Velcoities printed are different

Rad rad.... at arl.army.mil
Fri May 16 19:26:37 UTC 2008
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Hi,

I am having some issues with the velocities printed by cp2k when I
restrain some of the atoms. If there are no contraints  on the atoms
everything is fine. Here is my test system which is the basic cell of
quartz:


 &GLOBAL
   BLACS_GRID  SQUARE
   PROGRAM_NAME  CP2K
   PROJECT_NAME QZ
   OUTPUT_FILE_NAME
   RUN_TYPE MD
 &END GLOBAL
 &MOTION
   &MD
     ENSEMBLE  NVE
     STEPS            10
     TIMESTEP     1.000000000000000E+00
     STEP_START_VAL          0
     TIME_START_VAL     0.0000000000000000E+00
     TEMPERATURE        2.4999999999999997E+02
     &PRINT
      &ENERGY  LOW
         &EACH
         &END EACH
         ADD_LAST  NO
         COMMON_ITERATION_LEVELS               1
         FILENAME
       &END ENERGY
     &END PRINT
   &END MD
   &CONSTRAINT
     CONSTRAINT_INIT  T
     &FIXED_ATOMS
       RANGE               1         2
     &END FIXED_ATOMS
   &END CONSTRAINT
   &PRINT
     &TRAJECTORY  ON
       &EACH
       &END EACH
       ADD_LAST  NO
       COMMON_ITERATION_LEVELS               1
       FILENAME ./Trajectory
       FORMAT  DCD
     &END TRAJECTORY
     &VELOCITIES  ON
       &EACH
       &END EACH
       ADD_LAST  NO
       COMMON_ITERATION_LEVELS               1
       FILENAME ./Velocities
       FORMAT  ATOMIC
     &END VELOCITIES
     &FORCES  ON
       &EACH
       &END EACH
       ADD_LAST  NO
       COMMON_ITERATION_LEVELS               1
       FILENAME ./Forces
       FORMAT  ATOMIC
     &END FORCES
     &RESTART  ON
       &EACH
       &END EACH
       ADD_LAST  NUMERIC
       FILENAME ./Restart
     &END RESTART
   &END PRINT
 &END MOTION
 &FORCE_EVAL
   METHOD  QS
   &DFT
     BASIS_SET_FILE_NAME BASIS_SET
     POTENTIAL_FILE_NAME POTENTIAL
     WFN_RESTART_FILE_NAME QZ-RESTART.wfn
     &QS
       EPS_DEFAULT     9.9999999999999998E-13
       EXTRAPOLATION  PS
       EXTRAPOLATION_ORDER               3
       MAP_CONSISTENT T
     &END QS
      &SCF
       &OUTER_SCF
         EPS_SCF 1.0E-6
         MAX_SCF 400
       &END OUTER_SCF
       EPS_SCF 1.0E-6
       MAX_SCF 800
       SCF_GUESS RESTART
       &OT
         ALGORITHM IRAC
         ORTHO_IRAC CHOL
         EPS_IRAC_SWITCH 0.0E0
         STEPSIZE 0.2
         MINIMIZER DIIS
         PRECONDITIONER FULL_ALL
         LINE_SEARCH 2PNT
        &END OT
     &END SCF
    &MGRID
       CUTOFF     3.5000000000000000E+02
       ngrids     80
     &END MGRID
     &XC
      &XC_FUNCTIONAL PBE
      &END XC_FUNCTIONAL
    &END XC
   &END DFT
   &SUBSYS
     &CELL
      a   9.2863         0         0
      b   -4.6432    8.0422         0
      c   0.0000    0.0000   10.2159
       UNITS  BOHR
       PERIODIC  XYZ
     &END CELL
     &COORD
Si    2.3096270     0.0000000     1.8018198
O   1.3722624     1.1392604     1.1590464
Si  3.7592865     2.0001957     3.6038198
O   3.2413404     0.6187839     2.9610464
Si  1.3022365     2.2555398     5.4058198
O   2.7575472     2.4976911     4.7630464
O  -1.0847876     3.1164751     2.4449536
O   0.7842904     3.6369515     0.6429536
O   0.3004972     1.7580443     4.2469536
    &END COORD
    &VELOCITY
      -0.0014980550       -0.0066779880       -0.0040475988
      -0.0047146537        0.0005903303       -0.0057809221
       0.0049371175        0.0038223444       -0.0033497568
       0.0049416358       -0.0080233178        0.0059768701
      -0.0036970191        0.0000658206        0.0064783783
       0.0048819652        0.0082024797        0.0062165905
       0.0003059689        0.0027225216        0.0009931313
       0.0015140755        0.0061435441       -0.0011725176
      -0.0064501110       -0.0047498695       -0.0046052243
   &END VELOCITY
    &KIND Si
      BASIS_SET DZVP-GTH-PADE
      POTENTIAL GTH-PBE-q4
    &END KIND
    &KIND O
      BASIS_SET DZVP-GTH-PADE
      POTENTIAL GTH-PBE-q6
    &END KIND
  &END SUBSYS
&END FORCE_EVAL

==============================
Here are the velocities printed after first few steps:
   0.0000000000        0.0000000000        0.0000000000
        0.0000000000        0.0000000000        0.0000000000
        0.0001492196        0.0001155267       -0.0001012432
        0.0001493561       -0.0002424970        0.0001806451
       -0.0001117388        0.0000019894        0.0001958027
        0.0001475527        0.0002479120        0.0001878904
        0.0000092476        0.0000822856        0.0000300164
        0.0000457615        0.0001856827       -0.0000354382
       -0.0001949483       -0.0001435602       -0.0001391884
        0.0000000000        0.0000000000        0.0000000000
        0.0000000000        0.0000000000        0.0000000000
        0.0037022112        0.0021663196       -0.0013428865
        0.0026770968       -0.0039331674        0.0027624687
       -0.0014660521        0.0003704522        0.0040672976
        0.0023827210        0.0038647293        0.0027223565
       -0.0005098658        0.0002766404        0.0000120226
        0.0002148341        0.0002307208       -0.0002746427
       -0.0042035964       -0.0020710175       -0.0038557247
        0.0000000000        0.0000000000        0.0000000000
        0.0000000000        0.0000000000        0.0000000000
        0.0060867573        0.0035736694       -0.0024650086
        0.0050049755       -0.0066517600        0.0055766291
       -0.0027925297        0.0003268493        0.0062645421
        0.0037869936        0.0065333944        0.0045636561
       -0.0010208999        0.0004594650        0.0000313240
        0.0004144399        0.0003097795       -0.0005309745
       -0.0060724513       -0.0030571033       -0.0054346994
        0.0000000000        0.0000000000        0.0000000000
        0.0000000000        0.0000000000        0.0000000000
        0.0072009491        0.0042207273       -0.0031707617
        0.0064938860       -0.0080925633        0.0075518903
       -0.0035919957        0.0001562621        0.0070745534
        0.0043463448        0.0079422559        0.0055417694
       -0.0015120417        0.0006630426        0.0000730027
        0.0006316587        0.0004584501       -0.0007962065
       -0.0065624467       -0.0034669686       -0.0054704610
============================================
If you compare the initial set of velocities with the ones in the
input, you can see that they are different. Is it a bug in cp2k or the
velocities are converted to a different unit or somehow the velocity
of the center of mass is subtracted?

Could you please look into this and let me know where the issue might
be. I got into this issue on my large system and so I tried it on a
small test system and verify the consistency of the behaviour.

Please let me know if you need any additional information on the test.

Thanks
Rad
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