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<title>MCCCS Towhee (TraPPE Explicit Hydrogen)</title>
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<div align="center"> <font size="5"> <b><font face="Arial, Helvetica, sans-serif"><a name="top"></a>MCCCS
Towhee (TraPPE Explict Hydrogen)</font></b> </font> </div>
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<td width="697" valign="top"> <b>Overview</b>
<ul>
This section covers the TraPPE Explicit Hydrogen (TraPPE-EH) force field as it is implemented into
the towhee_ff_TraPPE-EH file in the ForceFields directory. All of the Towhee atom types for the TraPPE
Explicit Hydrogen force field are listed, along with a short description of their meanings. For
more information about the TraPPE family of force fields see the
<a href="http://siepmann6.chem.umn.edu/">Siepmann group web site</a>.
Note that TraPPE-EH is a Lennard-Jones (12-6) force field and can only be combined with
other Lennard-Jones (12-6) force fields. It is particularily suitable for combination with
the <a href="trappeua.html">TraPPE United Atom</a> force field.
Any discrepencies (especially typos) from the published force field values are the sole
responsibility of Marcus G. Martin, and I welcome feedback on how this
implementation compares with other programs.
</ul>
<b>References for TraPPE-EH</b>
<ul>
TraPPE-EH is still under development by the Siepmann group. The current implementation includes
only a subset of the total published parameters. Here is the current list of references.
<ul>
<li><a href="../references.html#potoff_siepmann_2001">Potoff and Siepmann 2001</a></li>
</ul>
</ul>
<b>TraPPE-EH in Towhee</b>
<ul>
The official force field name for TraPPE Explicit Hydrogen in Towhee is 'TraPPE-EH'. Here I list all of
the TraPPE-EH atom names for use in the towhee_input file, along with a brief description. I created these
atom names in order to work with the molecule assembler.
Please note that the capitalization and spacing pattern is important
and must be followed exactly as listed here.
<ul>
<dt><font color="red">Carbon Dioxide</font></dt>
<li><b>'C_co2'</b> : central carbon in carbon dioxide.</li>
<li><b>'O_co2'</b> : oxygen in carbon dioxide.</li>
<dt><font color="red">N<sub>2</sub></font></dt>
<li><b>'N_n2'</b> : nitrogen atom in N<sub>2</sub>.</li>
<li><b>'COM_n2'</b> : center of mass in N<sub>2</sub>. This molecule is treated as a three site
model with both of the nitrogen atoms bonded to the center-of-mass.</li>
</ul>
</ul>
<b>Coulombic interactions</b>
<ul>
TraPPE-EH uses atom-centered, and other interaction site centered, point charges to represent the
electrostatic interactions.
The 'bond increment' method for assigning charges is implemented for these molecules.
Please see the <a href="../inpstyle/inpstyle_2.html">inpstyle 2</a> documentation for
further information on enabling this option.
Here I list the bond increments for the atom names listed above. The value of the bond increment is added
to the first atom listed and subtracted from the second atom listed.
<ul>
<li><font color="green">O_co2</font> - <font color="green">O_co2</font>: -0.35</li>
<li><font color="green">N_n2</font> - <font color="green">COM_n2</font>: -0.482</li>
</ul>
</ul>
<b>Improper torsions</b>
<ul>
TraPPE-EH does not utilize improper torsions.
</ul>
<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 -->September 07, 2005<!-- #EndDate -->
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