[gmx-users] Regarding engineered residue topology

[Venkat Reddy]

Dear all,
I am trying to simulate a peptide with engineered residues like Aib (alpha
amino-isobutyric acid). I am trying to use OPLS-aa forcefield. Though
everything went well initially during topology generation, grompp showed
the following error.

ERROR 1 [file topol.top, line 2316]:
  No default Ryckaert-Bell. types
ERROR 2 [file topol.top, line 2317]:
  No default Ryckaert-Bell. types
ERROR 3 [file topol.top, line 2318]:
  No default Ryckaert-Bell. types
ERROR 4 [file topol.top, line 2325]:
  No default Ryckaert-Bell. types
ERROR 5 [file topol.top, line 2326]:
  No default Ryckaert-Bell. types
ERROR 6 [file topol.top, line 2327]:
  No default Ryckaert-Bell. types

The cross-check with topolo.top identified the dihedral CB2-CA-CB1-HB11 is
throwing the error. My question is, even though the parameters for Aib are
available in OPLS ff, why I am getting this error?

Please help me in this regard

With regards
Venkat