Updated UMP convergence figure

Manuscript/EPAWTFT.tex

@@ -950,7 +950,8 @@ sacrificed convergence of the excited-state series so that the chance of ground-
 
 Since the UHF ground state already provides a good approximation to the exact energy, the ground-state sheet of
 the UMP energy is relatively flat and the corresponding EP in the Hubbard dimer always lies outside the unit cylinder.
-\hugh{The slow convergence observed in \ce{H2} can then be seen as this EP moves ever closer to one at larger $U/t$ values.}
+\hugh{The slow convergence observed in \ce{H2}\cite{Gill_1988} can then be seen as this EP 
+moves closer to one at larger $U/t$ values.}
 Furthermore, the majority of the UMP expansion in this regime is concerned with removing spin-contamination from the wave 
 function \hugh{rather than improving the energy.
 It is well-known that the spin-projection needed to remove spin-contamination can require non-linear combinations