ab initio md of lithium fluoride

[Michael Mitchell]

Hello all:
I'm a newbie from the classical MD world. Recently, I've been attempting to 
run QS dynamics on the rock salt structure of LiF at 300K to get my feet 
wet. My simulations are on the 2x2x2 supercell of the cubic crystal 
structure. The simulation runs and the thermodynamic properties (temp, 
energy etc) are all converged after an initial equilibration, however the 
system melts, transforming from the rock salt structure into an amorphous 
blend after only 1ps or so of dynamics. Since this structure has been 
simulated before with QS, I must be doing something wrong. Can anybody see 
anything obviously wrong with the following input?

Best,
Mike

============================================================================================
@SET MD_SAVE_FREQ  1
@SET LA 8.2
@SET LB 8.2
@SET LC 8.2
@SET RTEMP 298
@SET PREFIX LiF.2x2x2
@SET NSTEPS 10000

&GLOBAL
 PRINT_LEVEL medium
 PROJECT ${PREFIX}.${RTEMP}
 RUN_TYPE MD
 WALLTIME 36000000
&END GLOBAL

&MOTION
 &CELL_OPT
  EXTERNAL_PRESSURE 1.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 1.0
  KEEP_ANGLES TRUE
  OPTIMIZER BFGS
  TYPE MD
  &PRINT
   &CELL
    FILENAME ./${PREFIX}.${RTEMP}K
    &EACH
     CELL_OPT ${MD_SAVE_FREQ}
    &END EACH
   &END CELL
  &END PRINT
 &END CELL_OPT

 &PRINT
  &VELOCITIES
   FILENAME ./${PREFIX}.${RTEMP}K
   FORMAT XYZ
   &EACH
     MD ${MD_SAVE_FREQ}
   &END EACH
  &END VELOCITIES
  &TRAJECTORY
   FILENAME ./${PREFIX}.${RTEMP}K
   FORMAT XYZ
   &EACH
     MD ${MD_SAVE_FREQ}
   &END EACH
  &END TRAJECTORY
 &END PRINT
 &MD
  ENSEMBLE NVT
  STEPS ${NSTEPS}
  TIMESTEP 0.5
  TEMPERATURE ${RTEMP}
  &LANGEVIN
   GAMMA 0.0001
  &END LANGEVIN
  &THERMOSTAT
   REGION MOLECULE
   TYPE NOSE
   &NOSE
    LENGTH 3
    YOSHIDA 3
    TIMECON 100
   &END NOSE
  &END THERMOSTAT
 &END MD
&END MOTION

&FORCE_EVAL
 METHOD Quickstep
 &DFT
  CHARGE 0
  MULTIPLICITY 1
  WFN_RESTART_FILE_NAME ${PREFIX}.${RTEMP}.md.wfn.restart
  BASIS_SET_FILE_NAME /global/home/users/mike/codes/cp2k/tests/QS/BASIS_SET
  POTENTIAL_FILE_NAME 
/global/home/users/mike/codes/cp2k/tests/QS/GTH_POTENTIALS
  &MGRID
   CUTOFF [Ry] 320
  &END MGRID
  &PRINT
   &MULLIKEN
    FILENAME ./${PREFIX}.${RTEMP}
    &EACH
     MD 1
    &END EACH
   &END MULLIKEN
  &END PRINT

  &QS
   EPS_DEFAULT 1.0E-12
   EXTRAPOLATION ASPC
   EXTRAPOLATION_ORDER 3
   MAP_CONSISTENT
   METHOD GPW
  &END QS
  &SCF
   EPS_SCF 1.0E-5
   MAX_SCF 50
   SCF_GUESS ATOMIC
   &DIAGONALIZATION
    ALGORITHM DAVIDSON
   &END DIAGONALIZATION

   &OUTER_SCF
    EPS_SCF 1.0E-5
    MAX_SCF 20
   &END OUTER_SCF

   #&OT
   # MINIMIZER DIIS
   # PRECONDITIONER FULL_ALL
   #&END OT
  &END SCF
  &XC
   &XC_FUNCTIONAL PADE
   &END XC_FUNCTIONAL
  &END XC

  &POISSON
   PERIODIC XYZ
   POISSON_SOLVER PERIODIC
  &END POISSON
 &END DFT
 &SUBSYS
  &CELL
   ABC ${LA} ${LB} ${LC}
   PERIODIC XYZ
  &END CELL

  &COORD
   @INCLUDE ${PREFIX}.cp2k.xyz
   SCALED .TRUE.
  &END COORD

  &KIND Li
   BASIS_SET DZV-GTH-PADE
   POTENTIAL GTH-PADE-q3
   #BASIS_SET DZVP-GTH-PADE
   #POTENTIAL GTH-PADE-q3
  &END KIND
  &KIND F
   BASIS_SET DZVP-GTH-PADE
   POTENTIAL GTH-PADE-q7
  &END KIND
 &END SUBSYS
&END FORCE_EVAL

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