MMPBSA for custom atom types

GROMACS version:2024.3
GROMACS modification: No
Hi all. Could you please help me with mmpbsa tool for interaction energy analysis. I performed simulation of a protein with tio2 nanoparticle in charmm27 ff. Now I need to process the data with mmpbsa, but encountered a problem with custom atom types (Ti and O atoms of the NP), namely how to indicate their parameters properly to get correct prmtop file?