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     { TORSION  } [DELETE] repeat(iupac iupac iupac iupac)
     { DIHEDRAL }

The TORSION command, and its synonym, DIHEDRAL, are used to specify torsion angles in a residue. Each quadruple of iupac names specifies a torsion angle with the middle pair of atoms defining the bond being rotated (and used to chose parameters). When the parameter file contains dihedral angles specified by all four atoms, every dihedral angle is first checked to see if it matches any of this type. If so, then the four atom parameters values are used. If a particular four atom dihedral is specified twice in adjacent positions, then it is assumed that the corresponding parameter file specifies two separate parameter values for this four atom dihedral, and both will be used.

The RTF Generate Command, see RTF Generate Command, can be used to generate the torsion angles within a residue automatically, but torsion angles involving atoms outside the current residue must always be specified “by hand”.

The DELETE option causes CONGEN to delete the named torsion angles from the current residue. This option is useful when the COPY command or the automatic generation of torsion angles is used.