensen:1996sf} |
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|
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\begin{table}[h] |
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\bibpunct{}{}{,}{n}{}{,} |
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\centering |
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\caption{Bond parameters. \label{tab:bond}} |
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\begin{tabular}{ cc|ccl } |
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\toprule |
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$i$&$j$ & $r_0$ & $k_\mathrm{bond}$ & source \\ |
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& & (\AA) & $(\mathrm{~kcal/mole/\AA}^2)$ & \\ |
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\colrule |
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\ce{CH3} & \ce{CH3} & 1.540 & 536 & Refs. \protect\cite{TraPPE-UA.alkanes} and \protect\cite{Jorgensen:1996sf}\\ |
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\ce{CH3} & \ce{CH2} & 1.540 & 536 & Refs. \protect\cite{TraPPE-UA.alkanes} and \protect\cite{Jorgensen:1996sf} \\ |
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\ce{CH2} & \ce{CH2} & 1.540 & 536 & Refs. \protect\cite{TraPPE-UA.alkanes} and \protect\cite{Jorgensen:1996sf} \\ |
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CHene & CHene & 1.330 & 1098 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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\ce{CH3} & CHene & 1.540 & 634 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf} \\ |
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\ce{CH2} & CHene & 1.540 & 634 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf} \\ |
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S & \ce{CH2} & 1.820 & 444 & Refs. \protect\cite{TraPPE-UA.thiols} and \protect\cite{Jorgensen:1996sf} \\ |
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CHar & CHar & 1.40 & 938 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf} \\ |
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CHar & \ce{CH2} & 1.540 & 536 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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CHar & \ce{CH3} & 1.540 & 536 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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\ce{CH2ar} & CHar & 1.40 & 938 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf} \\ |
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S & CHar & 1.80384 & 527.951 & This Work \\ |
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\botrule |
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\end{tabular} |
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\bibpunct{[}{]}{,}{n}{,}{,} |
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\end{table} |
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|
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To describe the interactions between metal (Au) and non-metal atoms, |
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potential energy terms were adapted from an adsorption study of alkyl |
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thiols on gold surfaces by Vlugt, \textit{et |
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al.}\cite{vlugt:cpc2007154} They fit an effective pair-wise |
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Lennard-Jones form of potential parameters for the interaction between |
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Au and pseudo-atoms CH$_x$ and S based on a well-established and |
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widely-used effective potential of Hautman and Klein for the Au(111) |
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surface.\cite{hautman:4994} |
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|
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Parameters not found in the TraPPE-UA force field for the |
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intramolecular interactions of the conjugated and the penultimate |
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alkenethiolate ligands were calculated using constrained geometry |
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scans using the B3LYP functional~\cite{Becke:1993kq,Lee:1988qf} and |
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the 6-31G(d,p) basis set. Structures were scanned starting at the |
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minimum energy gas phase structure for small ($C_4$) ligands. Only |
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one degree of freedom was constrained for any given scan -- all other |
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atoms were allowed to minimize subject to that constraint. The |
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resulting potential energy surfaces were fit to a harmonic potential |
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for the bond stretching, |
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\begin{equation} |
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V_\mathrm{bond} = \frac{k_\mathrm{bond}}{2} \left( r - r_0 \right)^2, |
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\end{equation} |
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and angle bending potentials, |
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\begin{equation} |
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V_\mathrm{bend} = \frac{k_\mathrm{bend}}{2} \left(\theta - \theta_0\right)^2. |
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\end{equation} |
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Torsional potentials were fit to the TraPPE torsional function, |
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\begin{equation} |
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V_\mathrm{tor} = c_0 + c_1 \left(1 + \cos\phi \right) + c_2 \left(1 - \cos 2\phi \right) + c_3 \left(1 + \cos 3 \phi \right). |
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\end{equation} |
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|
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For the penultimate thiolate ligands, the model molecule used was |
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2-Butene-1-thiol, for which one bend angle (\ce{S-CH2-CHene}) was |
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scanned to fit an equilibrium angle and force constant, as well as one |
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torsion (\ce{S-CH2-CHene-CHene}). The parameters for these two |
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potentials also served as model for the longer conjugated thiolate |
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ligands which require bend angle parameters for (\ce{S-CH2-CHar}) and |
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torsion parameters for (\ce{S-CH2-CHar-CHar}). |
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|
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For the $C_4$ conjugated thiolate ligands, the model molecule for the |
