The SHAKE method (Ryckaert, Ciccotti, and Berendsen 1977) constrains distances between atoms to certain reference distances. In this way, one can constrain bond lengths or angles by constraining the distance between the first and the third atoms of the angle (ijk). The shake statement is used to set up the database for the SHAKE constraints. SHAKE constraints are active during minimization or molecular dynamics, or they can be explicitly imposed by the SHAKE option of the coordinate statement. At present, SHAKE constraints cannot be used during rigid-body minimization.