Is the number of impropers dependent on the force-field?

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Dear users,#### I have built a polymer system using accelrys materials studio and converted it to the lammps data file using msi2lmp and pcff and cvff force fields. checking the created data files, I found that the numbers of impropers were different for two force fields. Is the number of impropers dependent on the force-field used? I know that the number of atom types is different for different FF, but I wonder if this affect the number of impropers?#### Thanks,

Behrouz

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Dear users,

I have built a polymer system using accelrys materials studio and converted
it to the lammps data file using msi2lmp and pcff and cvff force fields.
checking the created data files, I found that the numbers of impropers were
different for two force fields. Is the number of impropers dependent on the
force-field used? I know that the number of atom types is different for

yes and no. class 2 force fields have many additional bonded terms.
the number may also depend on what you have in your frc file

different FF, but I wonder if this affect the number of impropers?

if you use the msi2lmp that comes with the very latest version of
LAMMPS, you can use the -p flag to raise the print level and follow in
detail what is happening during the conversion.

older versions of msi2lmp also have bugs when it comes to impropers.
as far as i could track down, one of these bugs had been around since
2006, probably longer.

axel.