**RESTraints****DIHEdral { restraints-dihedral-statement } END**is invoked from the main level of X-PLOR. Invocation automatically turns on the CDIH energy flag (Section 4.5).**restraints-dihedral-statement:==**-
**ASSIgn****selection selection selection selection**adds a new dihedral angle to the restraints-dihedral database. The four selections have to be unique; i.e., each selection must select exactly one atom. The selections determine the four atoms that specify the dihedral angle. The first real number specifies the energy constant () in kcal mole rad, the second real number specifies the angle in degrees to which the dihedral angle is restrained (), the third real number specifies the range around the restrained angle (), and the integer number specifies the exponent ().

real real real integer**NASSign=integer**- is a required parameter that specifies the maximum expected number of assignments. It has to be greater than or equal to the actual number (default: 400).
**RESEt**- erases the restraints-dihedral database.
**SCALe**- specifies the overall weight factor .