MCCCS Towhee (TraPPE Explict Hydrogen)



    This section covers the TraPPE Explicit Hydrogen (TraPPE-EH) force field as it is implemented into the towhee_ff_TraPPE-EH file in the ForceFields directory. All of the Towhee atom types for the TraPPE Explicit Hydrogen force field are listed, along with a short description of their meanings. For more information about the TraPPE family of force fields see the Siepmann group web site. Note that TraPPE-EH is a Lennard-Jones (12-6) force field and can only be combined with other Lennard-Jones (12-6) force fields. It is particularily suitable for combination with the TraPPE United Atom 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 TraPPE-EH
    TraPPE-EH is still under development by the Siepmann group. The current implementation includes only a subset of the total published parameters. Here is the current list of references.
TraPPE-EH in Towhee
    The official force field name for TraPPE Explicit Hydrogen in Towhee is 'TraPPE-EH'. Here I list all of the TraPPE-EH 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.
      Carbon Dioxide
    • 'C_co2' : central carbon in carbon dioxide.
    • 'O_co2' : oxygen in carbon dioxide.
    • N2
    • 'N_n2' : nitrogen atom in N2.
    • 'COM_n2' : center of mass in N2. This molecule is treated as a three site model with both of the nitrogen atoms bonded to the center-of-mass.
Coulombic interactions
    TraPPE-EH uses atom-centered, and other interaction site centered, point charges to represent the electrostatic interactions. The 'bond increment' method for assigning charges is implemented for these molecules. Please see the inpstyle 2 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.
    • O_co2 - O_co2: -0.35
    • N_n2 - COM_n2: -0.482
Improper torsions
    TraPPE-EH does not utilize improper torsions.
Return to the Towhee Capabilities web page


Send comments to: Marcus G. Martin
Last updated: September 07, 2005