`The constraints parameters are specified in the same manner as for
usual (static) harmonic constraints. The reference positions of all
constrained atoms are then rotated with a given angular velocity
about a given axis. If the force constant of the constraints is
sufficiently
large, the constrained atoms will follow their reference positions.
`

`A rotation matrix
about the axis unit vector
is calculated every
timestep
for the angle of rotation corresponding to the current timestep.
angle =
,
where
is the angular velocity of rotation.
`

`From now on, all quantities are 3D vectors, except the matrix
and the
force constant
.
`

`The current reference position
is calculated from the initial
reference
position
(at
),
,
where
is the pivot point.
`

`Coordinates of point N can be found as
.
Normal from the atom pos to the axis is, similarly,
normal
The force is, as usual,
;
This is the force applied to the atom in NAMD (see below).
NAMD does not know anything about the torque
applied. However, the torque applied to the atom can be calculated
as a vector product
torque
Finally, the torque applied to the atom with respect to the axis
is the projection of the torque on the axis, i.e.,
`

`If there are atoms that have to be constrained, but not moved,
this implementation is not suitable, because it will move all
reference positions.
`

`Only one of the moving and rotating constraints can be used at a
time.
`

`Using very soft springs for rotating constraints leads to the system
lagging behind the reference positions, and then the force is applied
along a direction different from the "ideal" direction along the
circular path.
`

`Pulling on N atoms at the same time with a spring of stiffness K
amounts to pulling on the whole system by a spring of stiffness NK,
so the overall behavior of the system is as if you are pulling with a
very stiff spring if N is large.
`

`In both moving and rotating constraints the force constant that you
specify in the constraints pdb file is multiplied by 2 for the force
calculation, i.e., if you specified
in the pdb
file,
the force actually calculated is
.
SMD feature of namd2 does the calculation without multiplication of
the
force constant specified in the config file by 2.
`

Are rotating constraints active`rotConstraints`**Acceptable Values:**`on`or`off`**Default Value:**`off`**Description:**Should rotating restraints be applied to the system. If set to`on`, then`rotConsAxis`,`rotConsPivot`and`rotConsVel`must be defined. May not be used with`movingConstraints`.Axis of rotation`rotConsAxis`**Acceptable Values:**vector (may be unnormalized)**Description:**Axis of rotation. Can be any vector. It gets normalized before use. If the vector is 0, no rotation will be performed, but the calculations will still be done.Pivot point of rotation`rotConsPivot`**Acceptable Values:**position in Å**Description:**Pivot point of rotation. The rotation axis vector only gives the direction of the axis. Pivot point places the axis in space, so that the axis goes through the pivot point.Angular velocity of rotation`rotConsVel`**Acceptable Values:**rate in degrees per timestep**Description:**Angular velocity of rotation, degrees/timestep.