Overview
This section covers the Walther et al. (Walt2001) force field as it is implemented into the towhee_ff_Walt2001 file in the ForceFields directory.
This force field was originally designed for fluid simulations of water and carbon nanotubes.
Note that this is a Lennard-Jones force field that uses explicit mixing rules so it is not easily combined with other force fields.
Any discrepencies (especially typos) from the published values are the sole responsibility of Marcus Martin,
and I welcome feedback on how this implementation compares with other programs.
References for Walt2001
The Walt2001 forcefield is described in the following paper.
Typos and comments for Walt2001
This section contains a list of places where the Towhee implementation of Walt2001 differs from the text of the Walt2001 paper.
- Table 1 of Walther et al. 2001 lists no values for the angle force constant
and two for the torsional force constant.
The Towhee implementation assumes that the second of these values (25.12 kJ mol-1) is the torsional force constant,
while the first value (562.2 kJ mol-1) is the angle force constant.
- Table 2 of Walther et al. 2001 lists a charge of -0.41 e for the hydrogen atom in water.
This implementation assumes they meant a charge of +0.41 e for the hydrogen atom in water.
Walt2001 in Towhee
The official force field name for Walther et al. 2001 in Towhee is 'Walt2001'. Here all of the atom names are listed, along with a brief description.
Please note that the capitalization and spacing pattern is important and must be followed exactly as listed here.
- 'C' : Carbon in a carbon nanotube.
- 'O' : Oxygen in water.
- 'H' : Hydrogen in water.
Coulombic interactions
This force field assigns coulombic interactions to the water molecules.
In the original paper they also used quadrupole moments on the carbon atoms, but they found these had no significant
effect on the results and therefore the quadrupole moment is not included in this implementation.
The 'bond increment' method of charge_assignment is implemented for this forcefield.
This is the complete list of charge transfered between atom pairs when utilizing the 'bond increment' method.
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