Different angle style, dihedral style, and improper style for MOF and guest moleucle

LAMMPS LAMMPS Beginners
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1

Hi,
I have a problem to combine dihedral_style and improper_style for both MOF and guest molecule. I want to calculate the mean square displacement for 1-phenylamine in UMCM-1. However, the bond style, angle style, dihedral style, and improper style for MOF generated by lammps-interface is different with 1-phenylamine generated by LigParGen (OPLS-AA force field).

Input file for MOF:
units real
atom_style full
boundary p p p

pair_style lj/cut/coul/long 12.500
bond_style harmonic
angle_style hybrid fourier cosine/periodic
dihedral_style harmonic
improper_style fourier
kspace_style ewald 0.000001

special_bonds lj/coul 0.0 0.0 1.0
dielectric 1.0
pair_modify tail yes mix arithmetic
box tilt large
read_data data.UMCM1

Input file for 1-phenyamine by Ligpargen server:
units real
atom_style full

dimension 3
boundary p p p

pair_style lj/cut/coul/cut 20.0 20.0
pair_modify mix geometric

bond_style harmonic
angle_style harmonic
dihedral_style opls
improper_style cvff
special_bonds lj/coul 0.0 0.0 0.5

read_data 1phenylamine.lmp

They have different angle_style, dihedral_style, and improper_style. How can I combine my guest molecule and MOF to simulate the MSD with different angle, dihedral, and improper styles?
Thanks

2

Please check out using the angle, dihedral, and improper style hybrid.

Please also note that mixing different force fields is often considered problematic and can lead to inconsistent results.

3

You mean if I use UFF for MOF, I would better use same force field for my guest molecule? But I think UFF is not accurate; my guest molecule is just an small organic molecule (1-phenylamine) so there is no metal atom inside. I think if I can avoid to use UFF, I would choose a better force field for organic molecules.

4

I cannot answer this for this particular case since this is not my area for research. Usually, the reliability of a force field and its parameters depends strongly on how specific those are. The more specific, the less transferable but the more consistent and accurate.

The ideal situation would be to have a consistent parameterization for all atoms. If that doesn’t exist, you should see to find something that is compatible. Please also note that there are forces fields specific for MOFs and that part is usually more critical than getting the parameters for a small organic molecule. In classical force fields, the situation usually becomes increasingly problematic with the polarity of the components.