OK with Sec IV and V
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@ -22,7 +22,7 @@ This contribution has never been submitted in total nor in parts to any other jo
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In the present contribution, we apply the similarity renormalization group (SRG) approach to the well-known $GW$ approximation of many-body perturbation theory.
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We show that the SRG transformation allows us to derive, from first principles, a new static and hermitian expression for the self-energy that can be directly employed in self-consistent $GW$ calculations.
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As shown on a large set of molecules, the resulting SRG-based regularized self-energy significantly accelerates the convergence of $GW$ calculations and slightly improves the overall accuracy.
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As shown on a large set of molecules, the resulting SRG-based regularized self-energy significantly accelerates the convergence of $GW$ calculations and improves the overall accuracy.
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We hope that these new technical developments will broaden the applicability of Green’s function methods in the molecular electronic structure community and beyond.
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Because of the novelty of this work and its potential impact in quantum chemistry and condensed matter physics, we expect it to be of interest to a wide audience within the chemistry and physics communities.
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@ -1,7 +1,7 @@
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%% This BibTeX bibliography file was created using BibDesk.
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%% http://bibdesk.sourceforge.net/
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%% Created for Pierre-Francois Loos at 2023-03-10 09:19:55 +0100
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%% Created for Pierre-Francois Loos at 2023-03-10 11:18:15 +0100
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%% Saved with string encoding Unicode (UTF-8)
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@ -307,11 +307,10 @@
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@inbook{Bickers_2004,
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abstract = {Self-consistent field techniques for the many-electron problem are examined using the modern formalism of functional methods. Baym-Kadanoff, or $\Phi$-derivable, approximations are introduced first. After a brief review of functional integration results, the connection between conventional mean-field theory and higher-order Baym-Kadanoff approximations is established through the concept of the action functional. The $\Phi$-derivability criterion for thermodynamic consistency is discussed, along with the calculation of free-energy derivatives. Parquet, or crossing-symmetric, approximations are introduced next. The principal advantages of the parquet approach and its relationship to Baym-Kadanoff theory are outlined. A linear eigenvalue equation is derived to study instabilities of the electronic normal state within Baym-Kadanoff or parquet theory. Finally, numerical techniques for the solution of self-consistent field approximations are reviewed, with particular emphasis on renormalization group methods for frequency and momentum space.},
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address = {New York, NY},
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author = {Bickers, N. E.},
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booktitle = {Theoretical Methods for Strongly Correlated Electrons},
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date-added = {2023-01-30 14:19:12 +0100},
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date-modified = {2023-01-30 14:19:12 +0100},
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date-modified = {2023-03-10 11:18:04 +0100},
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doi = {10.1007/0-387-21717-7_6},
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editor = {S{\'e}n{\'e}chal, David and Tremblay, Andr{\'e}-Marie and Bourbonnais, Claude},
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isbn = {978-0-387-21717-8},
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@ -15327,11 +15326,12 @@
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@article{Lee_2018a,
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author = {J. Lee and M. Head-Gordon},
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date-added = {2018-09-01 12:02:40 +0200},
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date-modified = {2020-12-09 09:44:44 +0100},
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date-modified = {2023-03-10 11:16:08 +0100},
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doi = {10.1021/acs.jctc.8b00731},
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journal = {J. Chem. Theory Comput.},
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pages = {ASAP article},
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pages = {5203--5219},
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title = {Regularized Orbital-Optimized Second-Order M{\o}ller--Plesset Perturbation Theory: A Reliable Fifth-Order-Scaling Electron Correlation Model with Orbital Energy Dependent Regularizers},
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volume = {14},
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year = {2018},
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bdsk-url-1 = {https://doi.org/10.1021/acs.jctc.8b00731}}
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@ -1,5 +1,5 @@
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\documentclass[aip,jcp,reprint,noshowkeys,superscriptaddress]{revtex4-1}
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\usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,longtable,wrapfig,bbold,siunitx,xspace,ulem}
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\usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,longtable,wrapfig,bbold,siunitx,xspace}
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\usepackage[version=4]{mhchem}
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\usepackage[utf8]{inputenc}
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@ -232,7 +232,7 @@ These solutions can be characterized by their spectral weight given by the renor
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The solution with the largest weight $Z_p \equiv Z_{p,z=0}$ is referred to as the quasiparticle while the others are known as satellites (or shake-up transitions).
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However, in some cases, Eq.~\eqref{eq:G0W0} can have two (or more) solutions with similar weights, hence the quasiparticle is not well-defined.
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One obvious drawback of the one-shot scheme mentioned above is its starting point dependence.
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One obvious drawback of the one-shot scheme mentioned above is its starting-point dependence.
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Indeed, in Eq.~\eqref{eq:G0W0} we choose to rely on HF orbital energies but this is arbitrary and one could have chosen Kohn-Sham energies (and orbitals) instead.
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As commonly done, one can even ``tune'' the starting point to obtain the best possible one-shot $GW$ quasiparticle energies. \cite{Korzdorfer_2012,Marom_2012,Bruneval_2013,Gallandi_2015,Caruso_2016,Gallandi_2016}
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@ -290,8 +290,8 @@ This transformation can be performed continuously via a unitary matrix $\bU(s)$,
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\label{eq:SRG_Ham}
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\bH(s) = \bU(s) \, \bH \, \bU^\dag(s),
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\end{equation}
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\ant{where the flow parameter $s$ controls the extent of the decoupling and is related to an energy cutoff $\Lambda=s^{-1/2}$.
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For a given value of $s$, only states with energy denominators smaller than $1/\Lambda$ will be decoupled from the reference space, hence avoiding potential intruders.}
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where the flow parameter $s$ controls the extent of the decoupling and is related to an energy cutoff $\Lambda=s^{-1/2}$.
