The lock record defines N_set sets of atoms that may be locked during a simulation. The lock record in the descriptor file has the form

lock	Nset
	Nlock
		atomi	atomj	...
	...

The lock record starts with the keyword lock followed by the number of lock sets N_set. This is followed by N_set sub-records consisting first of the number of atoms in the lock set N_lock then the atoms in the set atom_i, atom_j, atom_k and so on.

The lock sets are dormant until a set is selected during a simulation. When a lock set is selected before the application of certain simulation methods, the atoms in the set are locked into their current positions (whatever that may be). The lock-friendly methods are Monte Carlo and some energy minimization methods. If other simulation methods (molecular dynamics in particular and some energy minimization methods) are used the locked atoms will move along with every other atoms, i.e., the locks will have no effect. When a lock-friendly simulation method is applied later on, the atoms in the chosen lock set are locked at their new positions. Choosing lock set 0 removes all atom locking. Example

lock   3

3
     9   17   18
10
     3   6   7   8   9   11   16   17   18   19
7
     7   8   9   11   17   18   19

Three lock sets are defined with three, ten and seven candidate atoms respectively. In a simulation, one could for example, choose lock set 2, then 3, then 1 and finally 0 to refine a system with most of the atoms locked in the beginning and then to progressively relax the constraints until with the final choice of lock set 0, all atoms are released.