How to make dihedral force constant in CB9H10 cage boron cluster

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GROMACS version: 2024.4
GROMACS modification: No

Hello, I’m working on parameterizing the carborane molecule CB9H10 (C1B9H10) for molecular dynamics in GROMACS. I’m following the OPLS-AA force field format and successfully generated most bonded and nonbonded parameters. However, defining the dihedral force constants has been challenging due to the unique boron cage structure.

I’ve tried:

  • Using [dihedrals] with type 9 (Ryckaert-Bellemans) for torsions across the cage.
  • Fitting QM torsion scan data from Gaussian.
  • ACPYPE, LigParGen, and Poltype2, but they don’t work well for boron atoms.

Is there a recommended workflow or tool for assigning dihedrals for boron-rich molecules like CB9H10? Any advice or shared experience would be greatly appreciated.

Thank you!