General OPLS-AA parameters for unspecified atom types

Hi all,

I am trying to run simulations for a set of ionic liquids using LAMMPS. I have a list of SMILES of my ionic liquids, and I am using the python package foyer (GitHub - mosdef-hub/foyer: A package for atom-typing as well as applying and disseminating forcefields) for automatic atom-typing. However, for some ions, e.g. BF4, PF6, AlCl4, the parameters of bonds (e.g. B-F, P-F, Al-Cl), angles, and dihedrals are not provided in OPLS. I cannot run simulations without these parameters.

I learned that it is very time-consuming and tricky to do force field parameterisation for new atom types. In this case, may I ask if there are any “generalized” parameters in OPLS-AA for unspecified atom types, for example, bond parameters for “atom:X - atom:X” ?

Thank you!

Do what I do and coarse grain the lot of them. [evil smile]

More seriously, there’s plenty of published OPLS-AA simulations of ionic liquids, and these are quite common anions. Why not look at literature? Alternatively, you can use the Automated Topology Builder and see what it spits out (although you need to be at least self consistent and use it for your cations as well).

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You are asking in the wrong place. LAMMPS just runs simulations.
You need to ask people that maintain or develop force fields or related tools.
For ionic liquids there also are specialized parameters, so you may also want to search the published literature for them and there may be some that are compatible with OPLS/AA.