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

[Vladimir Rybkin]

Hi Aman Jindal,

1) it's in principle OK, that different methods give different results. 
Thus, how much are the bonds elongated?

2) You have a redundant &GEO_OPT section in your &MOTION. It does not harm, 
but is confusing.

Yours,

Vladimir

вторник, 6 декабря 2016 г., 17:34:13 UTC+1 пользователь Aman Jindal написал:
>
> 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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