Set the scaled coordinates of all atoms to be random numbers uniformly distributed
in [-0.5, 0.5).  This can be used to initialize the configuration for gas or liquid
simulation.  Because some atoms may accidentally get too close to each other (leading
to very high energy and repulsive forces), <tt>relax</tt> usually is necessary before
MD simulation (<tt>run</tt>).

<p>
Also see <tt>initvelocity</tt>.