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quantum mechanical calculations was 1,3-Butadiene-1-thiol. This |
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ligand required fitting one bond (\ce{S-CHar}), and one bend angle |
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(\ce{S-CHar-CHar}). |
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|
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The geometries of the model molecules were optimized prior to |
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performing the constrained angle scans, and the fit values for the |
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bond, bend, and torsional parameters were in relatively good agreement |
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with similar parameters already present in TraPPE. |
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|
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|
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\begin{table}[h] |
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\bibpunct{}{}{,}{n}{,}{,} |
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\centering |
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\caption{Bend angle parameters. The central atom in the bend is atom $j$.\label{tab:bend}} |
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\begin{tabular}{ ccc|ccl } |
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\toprule |
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$i$&$j$&$k$ & $\theta_0$ & $k_\mathrm{bend}$ & source\\ |
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& & & ($\degree$) & (kcal/mol/rad\textsuperscript{2}) & \\ |
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\colrule |
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\ce{CH2} & \ce{CH2} & S & 114.0 & 124.20& Ref. \protect\cite{TraPPE-UA.thiols}\\ |
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\ce{CH3} & \ce{CH2} & \ce{CH2} & 114.0 & 124.20& Ref. \protect\cite{TraPPE-UA.thiols}\\ |
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\ce{CH2} & \ce{CH2} & \ce{CH2} & 114.0 & 124.20& Ref. \protect\cite{TraPPE-UA.thiols}\\ |
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CHene & CHene & \ce{CH3} & 119.7 & 139.94& Ref. \protect\cite{TraPPE-UA.alkylbenzenes}\\ |
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CHene & CHene & \ce{CH2} & 119.7 & 139.94& Ref. \protect\cite{TraPPE-UA.alkylbenzenes}\\ |
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\ce{CH2} & \ce{CH2} & CHene & 114.0 & 124.20& Ref. \protect\cite{TraPPE-UA.alkylbenzenes}\\ |
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CHar & CHar & CHar & 120.0 & 126.0 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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CHar & CHar & \ce{CH2} & 120.0 & 140.0 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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CHar & CHar & \ce{CH3} & 120.0 & 140.0 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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CHar & CHar & \ce{CH2ar}& 120.0 & 126.0 & Refs. \protect\cite{TraPPE-UA.alkylbenzenes} and \protect\cite{Jorgensen:1996sf}\\ |
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S & \ce{CH2} & CHene & 109.97 & 127.37 & This work \\ |
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S & \ce{CH2} & CHar & 109.97 & 127.37 & This work \\ |
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S & CHar & CHar & 123.911 & 138.093 & This work \\ |
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\botrule |
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\end{tabular} |
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\bibpunct{[}{]}{,}{n}{,}{,} |
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\end{table} |
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|
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\begin{table}[h] |
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\bibpunct{}{}{,}{n}{,}{,} |
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\centering |
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\caption{Torsion parameters. The central atoms for each torsion are atoms $j$ and $k$, |
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and wildcard atom types are denoted by ``X''. All $c_n$ parameters |
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have units of kcal/mol. The torsions around carbon-carbon double bonds |
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are harmonic and assume a trans (180$\degree$) geometry. The force |
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constant for this torsion is given in $\mathrm{kcal~mol~}^{-1}\mathrm{degrees}^{-2}$. \label{tab:torsion}} |
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\begin{tabular}{ cccc|ccccl } |
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\toprule |
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$i$&$j$&$k$&$l$& $c_0$&$c_1$& $c_2$ & $c_3$ & source\\ |
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\colrule |
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\ce{CH3} & \ce{CH2} & \ce{CH2} & \ce{CH2} & 0.0 & 0.7055 & -0.13551 & 1.5725 & Ref. \protect\cite{TraPPE-UA.alkanes}\\ |
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\ce{CH2} & \ce{CH2} & \ce{CH2} & \ce{CH2} & 0.0 & 0.7055 & -0.13551 & 1.5725 & Ref. \protect\cite{TraPPE-UA.alkanes}\\ |
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\ce{CH2} & \ce{CH2} & \ce{CH2} & S & 0.0 & 0.7055 & -0.13551 & 1.5725 & Ref. \protect\cite{TraPPE-UA.thiols}\\ \colrule |
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X & CHene & CHene & X & \multicolumn{4}{c}{\multirow{2}{*}{$V = \frac{0.008112}{2} (\phi - 180.0)^2$}} & \multirow{2}{*}{Ref. \protect\cite{TraPPE-UA.alkylbenzenes}} \\ |
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X & CHar & CHar & X & & & & & \\ \colrule |
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\ce{CH2} & \ce{CH2} & CHene & CHene & 1.368 & 0.1716 & -0.2181 & -0.56081 & Ref. \protect\cite{TraPPE-UA.alkylbenzenes}\\ |
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\ce{CH2} & \ce{CH2} & \ce{CH2} & CHene & 0.0 & 0.7055 & -0.13551 & 1.5725 & Ref. \protect\cite{TraPPE-UA.alkylbenzenes}\\ |
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CHene & CHene & \ce{CH2} & S & 3.20753 & 0.207417 & -0.912929& -0.958538 & This work \\ |
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CHar & CHar & \ce{CH2} & S & 3.20753 & 0.207417 & -0.912929& -0.958538 & This work \\ |
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\botrule |
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\end{tabular} |
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\bibpunct{[}{]}{,}{n}{,}{,} |
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\end{table} |
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|
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\newpage |
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\bibliographystyle{aip} |
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\bibliography{NPthiols} |
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\end{document} |
