This section covers the TIP4P force field for water as it is implemented into the towhee_ff_TIP4P 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. TIP4P is a rigid
water model that has a Lennard-Jones site on the Oxygen and bare charge sites on the Hydrogens and along the
bisector between the hydrogens.
TIP4P is a branched, rigid molecule (when you consider the charged interaction site) and therefore configurational-bias
is currently unable to generate structures so you will need to provide an initial structure and also use the rotational-bias
moves instead of the configurational-bias moves for molecule transfers between simulation boxes.
The Jorgensen group has also parameterized two other water models that utilize different numbers of interaction sites.
Please see the TIP3Pand TIP5P web pages for more information
about those water models. This water model is suitable for use with any Lennard-Jones forcefield, but is
especially well suited for the OPLS family of potentials. Please see the OPLS-ua,
OPLS-aa, and OPLS-2001 web pages for more information.
Any discrepencies (especially typos) from the published force field values are the sole responsibility of
Marcus Martin, and I welcome feedback on how this
implementation compares with other programs.
References for TIP4P
TIP4P was originally published in the following paper
TIP4P in Towhee
The official force field name for TIP4P in Towhee is 'TIP4P'. Here
I list all of the atom names for use in the towhee_input file,
along with a brief description taken from the literature.
Please note that the capitalization and spacing pattern is important and must be
followed exactly as listed here.
- 'H' : hydrogen in water
- 'O' : oxygen in water
- 'M' : charge site 0.15 Angstroms along the bisector between the hydrogens
TIP4P uses atom-centered point charges to represent the electrostatic interactions.
Here are the suggested charge assignments for water.
- 'H': 0.52
- 'O': 0.0
- 'M': -1.04
There are no improper torsions for this force field.
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