Multiple Time Stepping User Defined Forces

User defined forces are applied at every time step, unless the user specifies otherwise. The following options provide a variety of ways to control how frequently all user defined forces are applied. These apply to : colvars, tclforces, and any other forces controlled by the GlobalMaster infrastructure.

These apply a Multiple Time Stepping approach to globalmaster forces, where the user controls the length of the new outer step and how the forces are integrated (scaled, or stale) using the parameters defined below.

Please note that this feature is only available in GPU-resident version of NAMD (NAMD3).

• globalMasterFrequency $<$ time steps between invoking global master $>$
  Acceptable Values: positive integer
  Default Value: 1
  Description: Controls the number of steps between invocations of globalmaster clients (i.e., colvars) therefore globalmaster clients will be called on step % globalMasterFrequency == 0. The step number reported to the clients will be standard NAMD time step. globalMasterStep will contain step / globalMasterFrequency so that clients can distinguish between the two.

• globalMasterScaleByFrequency $<$ scale globalmaster forces by frequency? $>$
  Acceptable Values: on or off
  Default Value: off
  Description: Will apply the globalMasterFrequency value as a factor on the force contribution from the globalmaster clients when the new computation is triggered.

• globalMasterStaleForces $<$ are stale forces on or off? $>$
  Acceptable Values: on or off
  Default Value: off
  Description: Will use the last computed value from the globalmaster clients for the force integration on the off steps, instead of the RESPA approach of applying the force once, as a single impulse. This should not be used if globalMasterScaleByFrequency is in use.