Kinetic energy change

[LS]

Hi,

I am trying to run a NVE simulation of an atom impinging on a cluster. I find that even within 1 time step, the kinetic energies of the atom is changing quite a bit. So, I simply tried to put one atom in a box (with a certain velocity) and run the same NVE simulation. Even then I find the kinetic energy changing in just 1 time step. Is there some problem with my input file? Any help is appreciated.


&GLOBAL
  PROJECT Na-md
  RUN_TYPE MD
  PRINT_LEVEL MEDIUM
  WALLTIME 1.40000000E+04
&END GLOBAL


&MOTION
  &MD
    ENSEMBLE NVE
    STEPS 100000
    TIMESTEP 0.5
   &PRINT
     FORCE_LAST .TRUE.
   &END PRINT
   &END MD
  &PRINT
  &RESTART
  ADD_LAST NUMERIC
  &END RESTART
  &VELOCITIES
  ADD_LAST NUMERIC
  &END VELOCITIES
  &END PRINT
 &END MOTION


&FORCE_EVAL
  METHOD Quickstep
  &DFT
    BASIS_SET_FILE_NAME ~/cp2k/tests/QS/GTH_BASIS_SETS
    POTENTIAL_FILE_NAME ~/cp2k/tests/QS/POTENTIAL
    UKS
    &MGRID
      CUTOFF 400
      NGRIDS 4
      REL_CUTOFF 25
    &END MGRID
    &QS
      EPS_DEFAULT 1.0E-12
      EPS_GVG 1.0E-6
      EPS_PGF_ORB 1.0E-6
    &END QS
    &SCF
    EPS_SCF 1.0E-6 
    MAX_SCF 500
      SCF_GUESS atomic
      &OT ON
        MINIMIZER DIIS
       PRECONDITIONER FULL_ALL
      &END OT
    &END SCF
    &XC
      &XC_FUNCTIONAL BLYP
      &END XC_FUNCTIONAL
    &END XC
   &POISSON
   POISSON WAVELET
   PERIODIC NONE
   &END POISSON
  &END DFT
  &SUBSYS
   &TOPOLOGY
    &CENTER_COORDINATES T
    &END CENTER_COORDINATES
    &END TOPOLOGY
    &CELL
      PERIODIC NONE
      ABC 30.000 30.000 30.000
    &END CELL
     &COORD
Na  -22.000000000000000        0.0000000000000000        0.0000000000000000
     &END COORD
    &VELOCITY
   0.0020569591937   0.0000000000000   0.0000000000000
   &END VELOCITY
    &KIND Na
      BASIS_SET DZVP-GTH
      POTENTIAL GTH-BLYP-q9
    &END KIND
  &END SUBSYS
&END FORCE_EVAL

Thanks a lot in advance.
LS