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.
- '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.
TraPPE-EH uses atom-centered, and other interaction site centered, point charges to represent the
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
TraPPE-EH does not utilize improper torsions.
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