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<title>MCCCS Towhee (Charmm27x)</title>
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<div align="center"> <font size="5"> <b><font face="Arial, Helvetica, sans-serif"><a name="top"></a>MCCCS
Towhee (Charmm22 Extra Parameters for Fluoroalkanes)</font></b> </font> </div>
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<p> </p>
<p> </p>
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<td width="697" valign="top"> <b>Overview</b>
<ul>
This section covers some extra parameters for use in combination with the
<a href="charmm22.html">CHARMM22</a> force field as it is implemented into the
towhee_ff_Charmm22fe file in the ForceFields directory.
This file is only likely to be useful in combination with the standard CHARMM22 forcefield.
Charmm22x is a Lennard-Jones (12-6) force field and typically uses
the Lorentz-Berthelot mixing rules. The parameters in this force field were developed for fluoroethanes. However,
to extend the force field's capability to handle other fluorohydrocarbons, missing bond, angle and torsion terms are assumed to
be equal to the similar ones reported in the reference. These new additions are the sole responsibility of Marcus G. Martin.
<p> </p>
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<b>References for Charmm22fe</b>
<ul>
The references for these additional parameters
<li><a href="../references.html#Chen_2001">Chen et. al 2001</a></li>
and <a href="http://www.pharmacy.umaryland.edu/faculty/amackere/force_fields.htm">MacKerell force fields site.</a>
</ul>
<b>Charmm22fe in Towhee</b>
<ul>
The official force field name for Charmm222fe in Towhee is 'Charmm22' as the name has to be the same in order to get the
molecule assembler to consider these parameters when building a molecule. Here is the list
of atom names for use in the towhee_input file, along with a brief description.
Please note that the capitalization and spacing pattern is important
and must be followed exactly as listed here.
<ul>
<li><b>'CF1'</b> : carbon in monofluoroethane</li>
<li><b>'CF2'</b> : carbon in difluoroethane</li>
<li><b>'CF3'</b> : carbon in trifluoroethane</li>
<li><b>'HF1'</b> : hydrogen in monofluoroethanes</li>
<li><b>'HF2'</b> : hydrogen in difluoroethanes</li>
<li><b>'F1'</b> : fluorine in monofluoroethane</li>
<li><b>'F2'</b> : fluorine in difluoroethane</li>
<li><b>'F3'</b> fluorine in trifluoroethane</li>
</ul>
</ul>
<b>Coulombic interactions</b>
<ul>
In the original paper following partial charges were reported
<li><b>'CF1'</b> -0.06</li>
<li><b>'CF2'</b> 0.24</li>
<li><b>'CF3'</b> 0.38</li>
<li><b>'HF1'</b> 0.11</li>
<li><b>'HF2'</b> 0.10</li>
<li><b>'F1'</b> -0.22</li>
<li><b>'F2'</b> -0.19</li>
<li><b>'F3'</b> -0.15</li>
</ul>
<p> </p>
<a href="../towhee_capabilities.html">Return to the Towhee Capabilities web page</a>
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<i><font size="2">Send comments to:</font></i> <font size="2">
<a href="mailto:marcus_martin@users.sourceforge.net">Marcus G. Martin</a><br>
<i>Last updated:</i>
<!-- #BeginDate format:Am1 -->May 03, 2006<!-- #EndDate -->
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