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Re: [lammps-users] problem about “velocity” command
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Re: [lammps-users] problem about “velocity” command


From: Axel Kohlmeyer <akohlmey@...24...>
Date: Wed, 23 May 2018 22:41:21 -0400



On Wed, May 23, 2018 at 10:17 PM, 吴胜 <ws930819@...6040...> wrote:
Dear all,
      Something confused me about the “velocity” command. I used the command  "velocity all create 300.0 492845 rot yes dist gaussian"  to distribute velocity to all the molecular. According to my understanding , the velocity should be distributed randomly obeying gaussian distribution. Namely if i do the same simulation twice, the result should be different because the  velocity of molecular should be different.

​this is where you go wrong. if you use the *exact* same input and the same number of CPU cores, the result should be the same. to get a different set of (pseudo!) rand​om numbers, you have to use a different seed value.

axel.

 But according to my result, i find that if the calculation is  made in the same computer using the same cores, the result is the same. So that confused me a lot, how can  the “velocity” command  distribute the velocity?  and can it remain unchanged in the same input?
                                                                                                                                                                                                                                         Yours sincerely
                                                                                                                                                                                                                                         David bootman.


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--
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.