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## automodel.nonstd_restraints() -- add restraints on ligands

`nonstd_restraints(aln)`

> This routine adds restraints to keep residues that have no defined topology (generally BLK residues, used to transfer ligands directly from templates, as described in Section 2.2.1) in a reasonable conformation. You can override this method if you need to change these restraints.

> By default, three sets of restraints are built:

- Intra-residue distances are all constrained to their template values. This causes each residue to behave as a rigid body.
- Inter-residue distances are constrained to template values if these are 7Å or less. This has the effect of preserving multiple-HETATM structures such as DNA chains.
- Residue-protein distances are constrained to template values if these are 10Å or less. This preserves ligand coordination.