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<title>MCCCS Towhee (Walt2001)</title>
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<div align="center"> <font size="5"> <b><font face="Arial, Helvetica, sans-serif"><a name="top"></a>MCCCS
Towhee (Walther <i>et al.</i> 2001)</font></b> </font> </div>
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<td width="697" valign="top"> <b>Overview</b>
<ul>
This section covers the Walther <i>et al.</i> (Walt2001) force field as it is implemented into
the towhee_ff_Walt2001 file in the ForceFields directory. This force field was originally
designed for fluid simulations of water and carbon nanotubes.
Note that this is a Lennard-Jones force field that uses explicit mixing rules so it is
not easily combined with other force fields.
Any discrepencies (especially typos) from the published 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 Walt2001</b>
<ul>
What I term Walt2001 is described in the following paper.
<ul>
<li><a href="../references.html#walther_et_al_2001">Walther <i>et al.</i> 2001</a></li>
</ul>
</ul>
<b>Typos and comments for Walt2001</b>
<ul>
There are some typos in the Walt2001 paper. Here I list places where my implementation does
not completely agree with what is written in the Walt2001 paper.
<ul>
<li>Table 1 of <a href="../references.html#walther_et_al_2001">Walther <i>et al.</i> 2001</a>
lists no values for the angle force constant and two for the torsional force constant.
This implementation assumes that the second of these values (25.12 kJ mol<sup>-1</sup>) is
the torsional force constant, while the first value (562.2 kJ mol<sup>-1</sup>) is
the angle force constant.
</li>
<li>Table 2 of <a href="../references.html#walther_et_al_2001">Walther <i>et al.</i> 2001</a>
lists a charge of -0.41 e for the hydrogen atom in water. This implemenation assumes they
really meant a charge of +0.41 e for the hydrogen atom in water.
</li>
</ul>
</ul>
<b>Walt2001 in Towhee</b>
<ul>
The official force field name for Walther <i>et al.</i> 2001 in Towhee is 'Walt2001'. Here I list all of
the 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>
<li><b>'C'</b> : Carbon in a carbon nanotube.</li>
<li><b>'O'</b> : Oxygen in water.</li>
<li><b>'H'</b> : Hydrogen in water.</li>
</ul>
</ul>
<b>Coulombic interactions</b>
<ul>
This force field assigns coulombic interactions to the water molecules. In the original paper
they also used quadrupole moments on the carbon atoms, but they found these had no significant
effect on the results and so the quadrupole moment is not included in this implementation.
The 'bond increment' method of <b>charge_assignment</b> is implemented for this forcefield.
Please see the <a href="../inpstyle/inpstyle_2.html">inpstyle 2</a> documentation for
further information on enabling this option. Otherwise, you are welcome to manually set the charges. Here I
list the charges transfered between atom pairs as assigned by the 'bond increment' method.
<ul>
<li><font color="green">O</font> - <font color="green">H</font>: -0.41</li>
<li><font color="green">C</font> - <font color="green">C</font>: 0.0</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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