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MCCCS Towhee (Shah and Maginn 2004)

 

 

Overview
    This section covers the Shah and Maginn 2004 (Shah2004) force field as it is implemented into the towhee_ff_Shah2004 file in the ForceFields directory. This force field was designed for an ionic liquid of 1-n-butyl-3-methylimidazolium [bmim] hexafluorophosphate [PF6]. Note that this is a Lennard-Jones force field that uses the 'Lorentz-Berthelot' mixing rules. Any discrepencies (especially typos) from the published values are the sole responsibility of Marcus G. Martin, and I welcome feedback on how this implementation compares with other programs.
References for Shah and Maginn 2004 Typos and comments for Shah and Maginn 2004
  • Full Lennard-Jones interactions are used for 1-4 interactions, while the Coulombic 1-4 terms are scaled by 1/2 [personal communication between E.J. Maginn and M.G. Martin 04-21-2006]. This is with the execption of the ring dihedrals that are held rigid and so there is no reason to compute the 1-4 terms.
  • Note that the coordinates presented for the PF6 structure result in asymmetric bond lengths and bending angles. I have inlcluded that as an atom-specific implementation of PF6, and I have also included an option for symmetric PF6 using the bond length from Morrow and Maginn 2002.
  • Note that all of the rigid interactions in this molecule means you need to start the simulation using a template for both molecules. Coordinates suitable for a template are found in Table 1 of Shah and Maginn 2004.
Shah and Maginn 2004 in Towhee
    The official force field name for Shah and Maginn 2004 in Towhee is 'Shah2004'. Here is the list of atom names for use in the towhee_input file, along with a brief description. These names correspond to those used in Shah and Maginn 2004. I have also included an option for a symmetric PF6 using a perfect octahedral geometry and a P-F bond length taken from Morrow and Maginn 2002. Please note that the capitalization and spacing pattern is important and must be followed exactly as listed here.
    • 'N1' : Ring Nitrogen bonded to C2, C5, and C7 in bmim
    • 'C2' : Ring Carbon (and an implicit bonded hydrogen) bonded to N1 and N3 in bmim
    • 'N3' : Ring Nitrogen bonded to C2, C4, and C6 in bmim
    • 'C4' : Ring Carbon (and an implicit bonded hydrogen) bonded to N3 and C5 in bmim
    • 'C5' : Ring Carbon (and an implicit bonded hydrogen) bonded to N1 and C4 in bmim
    • 'C6' : methyl Carbon (and three implicit bonded hydrogens) bonded to N3 in bmim
    • 'C7' : methylene Carbon (and two implicit bonded hydrogens) bonded to N1 and C8 in bmim
    • 'C8' : methylene Carbon (and two implicit bonded hydrogens) bonded to C7 and C9 in bmim
    • 'C9' : methylene Carbon (and two implicit bonded hydrogens) bonded to C8 and C10 in bmim
    • 'C10' : methyl Carbon (and three implicit bonded hydrogens) bonded to C9 in bmim
    • 'P' : P in hexafluorophosphate
    • 'F' : generic F in hexafluorophosphate if you want to use the symmetric bond length and bending angle version of that molecule.
    • 'F1' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
    • 'F2' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
    • 'F3' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
    • 'F4' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
    • 'F5' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
    • 'F6' : specific F in hexafluorophosphate if you want to use the assymmetric bond length and bending angle version of that molecule.
Coulombic interactions
    This force field uses point charges and has been set up to assign the point charges using the bond increment method. The charges for bmim are assigned according to Table 2 of Shah and Maginn 2004.
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Send comments to: Marcus G. Martin
Last updated: April 27, 2006