# Simulation units¶

Most physical quantities carry a dimension, and their numeric values are meaningful only in conjuction with a suitable unit. A computer, on the other hand, processes just plain numbers. The interpretation of such a numeric value as physical quantity depends on the—completely arbitrary—specification of the associated unit. Within a given simulation, the only constraint is that all units are derived from the same set of base units, e.g., for length, time, mass, temperature, and current/charge.

For example, an interaction range “” of the Lennard-Jones potential may be interpreted as , , or even (for argon). Another more abstract interpretation of “” is that all lengths are measured relative to .

Typical choices for base units along with some derived units are given in the table:

physical dimension | symbol | SI base units | cgs system | abstract units (Lennard-Jones potential) |
---|---|---|---|---|

length | L | metre | centimetre | |

time | T | second | second | |

mass | M | kilogram | gram | |

temperature | Θ | kelvin | ||

current | I | ampère | franklin / second | |

energy | M×L²×T⁻² | joule | erg | |

force | M×L×T⁻² | newton | dyne | |

pressure | M×L⁻¹×T⁻² | pascal | barye | |

dynamic viscosity | M×L⁻¹×T⁻¹ | pascal × second | poise | |

charge | I×T | ampère × second | franklin |