X-PLOR provides a means to restrain the main coordinate set ( atom properties x,y,z) to the reference coordinate set ( atom properties refx, refy, refz). The restraints are defined as
where the sum extends over all atoms, is individual weights, is the atomic coordinates of the main set, is the atomic coordinates of the reference set, and e is an exponent. The individual weights correspond to the atom property HARM and can be assigned using the vector statement (Section 2.16); the physical dimension of HARM is kcal mole Å. By default, is zero. The reference coordinate set can be assigned using the vector statement or by using the DISPosition option of the coordinate statement. The exponent e is set by using the restraints harmonic statement.