ls to be shifted by 0.5 a.u.
By default, this level-shifting procedure is switched on whenever the
HOMO-LUMO gap is small.  Small is defined by default to be 0.05 au but
can be modified by the directive <code>hl_tol</code>.  An example of
changing the HOMO-LUMO gap tolerance to 0.01 would be,
<PRE>
  CONVERGENCE hl_tol 0.01
</PRE>

<P>
Direct inversion of the iterative subspace with extrapolation of up to
10 Fock matrices is a default optimization procedure.  For large
molecular systems the amount of availa