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