still unhappy with IVC and IVD
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@ -520,19 +520,26 @@ Collecting every second-order term in the flow equation and performing the block
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\label{eq:diffeqF2}
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\dv{\bF^{(2)}}{s} = \bF^{(0)}\bW^{(1)}\bW^{(1),\dagger} + \bW^{(1)}\bW^{(1),\dagger}\bF^{(0)} \\ - 2 \bW^{(1)}\bC^{(0)}\bW^{(1),\dagger},
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\end{multline}
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which can be solved by simple integration along with the initial condition $\bF^{(2)}=\bO$ to give
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which can be solved by simple integration along with the initial condition $\bF^{(2)}(0)=\bO$ to give
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\begin{multline}
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F_{pq}^{(2)}(s) = \sum_{r\nu} \frac{\Delta_{pr\nu}+ \Delta_{qr\nu}}{\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2} W_{p,r\nu} W^{\dagger}_{r\nu,q} \\
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\times \qty[1 - e^{-(\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2) s}].
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\end{multline}
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At $s=0$, the second-order correction vanishes while, for $s\to\infty$, it tends towards the following static limit
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At $s=0$, the second-order correction vanishes, hence giving
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\begin{equation}
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\lim_{s\to0} \widetilde{\bF}(s) = \bF^{(0)},
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\end{equation}
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while, for $s\to\infty$, it tends towards the following static limit
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\begin{equation}
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\label{eq:static_F2}
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F_{pq}^{(2)}(\infty) = \sum_{r\nu} \frac{\Delta_{pr\nu}+ \Delta_{qr\nu}}{\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2} W_{p,r\nu} W_{q,r\nu}.
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\lim_{s\to\infty} F_{pq}^{(2)}(s) = \sum_{r\nu} \frac{\Delta_{pr\nu}+ \Delta_{qr\nu}}{\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2} W_{p,r\nu} W_{q,r\nu}.
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\end{equation}
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Note that, in the limit $s\to\infty$, the dynamic part of the self-energy [see Eq.~\eqref{eq:srg_sigma}] tends to zero.
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\titou{Therefore, the SRG flow continuously kills the dynamic part $\widetilde{\bSig}(\omega; s)$ while creating a static correction $\widetilde{\bF}(s)$.}
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Note that, in the limit $s\to\infty$, the dynamic part of the self-energy [see Eq.~\eqref{eq:srg_sigma}] tends to zero, \ie,
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\begin{equation}
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\lim_{s\to\infty} \widetilde{\bSig}(\omega; s) = 0.
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\end{equation}
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Therefore, the SRG flow continuously kills the dynamic part $\widetilde{\bSig}(\omega; s)$ while creating a static correction $\widetilde{\bF}(s)$.
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This transformation is done gradually starting from the states that have the largest denominators in Eq.~\eqref{eq:static_F2}.
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%%% FIG 1 %%%
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@ -541,7 +548,7 @@ This transformation is done gradually starting from the states that have the lar
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\includegraphics[width=\linewidth]{fig1.pdf}
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\caption{
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Functional form of the qs$GW$ self-energy (left) for $\eta = 1$ and the SRG-qs$GW$ self-energy (right) for $s = 1/(2\eta^2)$.
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\label{fig:fig1}}
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\label{fig:plot}}
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\end{figure*}
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%%% %%% %%% %%%
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@ -550,14 +557,14 @@ This transformation is done gradually starting from the states that have the lar
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% ///////////////////////////%
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Because the $s\to\infty$ limit of Eq.~(\ref{eq:GW_renorm}) is purely static, it can be seen as a qs$GW$ calculation with an alternative static approximation than the usual one of Eq.~(\ref{eq:sym_qsgw}).
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Unfortunately, as we shall discuss further in Sec.~\ref{sec:results}, in the $s\to\infty$ limit self-consistently solving the renormalized quasi-particle equation is once again quite difficult, if not impossible.
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Unfortunately, as we shall discuss further in Sec.~\ref{sec:results}, in the $s\to\infty$ limit, self-consistently solving the renormalized quasi-particle equation is once again quite difficult, if not impossible.
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However, one can define a more flexible new static self-energy, which will be referred to as SRG-qs$GW$ in the following, by discarding the dynamic part in Eq.~(\ref{eq:GW_renorm}).
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This yields a $s$-dependent static self-energy which matrix elements read
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\begin{multline}
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\label{eq:SRG_qsGW}
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\Sigma_{pq}^{\text{SRG}}(s) = \sum_{r\nu} \frac{\Delta_{pr\nu}+ \Delta_{qr\nu}}{\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2} W_{p,r\nu} W_{q,r\nu} \\ \times \qty[(1 - e^{-(\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2) s} ],
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\Sigma_{pq}^{\text{SRG}}(s) = \sum_{r\nu} \frac{\Delta_{pr\nu}+ \Delta_{qr\nu}}{\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2} W_{p,r\nu} W_{q,r\nu} \\ \times \qty[1 - e^{-(\Delta_{pr\nu}^2 + \Delta_{qr\nu}^2) s} ],
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\end{multline}
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Note that the SRG static approximation is naturally Hermitian as opposed to the usual case [see Eq.~(\ref{eq:sym_qsGW})] where it is enforced by symmetrization.
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Note that the SRG static approximation is naturally Hermitian as opposed to the usual case [see Eq.~(\ref{eq:sym_qsGW})] where it is enforced by brute-force symmetrization.
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Another important difference is that the SRG regularizer is energy dependent while the imaginary shift is the same for every state.
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Yet, these approximations are closely related because for $\eta=0$ and $s\to\infty$ they share the same diagonal terms.
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@ -566,13 +573,13 @@ Similarly, in SRG-qs$GW$ one might need to decrease the value of $s$ to ensure c
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The fact that the $s\to\infty$ static limit does not always converge when used in a qs$GW$ calculation could have been predicted because in this limit even the intruder states have been included in $\tilde{\bF}$.
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Therefore, one should use a value of $s$ large enough to include almost every state but small enough to avoid intruder states.
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It is instructive to plot both regularizing functions, this is done in Fig.~\ant{???}.
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It is instructive to plot both regularizing functions, this is done in Fig.~\ref{fig:plot}.
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The surfaces correspond to a value of the regularizing parameter value of 1.
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The SRG surface is much smoother than its qs counterpart.
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In fact the SRG regularization has less work to do because for $\eta=0$ there is a single singularity at $x=y=0$.
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On the other hand the function $f_{\text{qs}}(x,y;0)$ is singular on two entire axis, $x=0$ and $y=0$.
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The smoothness of the SRG surface might induce a smoother convergence of SRG-qs$GW$ compared to qs$GW$.
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The convergence properties and the accuracy of both static approximations will be quantitatively gauged in the results section.
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The convergence properties and the accuracy of both static approximations will be quantitatively gauged in Sec.~\ref{sec:results}.
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To conclude this section, the case of discontinuities will be briefly discussed.
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Indeed, it has been previously mentioned that intruder states are responsible for both the poor convergence of qs$GW$ and discontinuities in physical quantities at the $\GOWO$ level.
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