The velocity keyword

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  • This keyword is used to initialize the velocities of the atoms in the system according to a given temperature.


  • This keyword only has one parameter, which is the initial temperature of the system:
   velocity initial_temperature
  • The temperature is in units of kelvin (K).


Example 1

  • For example, the command
   velocity 10

means that one wants to set the initial temperature to 10 K.


  • The initial velocities generated do not follow the Maxwell distribution, but this is not a problem at all. During the MD simulation, Maxwell distribution will be automatically developed within a short time.
  • The total linear and angular momenta are zeroed.
  • If there are already velocity data in the file, the initial temperature will not be used and the velocities will be initialized as those in the file.

Related keywords

  • None