Moving constraints feature works in conjunction with the Harmonic Constraints (see an appropriate section of the User's guide). The reference positions of all constraints will move according to
The way the moving constraints work is that the moving reference position is calculated every integration time step using Eq. 30, where is in Å/timestep, and is the current timestep (i.e., firstTimestep plus however many timesteps have passed since the beginning of NAMD run). Therefore, one should be careful when restarting simulations to appropriately update the firstTimestep parameter in the NAMD configuration file or the reference position specified in the reference PDB file.
NOTE: NAMD actually calculates the constraints potential with and the force with , where is the exponent consexp. The result is that if one specifies some value for the force constant in the PDB file, effectively, the force constant is in calculations. This caveat was removed in SMD feature.
The following parameters describe the parameters for the moving harmonic constraint feature of NAMD.