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For a given value of $s$, only states with energy difference (with respect to the reference space) greater than $\Lambda$ are decoupled from the reference space, hence avoiding potential intruders.
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By definition, the boundary conditions are $\bH(s=0) = \bH$ [or $\bU(s=0) = \bI$] and $\bH^\text{od}(s=\infty) = \bO$.
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An evolution equation for $\bH(s)$ can be easily obtained by differentiating Eq.~\eqref{eq:SRG_Ham} with respect to $s$, yielding the flow equation
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@ -518,11 +518,11 @@ The second-order renormalized quasiparticle equation is given by
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% \qty[ \widetilde{\bF}(s) + \widetilde{\bSig}(\omega; s) ] \bX = \omega \bX,
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\qty[ \widetilde{\bF}(s) + \widetilde{\bSig}(\omega = \epsilon_p; s) ] \psi_p(\bx) = \epsilon_p \psi_p(\bx),
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\end{equation}
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with a regularized Fock matrix of the form
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with a renormalized Fock matrix of the form
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\begin{equation}
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\widetilde{\bF}(s) = \bF^{(0)}+\bF^{(2)}(s),
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\end{equation}
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and a regularized dynamical self-energy
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and a renormalized dynamical self-energy
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\begin{equation}
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\label{eq:srg_sigma}
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\widetilde{\bSig}(\omega; s) = \bV^{(1)}(s) \left(\omega \bI - \bC^{(0)}\right)^{-1} (\bV^{(1)}(s))^{\dagger},
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@ -570,14 +570,14 @@ For $s\to\infty$, it tends towards the following static limit
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\label{eq:static_F2}
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\lim_{s\to\infty} \widetilde{\bF}(s)
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= \epsilon_p \delta_{pq}
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+ \sum_{r\nu} \frac{\Delta_{pr}^{\nu}+ \Delta_{qr}^{\nu}}{(\Delta_{pr}^{\nu})^2 + (\Delta_{qr}^{\nu})^2} W_{pr}^{\nu} W_{qr}^{\nu}.
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+ \sum_{r\nu} \frac{\Delta_{pr}^{\nu}+ \Delta_{qr}^{\nu}}{(\Delta_{pr}^{\nu})^2 + (\Delta_{qr}^{\nu})^2} W_{pr}^{\nu} W_{qr}^{\nu},
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\end{equation}
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while 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) = \bO.
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\end{equation}
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Therefore, the SRG flow continuously transforms the dynamical self-energy $\widetilde{\bSig}(\omega; s)$ into a static correction $\widetilde{\bF}^{(2)}(s)$.
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As illustrated in Fig.~\ref{fig:flow} (magenta curve), this transformation is done gradually starting from the states that have \ant{the largest denominators} in Eq.~\eqref{eq:static_F2}.
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As illustrated in Fig.~\ref{fig:flow} (magenta curve), this transformation is done gradually starting from the states that have the largest denominators in Eq.~\eqref{eq:static_F2}.
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For a fixed value of the energy cutoff $\Lambda$, if $\abs*{\Delta_{pr}^{\nu}} \gg \Lambda$, then $W_{pr}^{\nu} e^{-(\Delta_{pr}^{\nu})^2 s} \approx 0$, meaning that the state is decoupled from the 1h and 1p configurations, while, for $\abs*{\Delta_{pr}^{\nu}} \ll \Lambda$, we have $W_{pr}^{\nu}(s) \approx W_{pr}^{\nu}$, that is, the state remains coupled.
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@ -615,7 +615,7 @@ Indeed, the fact that SRG-qs$GW$ calculations do not always converge in the larg
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Therefore, one should use a value of $s$ large enough to include as many states as possible but small enough to avoid intruder states.
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It is instructive to examine the functional form of both regularizing functions (see Fig.~\ref{fig:plot}).
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These have been plotted for a regularizing parameter value of $\eta=1$, where we have set $s=1/2\eta^2$ such that the first-order Taylor expansion around $(x,y) = (0,0)$ of both functional forms is equal.
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These have been plotted for a regularizing parameter value of $\eta=1$, where we have set $s=1/(2\eta^2)$ such that the first-order Taylor expansion around $(x,y) = (0,0)$ of both functional forms is equal.
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One can observe that the SRG-qs$GW$ surface is much smoother than its qs$GW$ counterpart.
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This is due to the fact that the SRG-qs$GW$ functional at $\eta=0$, $f^{\SRGqsGW}(x,y;0)$, has fewer irregularities.
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In fact, there is a single singularity at $x=y=0$.
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@ -656,9 +656,9 @@ However, in order to perform black-box comparisons, these parameters have been f
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The $\eta$ value has been set to \num{e-3} for the conventional $G_0W_0$ calculations (where we eschew linearizing the quasiparticle equation) while, for the qs$GW$ calculations, $\eta$ has been chosen as the largest value where one successfully converges the 50 systems composing the test set.
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The various $GW$-based sets of values are compared with a set of reference values computed at the $\Delta$CCSD(T) level with the same basis set.
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The $\Delta$CCSD(T) principal ionization potentials (IPs) and electron affinities (EAs) have been obtained using \textsc{gaussian 16} \cite{g16} with default parameters within the restricted and unrestricted HF formalism for the neutral and charged species, respectively.
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The $\Delta$CCSD(T) principal ionization potentials (IPs) and electron affinities (EAs) have been obtained using \textsc{gaussian 16} \cite{g16} (with default parameters) within the restricted and unrestricted formalism for the neutral and charged species, respectively.
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The numerical data associated with this study are reported in the {\SupInf}.
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All the numerical data associated with this study are reported in the {\SupInf}.
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%=================================================================%
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\section{Results}
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