Tertiary structure format Textual format Topology format GROMACS itp GROMACS itp files are used also to define position restrictions on the molecule, or to define the force field parameters for a particular ligand. 1.22 GROMACS itp files (include topology) contain structure topology information, and are typically included in GROMACS topology files (GROMACS top). Itp files are used to define individual (or multiple) components of a topology as a separate file. This is particularly useful if there is a molecule that is used frequently, and also reduces the size of the system topology file, splitting it in different parts. FF parameter format