OH bond of water elongates after restarting ab initio MD from a classical MD run

[Aman Jindal]

Hello everyone,

I took the NaCl/water system.  I have fixed the NaCl atoms as I am 
interested in only water dynamics.After few ps of classical MD  using FIST 
methods in CP2K, I switched to* ab inito *MD using the restart file from 
the previous run. I saw the trajectory from both the run in VMD, upto 
classical MD everything seems fine, but when I started AIMD the some of the 
O-H bonds in water is highly elongated. I am not able to understand why it 
is happening so ? Motion section of my input file is as follows:

&MOTION
  &CONSTRAINT
  &FIXED_ATOMS
    COMPONENTS_TO_FIX XYZ
    LIST 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 
26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 
101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 
120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 
139 140 141 142 143 144
  &END FIXED_ATOMS
&END CONSTRAINT
 &GEO_OPT
   OPTIMIZER BFGS 
   MAX_ITER  100
   MAX_DR    [bohr] 0.003 
   &BFGS
   &END
 &END
 &MD
   ENSEMBLE NVE  
   TEMPERATURE [K] 330
   TIMESTEP [fs] 0.5
   STEPS 500
 &END
  &PRINT
   &TRAJECTORY
     &EACH
       MD 20
     &END EACH
   &END TRAJECTORY
   &VELOCITIES OFF
   &END VELOCITIES
   &FORCES OFF
   &END FORCES
   &RESTART_HISTORY
     &EACH
       MD 100
     &END EACH
   &END RESTART_HISTORY
   &RESTART
     BACKUP_COPIES 3
     &EACH
       MD 1
     &END EACH
   &END RESTART
  &END PRINT
&END
&EXT_RESTART
  RESTART_FILE_NAME  NaCl-Free-1.restart


I have attached the input file also for the reference. One more problem is 
that this run is taking quite a long time, is there any I can improve the 
speed of the run ?

Thanks in advance,

Aman Jindal

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