! nacl_dissociation_wtmetad.inp - well-tempered metadynamics of NaCl dissociation
! in water, biasing the Na-Cl distance (COLVAR 1).  Chapter 15, step 2.
! Target versions: CP2K 2023.1 ... 2026.2 (native CP2K metadynamics, no PLUMED)
!
! Needs nacl_eq.xyz from nacl_equil.inp.  Default level: PBE-D3(BJ).
!   mpirun -np 64 cp2k.psmp -i nacl_dissociation_wtmetad.inp -o wtmetad_dft.out
! Cheap pre-sampling with GFN1-xTB (100 ps):
!   mpirun -np 16 cp2k.psmp -E LEVEL=xtb -E STEPS=200000 -i nacl_dissociation_wtmetad.inp -o wtmetad_xtb.out
! Output: nacl_wtmetad_<LEVEL>-COLVAR.metadynLog, nacl_wtmetad_<LEVEL>-HILLS.metadynLog
! Free-energy profile: python3 fes_from_hills.py nacl_wtmetad_dft-HILLS.metadynLog --bohr2ang
! Continue a run: uncomment &EXT_RESTART (hills are stored in the restart file).

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

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

! &EXT_RESTART
!   RESTART_FILE_NAME nacl_wtmetad_dft-1.restart
! &END EXT_RESTART

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

&MOTION
  &MD
    ENSEMBLE NVT
    ! 40000 x 0.5 fs = 20 ps (DFT); use far more for converged profiles
    STEPS ${STEPS-40000}
    TIMESTEP 0.5
    TEMPERATURE 300.0
    &THERMOSTAT
      TYPE CSVR
      REGION GLOBAL
      &CSVR
        TIMECON 100.0
      &END CSVR
    &END THERMOSTAT
  &END MD
  &FREE_ENERGY
    METHOD METADYN
    &METADYN
      DO_HILLS T
      ! one Gaussian every 40 MD steps (20 fs)
      NT_HILLS 40
      ! initial Gaussian height in hartree (4.0E-4 Ha = 1.05 kJ/mol)
      WW 4.0E-4
      ! well-tempered: bias factor gamma = (T + DELTA_T)/T = (300 + 1500)/300 = 6
      WELL_TEMPERED T
      DELTA_T 1500.0
      &METAVAR
        COLVAR 1
        ! Gaussian width in INTERNAL units: bohr for a distance (0.35 bohr = 0.185 A)
        SCALE 0.35
        ! keep d(Na-Cl) below ~5.6 A (< L/2 = 6.21 A of the 12.42 A box)
        &WALL
          TYPE QUADRATIC
          ! wall position in bohr (10.6 bohr = 5.61 A)
          POSITION 10.6
          &QUADRATIC
            DIRECTION WALL_PLUS
            ! K*(CV - POSITION)^2, K in hartree/bohr^2
            K 0.05
          &END QUADRATIC
        &END WALL
      &END METAVAR
      &PRINT
        &COLVAR
          COMMON_ITERATION_LEVELS 3
          &EACH
            MD 1
          &END EACH
        &END COLVAR
        &HILLS
          COMMON_ITERATION_LEVELS 3
          &EACH
            MD 1
          &END EACH
        &END HILLS
      &END PRINT
    &END METADYN
  &END FREE_ENERGY
  &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