Add an improper dihedral between four atoms with the given indices. No checking for duplicate impropers is performed.

  • i (int) – Index of first atom
  • j (int) – Index of second atom
  • k (int) – Index of third atom
  • l (int) – Index of fourth atom
  • molid (int) – Molecule ID to add dihedral in. Defaults to top molecule.
  • type (str) – Angle type. Can be from output of topology.getangletypes(), or can define a new angle type. Defaults to None

(int) New number of improper dihedrals defined in system