Constrained optimization

During a geometry optimization certain constraints can be enforced with the Constraints key. The constraints refer to the coordinates of the unit cell as specified on input.

Constraints (block-type)

Key to control constraints during a geometry optimization.

Constraints
  Atom a1 {x y z}
  Dist a1 a2 distance
  Angle a1 a2 a3 angle
  Dihed a1 a2 a3 a4 angle
End

Atom: Freeze the position of atom a1 to the current coordinate, or if specified to (x,y,z). This constraint will make the calculation cheaper, because the gradients of frozen atoms need not be calculated.

Dist: Constrain the distance between atoms a1 and a2 to distance

Angle: Constrain the angle between atoms a1, a2, and a3 to angle

Dihed: Constrain the dihedral angle between atoms a1, a2, a3, and a4 to angle