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<div align="center"> <font size="5"> <b><font face="Arial, Helvetica, sans-serif"><a name="top"></a>MCCCS
Towhee (Fris2003)</font></b> </font> </div>
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<p> </p>
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<td width="697" valign="top"> <b>Overview</b>
<ul>
This section covers the Frischknecht and Curro United-Atom
force field for poly(dimethylsiloxane) as it is implemented in
the towhee_ff_Fris2003 file in the ForceFields directory. All
of the Towhee atom types for this force field are listed,
along with a short description of their meanings. Note that
this force field is a hybrid of Lennard-Jones (12-6) and
Lennard-Jones (9-6) which ends up being a 12-9-6 potential and
their implementation does not have general mixing rules for
combination with other potentials. I would like to
acknowledge Amalie L. Frischknecht for providing very useful
guidance about implementing this 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. <p> </p>
</ul>
<b>References for Frischknecht and Curro (Fris2003)</b>
<ul>
This force field is a hybrid of an earlier version of the Compass force field and a united-atom forcefield
of Sok <i>et al.</i>. Please see the following reference for more details.
<ul>
<li><a href="../references.html#frischknecht_curro_2003">Frischknecht and Curro 2003</a></li>
</ul>
with the exception that there is a typo in Table 1 of that paper which states the units for the angle force constant
are kcal/(mol deg<sup>2</sup>). They are actually listed in the more typical kcal/(mol rad<sup>2</sup>) (personal
communication between M.G. Martin and A.L. Frischknecht October 2003).
</ul>
<b>Frischknecht and Curro in Towhee</b>
<ul>
The official force field name for these parameters is 'Fris2003' (starting with version 3.13.0) Here I list all of the
atom names for use in the towhee_input file, along with a brief description of what atoms we are talking about.
Please note that the capitalization and spacing pattern is important
and must be followed exactly as listed here.
<ul>
<li><b>'CH3'</b> : united-atom methyl group (one carbon and 3 hydrogens)</li>
<li><b>'O'</b> : oxygen</li>
<li><b>'Si'</b> : silicon</li>
</ul>
</ul>
<b>Coulombic Interactions</b>
<ul>
This force field uses point charges on atomic centers. They offer several possible charge sets in their paper,
but it looks like they recomend two possible models. In the first, the charge is set to 0.0 on every atom (that is,
there are no coulombic interactions). In the second, the charge is still 0.0 on the methyl groups, Si has a 0.3 charge,
and O has a -0.3 charge.
</ul>
<b>Improper torsions</b>
<ul>
There are no improper torsions for this force field.
</ul>
<b>Proteins</b>
<ul>
This force field does not have parameters for proteins.
</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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