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.
