It is possibile to apply restraints to an individual atom based on its distance from a plane defined by the normal vector and the atom's reference coordinate ( atom properties refx, refy, refz). An atom for which plane restraints are defined experiences restraints only in the direction of . Plane restraints are defined as
where the sum extends over all atoms with negative individual weights . The symbols in Eq. 7.2 correspond to those in Eq. 7.1. By default, plane restraints are turned off. To enable plane restraints, a nonzero normal vector has to be specified using the restraints harmonic statement and assigning a negative weight for the atom property HARM. Note that plane restraints are computed only for atoms with ; otherwise point restraints (see Section 7.1.1) are applied, even if a nonzero normal vector is defined. This permits the simultaneous use of point and plane restraints, however, for disjunct sets of atoms. If , plane restraints are disabled.