This section covers the Charmm27 Rigid Water force field as it is implemented into the
towhee_ff_C27rigid 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.
This is a Lennard-Jones (12-6) force field and typically uses
the Lorentz-Berthelot mixing rules. It uses the same parameters as the regular
Charmm27 force field, with the notable exception that all
of the intramolecular terms are rigid. 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 Charmm27 Rigid Water
The best literature references for the Charmm27 forcefield parameters are
More information about the Charmm27 forcefield is available on the Towhee
Charmm27 web manual page. C27rigid is simply a rigid implementation
of the Charmm27 water model where the equilibrium values of the bond and angle are set to be rigid
instead of flexible. This force field was implemented to allow comparison with simulations using the
standard molecular dynamics practice of freezing out intramolecular motion in water in order to speed
C27rigid in Towhee
The official force field name for Charmm27 Rigid Water in Towhee is 'C27rigid'. Here I list all
of the atom names for use in the towhee_input file, along with a brief
Please note that the capitalization and spacing pattern is important
and must be followed exactly as listed here.
- 'HT' : Water hydrogen, modified TIP3P model
- 'OT' : Water oxygen, modified TIP3P model
Charmm27 Rigid Water utilizes point charges on atomic centers to represent the charge distribution on a molecule.
The 'bond increment' method for assigning charges is implemented for this force field.
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.
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