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MCCCS Towhee (TraPPE United Atom Flexible Bonds)

 

 

Overview
    This section covers the TraPPE United Atom Flexible Bonds (TraPPE-UAf) force field as it is implemented into the towhee_ff_TraPPE-UAf 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. For more information about the TraPPE force fields see the Siepmann group web site. Note that TraPPE United Atom Flexible bonds is a Lennard-Jones (12-6) force field and can only be combined with other Lennard-Jones (12-6) force fields. This forcefield is a subset of the rigid bond TraPPE-UA force field with the change that the bond lengths are no longer rigid and are instead flexible using parameters from some other papers. Any discrepencies (especially typos) from the published TraPPE-UA force field values had better not exist considering I helped create this force field. If someone does find a discrepancy with the published values I would be extremely grateful if they let me know about it. I welcome feedback on how this implementation compares with other programs.
References for TraPPE-UAf Typos and comments for TraPPE-UAf
    Please see the closely related TraPPE-UA force field for typos and comments about this force field.
TraPPE-UAf in Towhee
    The official force field name for TraPPE United Atom Flexible Bonds in Towhee is 'TraPPE-UAf'. Here I list all of the TraPPE-UAf atom names for use in the towhee_input file, along with a brief description. These atom name are the same as those in the rigid bond TraPPE-UA force field and have the same meanings. Please note that the capitalization and spacing pattern is important and must be followed exactly as listed here.
      Carbon (not bonded to any hydrogens)
    • 'Ccccc(sp3)' : an sp3 carbon. This atom is single bonded to four carbon atoms. Bond name Csp3.
    • Carbon (united atom including 1 bonded hydrogen)
    • 'CHccc(sp3)' : united-atom consisting of an sp3 carbon and one bonded hydrogen. This united-atom is single bonded to three carbon atoms. Bond name Csp3.
    • Carbon (united atom including 2 bonded hydrogens)
    • 'CH2**(sp3)' : united-atom consisting of an sp3 carbon and two bonded hydrogens. This united-atom is single bonded to any two non-hydrogen atoms. Bond name Csp3.
    • Carbon (united atom including 3 bonded hydrogens)
    • 'CH3*(sp3)' : united-atom consisting of an sp3 carbon and three bonded hydrogens. This united-atom is single bonded to any non-hydrogen atom. Bond name Csp3.
    • Carbon (united atom including 4 bonded hydrogens)
    • 'CH4' : methane
Coulombic interactions
    TraPPE-UA uses atom-centered point charges to represent the electrostatic interactions. There are no coulombic interactions for the atom types currently implemented in this force field. Here I list the bond increments using the bond names listed above. The value of the bond increment is added to the first atom listed and subtracted from the second atom listed.
    • Csp3 - Csp3: 0.0
Improper torsions
    TraPPE-UAf does not utilize improper torsions.
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Send comments to: Marcus G. Martin
Last updated: November 12, 2005