! constrained_md_distance.inp - blue-moon (constrained MD) window: d(Na-Cl) fixed
! at TARGET; the SHAKE Lagrange multiplier gives the mean force.
! Chapter 15, step 3.  Target versions: CP2K 2023.1 ... 2026.2
!
! One window (run it inside its own directory, see run_bluemoon.sh):
!   mpirun -np 64 cp2k.psmp -E TARGET=3.20 -E COORD=start.xyz -i constrained_md_distance.inp -o bm.out
! Output: bluemoon.LagrangeMultLog ("Shake  Lagrangian Multipliers:" lines, a.u.)
! For a single distance constraint: dA/dr = -<lambda>  (hartree/bohr).
! Integrate the windows with: python3 bluemoon_integrate.py window_*/

@SET LEVEL ${LEVEL-dft}
@SET COORD ${COORD-nacl_eq.xyz}
@SET TARGET ${TARGET-2.80}

&GLOBAL
  PROJECT nacl_bm_${LEVEL}
  RUN_TYPE MD
  PRINT_LEVEL LOW
&END GLOBAL

@INCLUDE 'nacl_${LEVEL}_force_eval.inc'

&MOTION
  &MD
    ENSEMBLE NVT
    ! 10000 x 0.5 fs = 5 ps per window (discard the first 1 ps in the analysis)
    STEPS ${STEPS-10000}
    TIMESTEP 0.5
    TEMPERATURE 300.0
    &THERMOSTAT
      TYPE CSVR
      REGION GLOBAL
      &CSVR
        TIMECON 100.0
      &END CSVR
    &END THERMOSTAT
  &END MD
  &CONSTRAINT
    ! apply the constraint to the starting positions/velocities as well
    CONSTRAINT_INIT T
    SHAKE_TOLERANCE 1.0E-8
    &COLLECTIVE
      COLVAR 1
      ! Na and Cl belong to different "molecules"
      INTERMOLECULAR T
      TARGET [angstrom] ${TARGET}
    &END COLLECTIVE
    &LAGRANGE_MULTIPLIERS ON
      COMMON_ITERATION_LEVELS 1
      FILENAME =bluemoon.LagrangeMultLog
    &END LAGRANGE_MULTIPLIERS
  &END CONSTRAINT
  &PRINT
    &TRAJECTORY
      FORMAT XYZ
      &EACH
        MD 10
      &END EACH
    &END TRAJECTORY
    &RESTART
      BACKUP_COPIES 0
      &EACH
        MD 100
      &END EACH
    &END RESTART
    &RESTART_HISTORY OFF
    &END RESTART_HISTORY
  &END PRINT
&END MOTION