How do I handle "Invalid order for directive defaults" in Gromacs

Dear All,

I am doing an MD simulation of peptide and an mRNA using OPLSAA and amber14sb_OL15 force fields respectively.
When I perform the grompp command following error was generated. (see attached screen capture)
Can anyone support me to handle this error?
(I also attached my .top file) (1.1 KB)

You can’t use multiple force fields for the same simulation. The [defaults] directive is the master instruction list for how the functional form is interpreted and applied. You have two of these, one from OPLS and one from AMBER. This can never work. Choose one force field and use it.

@jalemkul Thank you for your reply .