MCCCS Towhee (Fris2003)



    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.


References for Frischknecht and Curro (Fris2003)
    This force field is a hybrid of an earlier version of the Compass force field and a united-atom forcefield of Sok et al.. Please see the following reference for more details. 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 deg2). They are actually listed in the more typical kcal/(mol rad2) (personal communication between M.G. Martin and A.L. Frischknecht October 2003).
Frischknecht and Curro in Towhee
    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.
    • 'CH3' : united-atom methyl group (one carbon and 3 hydrogens)
    • 'O' : oxygen
    • 'Si' : silicon
Coulombic Interactions
    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.
Improper torsions
    There are no improper torsions for this force field.
    This force field does not have parameters for proteins.
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Send comments to: Marcus G. Martin
Last updated: September 07, 2005