velocity

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

Syntax

  • This keyword can be used in the following ways:

    velocity <initial_temperature>
velocity <initial_temperature> seed <seed_number>

  • The temperature is in units of kelvin (K).

  • You can specify a seed for the random number generator to generate a fixed temperature distribution, which is optional. If not specified, the velocities are initialized differently each time.

Example

The command:

velocity 10

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

Caveats

  • The initial velocities generated in this fashion do not obey the Maxwell distribution. This is, however, not a problem since during the MD simulation, the Maxwell distribution will be achieved automatically within a short time.

  • The total linear and angular momenta are set to zero.

  • If there are already velocity data in the simulation model file, the initial temperature will not be used and the velocities will be initialized as those in the simulation model file.

  • If there are not velocity data in the simulation model file, and this keyword is missing, velocities will be initialized with a default temperature of 300 K.