This section covers the Richards et al. 1995 (Richar1995) force field as it is implemented into the towhee_ff_Richar1995 file in the
ForceFields directory. This force field was designed to reproduce the adsorption behavior of N2 and O2 in Zeolite Li-X.
Note that this is a Lennard-Jones force field that uses the 'explicit' mixing rules, and therefore is not easily combined with other forcefields.
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.
Reference for Richards et al. 1995
This forcefield is described in a single paper.
Typos and comments for Richards et al. 1995
Richards et al. 1995 in Towhee
- I have been unable to reproduce the results shown in Figure~4 and have observed substantially higher adsorption for both
N2 and O2 using this implementation. Either the Lithium ion placement is crucial for adsorption in this zeolite, or
there is an error in the results presented in their paper. Either way, the user is advised to use caution with this forcefield and if anyone
is able to reproduce those results please let the developers know.
The official force field name for Richards et al. 1995 in Towhee is 'Richar1995'. Here is the list of atom names for use in the towhee_input
file, along with a brief description. Please note that the capitalization and spacing pattern is important and must be followed exactly as listed here.
Note that both N2 and O2 are modelled with three interaction sites in this potential.
- 'O' : Oxygen in O2 that is bonded to the midpoint site 'mp'
- 'N' : Nitrogen in N2 that is bonded to the midpoint site 'mp'
- 'Si' : Silicon in zeolite Li-X
- 'Al' : Aluminum in zeolite Li-X
- 'Oz' : Oxygen in zeolite Li-X
- 'Li' : Lithium in zeolite Li-X
- 'mp' : the midpoint charge site of either O2 or N2
This force field uses point charges and has been set up to assign the point charges using the bond increment method.
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