# velocities

Specify the initial nuclear cartesian velocities for an MD trajectory. This command can appear in the global context.

### Options

file

Name of the file from which the initial velocities are read.

• The type is string
• There is no default value.
initial

Specify x, y, z components of initial velocities in atomic units. The number of velocities specified must equal the number of atoms in the system.

It may be helpful that one atomic unit of velocity is $$\alpha c$$, where $$\alpha$$ is the fine-structure constant (around $$1/137.036$$) and $$c$$ is the speed of light.

• The type is [(real, real, real)]
• There is no default value.
load

Name of result set from which to load the velocites.

• The type is string
• There is no default value.
rng_seed

Seed used to initialize a pseudo-random number generator. By default, rng_seed is set to -1, which uses a pseudo random seed.

• The type is int
• The default is -1
sampling

Specify the method for sampling the initial velocities.

• The type is string
• There is no default value.
• The value must be one of:
• uniform - Generate uniformly random velocities between [-1, 1] and rescale them to result in the desired temperature.
• thermal - Random sampling of velocities from a Maxwell-Boltzmann distribution at the desired temperature.
scale

Specify whether to scale the initial velocities to the desired temperature (for read-in velocities only).

• The type is bool
• The default is false
temperature

Specify the temperature for sampling the velocities.

• The type is quantity
• The default is 0 kelvin
• The value must be nonnegative