<tt>HELM = EPOT + KATOM</tt> in <tt>NVE</tt> ensemble, where <tt>EPOT</tt> is
the potential energy and <tt>KATOM</tt> is the kinetic energy of the atoms.  In other ensembles,
the energies of the thermo-stat and bario-stat are added to <tt>HELM</tt> as well.

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