Added Mayer GHF reference

Manuscript/EPAWTFT.tex

@@ -377,7 +377,7 @@ We will demonstrate how the choice of reference Hamiltonian controls the positio
 ultimately determines the convergence properties of the perturbation series.
 
 
-\titou{Practically, to locate EPs in a more complicated systems, one must solve simultaneously the following equations: \cite{Cejnar_2007}
+\titou{Practically, to locate EPs in a more complicated systems, one must solve simultaneously the following equations:\cite{Cejnar_2007}
 \begin{subequations}
 \begin{align}
 	\label{eq:PolChar}
@@ -446,7 +446,7 @@ From hereon, $i$ and $j$ denote occupied orbitals, $a$ and $b$ denote unoccupied
 
 % BRIEF FLAVOURS OF HF
 In the most flexible variant of real HF theory (generalised HF) the one-electron orbitals can be complex-valued
-and contain a mixture of spin-up and spin-down components.
+and contain a mixture of spin-up and spin-down components.\cite{Mayer_1993}
 However, the application of HF with some level of constraint on the orbital structure is far more common.
 Forcing the spatial part of the orbitals to be the same for spin-up and spin-down electrons leads to restricted HF (RHF) theory, while allowing different for different spins leads to the so-called unrestricted HF (UHF) approach.
 The advantage of the UHF approximation is its ability to correctly describe strongly correlated systems,