Hi all,

I recently found that extended-Lagrangian algorithms (e.g., eABF) are not compatible with NAMD's new globalMaster MTS. When running an eABF simulation with:

globalMasterFrequency 2
globalMasterScaleByFrequency off
globalMasterStaleForces on

NAMD outputs:

colvars:Detected discrete jump in colvar value from -72.463 to -67.3934.
colvars :Reinitializing extended coordinate to colvar value.
Synchronizing (emptying the buffer of)trajectory file "output/eabf.colvars.traj"
colvars :The restart output state file will be "output/eabf.restart.colvars.state".colvars :colvars:Initializing extended coordinate to colvar value.
colvars:Detected discrete jump in colvar value from -49.7613 to -52.3231.
colvars:Reinitializing extended coordinate to colvar value.
colvars :Initializing extended coordinate to colvar value.
colvars :Reinitializing extended coordinate to last value.Initializing extended coordinate to colvar value.

The values in the .czar.pmf file remain zero. In contrast, plain ABF works well with this new feature (all input files attached:

MTS.tar.gz

).

I suspect this issue arises because NAMD stores the last-step biasing force and performs an additional integration step for the real system, while not for the extended degrees of freedom. Consequently, Colvars detects discrepancies and attempts corrections every two steps. I recommend modifying Colvars to recognize the globalMasterStaleForces on setting, store the previous biasing force, and integrate the extended DOF independently of NAMD's communication.

Best,
Haohao