Current step number in conjugate gradient relaxation <tt>relax</tt>, 
equivalent to <tt>curstep</tt> in MD simulation <tt>run</tt>.

<p>
It is used to determine when whether the X-window needs to be 
refreshed, or intermediate .cn file needs to be saved, at the current 
simulation step.

<p>
Also see <tt>plotfreq</tt>, <tt>savecnfreq</tt>.
