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<title>MCCCS Towhee (Elementary Physical Models)</title>
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<div align="center"> <font size="5"> <b><font face="Arial, Helvetica, sans-serif"><a name="top"></a>MCCCS
Towhee (Elementary Physical Models)</font></b> </font> </div>
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<td width="697" valign="top"> <b>Overview</b>
<ul>
This section covers three Elementary Physical Models (EPM) for CO<sub>2</sub> as they are implemented into
the towhee_ff_EPM file in the ForceFields directory. All of the Towhee atom types for these EPM
force fields are listed, along with a short description of their meanings.
Note that EPM are Lennard-Jones (12-6) force fields that use Geometric mixing rules and can only
be combined with other Lennard-Jones (12-6) force fields.
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 EPM</b>
<ul>
The three EPM models are presented in a single paper by Harris and Yung.
<ul>
<li><a href="../references.html#harris_yung_1995">Harris and Yung 1995</a></li>
</ul>
</ul>
<b>EPM in Towhee</b>
<ul>
The official force field name for the Elementary Physical Models in Towhee is 'EPM'. Here I list all of
the EPM 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. There are three different variants of the
carbon dioxide potentials present in this force field and all are implemented here.
Please note that the capitalization and spacing pattern is important
and must be followed exactly as listed here.
<ul>
<dt><font color="red">EPM Rigid Carbon Dioxide</font><dt>
<ul>This model is taken from the first part of Table 1 in
<a href="../references.html#harris_yung_1995">Harris and Yung 1995</a>.
It has a rigid bending angle for CO<sub>2</sub></dt>
<li><b>'C_EPM-R'</b> : central carbon in carbon dioxide.</li>
<li><b>'O_EPM-R'</b> : oxygen in carbon dioxide.</li>
</ul>
<dt><font color="red">EPM Flexible Carbon Dioxide</font><dt>
<ul>This model is taken from the first part of Table 1 in
<a href="../references.html#harris_yung_1995">Harris and Yung 1995</a>.
It has a flexible bending angle for CO<sub>2</sub></dt>
<li><b>'C_EPM-F'</b> : central carbon in carbon dioxide.</li>
<li><b>'O_EPM-F'</b> : oxygen in carbon dioxide.</li>
</ul>
<dt><font color="red">EPM2 Carbon Dioxide</font><dt>
<ul>This model is taken from the second part of Table 1 in
<a href="../references.html#harris_yung_1995">Harris and Yung 1995</a>.
It has a flexible bending angle for CO<sub>2</sub></dt>
<li><b>'C_EPM2'</b> : central carbon in carbon dioxide.</li>
<li><b>'O_EPM2'</b> : oxygen in carbon dioxide.</li>
</ul>
</ul>
</ul>
<b>Coulombic interactions</b>
<ul>
EPM uses atom-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">C_EPM-R</font> - <font color="green">O_EPM-R</font>: 0.33225</li>
<li><font color="green">C_EPM-F</font> - <font color="green">O_EPM-F</font>: 0.33225</li>
<li><font color="green">C_EPM2</font> - <font color="green">O_EPM2</font>: 0.3256</li>
</ul>
</ul>
<a href="../towhee_capabilities.html">Return to the Towhee Capabilities web page</a>
<p> </p>
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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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