2.1 Units

To avoid the handling of small numbers, choose units appropriate to the model.

Lennard-Jones: Energy unit ; length . The pair energy is then

where and .

As the third mechanical unit, choose the atomic mass .

The time unit is now the combination .

Electrical charge: best measured in multiples of the electron charge, .

Number density: is a large number; therefore we reduce it by a suitable standard density, : .

Temperature:

Hard spheres: no natural'' unit of energy; therefore choose self-consistent time unit .

For hard spheres of diameter the customary standard density is ; thus: .
F. J. Vesely / University of Vienna