units command

Syntax:

units style 

• style = cgs or si

Examples:

units cgs 

Description:

This command sets the style of units used for a simulation. It determines the units of all quantities specified in the input script and various input files read by SPARTA, as well as the units of all quantities output to the screen, log file, dump files, and other output files. Typically, this command is used at the very beginning of an input script.

IMPORTANT NOTE: Internally, this command simply sets the numeric values of conversion factors used by SPARTA, e.g. the Boltzmann constant used to convert temperature to energy. It is up to you to insure that all input values used in the input script and other input files (surface data, species files, reaction files) contain numeric values consistent with the chosen units.

For style cgs, these are the units:

• mass = grams
• distance = centimeters
• area = cm^2
• volume = cm^3
• time = seconds
• energy = ergs
• velocity = centimeters/second
• acceleration = centimeters/second^2
• pressure = barye (dyne/cm^2 = 0.1 pascals)
• magnetic moment = ??
• temperature = degrees K

For style si, these are the units:

• mass = kilograms
• distance = meters
• area = m^2
• volume = m^3
• time = seconds
• energy = Joules
• velocity = meters/second
• acceleration = meters/second^2
• pressure = pascals (newton/meter^2)
• magnetic moment = ??
• temperature = degrees K

The units command also sets a default timestep size; see the timestep command to change this value.

• For style cgs this is dt = 1.0 sec.
• For style si this is dt = 1.0 sec.

Restrictions:

This command must be used before the simulation box is defined by a create_box command.

Related commands: none

Default:

units si