Amber FF

thank you for your detailed answer. Actually, it is a little difficult for
me to use moltemplate for my molecule( [BMIM][PF6] ionic liquid), since the
examples of moltemplate for Amber are not really helpful for my molecule(
with atm_style full). Could you please send me some example or tutorial
about amber for a bigger molecule.
Best regards

   This is a legitimate point. I made the AMBER force field available, but
I do not use it for my own work. So I do not have the time to make more
examples and test them, aside from the few that are already there.

   I would love to solve this problem by crowdsourcing. I would love to
encourage people to submit their example molecules in moltemplate (or even
LAMMPS) format. If they do (either by email, or by github), I will include
them with moltemplate. If it would help to put a button on the moltemplate
web page along with a web form, I am happy to do that.

   For now, if you do not mind switching force fields, then try the ATB
database. It contains molecule force field parameters and partial charges
for a huge variety of organic molecules in moltemplate (.LT) format. I
think it is free (for academic use). These molecules are presumably not
compatible with the AMBER force field.

https://atb.uq.edu.au/

BMIM is currently here:
https://atb.uq.edu.au/molecule.py?molid=1699
(however they may change the URL in the future. If so, enter "BMIM" into
the search page)

Click on "Molecular Dynamics (MD) Files", and select "LAMMPS" from the
"Format" pull-down menu.

Cheers
Andrew