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MCCCS Towhee (Elementary Physical Models)

 

 

Overview
    This section covers three Elementary Physical Models (EPM) for CO2 as they are implemented into the towhee_ff_EPM file in the ForceFields directory. All of the Towhee atom types for these EPM force fields are listed, along with a short description of their meanings. Note that EPM are Lennard-Jones (12-6) force fields that use Geometric mixing rules and can only be combined with other Lennard-Jones (12-6) force fields. 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 EPM EPM in Towhee
    The official force field name for the Elementary Physical Models in Towhee is 'EPM'. Here I list all of the EPM 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. There are three different variants of the carbon dioxide potentials present in this force field and all are implemented here. Please note that the capitalization and spacing pattern is important and must be followed exactly as listed here.
      EPM Rigid Carbon Dioxide
        This model is taken from the first part of Table 1 in Harris and Yung 1995. It has a rigid bending angle for CO2
    • 'C_EPM-R' : central carbon in carbon dioxide.
    • 'O_EPM-R' : oxygen in carbon dioxide.
    EPM Flexible Carbon Dioxide
      This model is taken from the first part of Table 1 in Harris and Yung 1995. It has a flexible bending angle for CO2
  • 'C_EPM-F' : central carbon in carbon dioxide.
  • 'O_EPM-F' : oxygen in carbon dioxide.
EPM2 Carbon Dioxide
    This model is taken from the second part of Table 1 in Harris and Yung 1995. It has a flexible bending angle for CO2
  • 'C_EPM2' : central carbon in carbon dioxide.
  • 'O_EPM2' : oxygen in carbon dioxide.
  • Coulombic interactions
      EPM uses atom-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.
      • C_EPM-R - O_EPM-R: 0.33225
      • C_EPM-F - O_EPM-F: 0.33225
      • C_EPM2 - O_EPM2: 0.3256
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    Send comments to: Marcus G. Martin
    Last updated: September 07, 2005