where 
is a random number between 0 and 1.
is the initial temperature specified through the parameter
FIRStemperature. Alternatively, the velocities can be assigned to a
uniform distribution with width 
(IASVel=UNIForm).
As a third possibility, the initial velocities can be
taken from the atom properties VX, VY, VZ and indicated
by IASVel= CURRent.