SRGGW/Manuscript/MRGW.tex

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\documentclass[aip,jcp,reprint,noshowkeys,superscriptaddress,onecolumn]{revtex4-1}
\usepackage{graphicx,dcolumn,bm,xcolor,microtype,multirow,amscd,amsmath,amssymb,amsfonts,physics,longtable,wrapfig,txfonts,siunitx}
\usepackage[version=4]{mhchem}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{txfonts}
\usepackage[
colorlinks=true,
citecolor=blue,
breaklinks=true
]{hyperref}
\urlstyle{same}
\newcommand{\ie}{\textit{i.e.}}
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% coordinates
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\newcommand{\bx}{\boldsymbol{x}}
\newcommand{\dbr}{d\br}
\newcommand{\dbx}{d\bx}
% methods
\newcommand{\GW}{\text{$GW$}}
\newcommand{\evGW}{ev$GW$}
\newcommand{\qsGW}{qs$GW$}
\newcommand{\GOWO}{$G_0W_0$}
\newcommand{\Hxc}{\text{Hxc}}
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%
\newcommand{\Ne}{N}
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\newcommand{\Nocc}{O}
\newcommand{\Nvir}{V}
% operators
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% energies
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% orbital energies
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% Matrix elements
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% Matrices
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% orbitals, gaps, etc
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% addresses
\newcommand{\LCPQ}{Laboratoire de Chimie et Physique Quantiques (UMR 5626), Universit\'e de Toulouse, CNRS, UPS, France}
\begin{document}
\title{Undressing $GW$ one determinant at a time}
\author{Pierre-Fran\c{c}ois \surname{Loos}}
\email{loos@irsamc.ups-tlse.fr}
\affiliation{\LCPQ}
\begin{abstract}
Here comes the abstract.
%\bigskip
%\begin{center}
% \boxed{\includegraphics[width=0.5\linewidth]{TOC}}
%\end{center}
%\bigskip
\end{abstract}
\maketitle
%%%%%%%%%%%%%%%%%%%%%%
\section{Introduction}
%%%%%%%%%%%%%%%%%%%%%%
Here comes the introduction.
%%%%%%%%%%%%%%%%%
\section{Theory}
%%%%%%%%%%%%%%%%%
In the case of {\GOWO}, the quasiparticle equation reads
\begin{equation}
\label{eq:qp_eq}
\eps{p}{\HF} + \SigC{p}(\omega) - \omega = 0
\end{equation}
where $\eps{p}{\HF}$ is the HF one-electron energy of the spatial orbital $\MO{p}(\br)$ and the correlation part of the frequency-dependent self-energy is
\begin{equation}
\label{eq:SigC}
\SigC{p}(\omega)
= \sum_{im} \frac{2\ERI{pi}{m}^2}{\omega - \eps{i}{\HF} + \Om{m}{\RPA}}
+ \sum_{am} \frac{2\ERI{pa}{m}^2}{\omega - \eps{a}{\HF} - \Om{m}{\RPA}}
\end{equation}
where
\begin{equation}
\ERI{pq}{m} = \sum_{ia} \ERI{pq}{ia} X_{ia,m}^\RPA
\end{equation}
are the screened two-electron repulsion integrals where $\Om{m}{\RPA}$ and $\bX{m}{\RPA}$ are the $m$th RPA eigenvalue and eigenvector obtained by solving the following (linear) RPA eigenvalue system:
\begin{equation}
\bA{}{\RPA} \cdot \bX{m}{\RPA} = \Om{m}{\RPA} \bX{m}{\RPA}
\end{equation}
with
\begin{equation}
A_{ia,jb}^{\RPA} = (\eps{a}{\HF} - \eps{i}{\HF}) \delta_{ij} \delta_{ab} + \ERI{ia}{bj}
\end{equation}
and
\begin{equation}
\ERI{pq}{ia} = \iint \MO{p}(\br_1) \MO{q}(\br_1) \frac{1}{\abs{\br_1 - \br_2}} \MO{i}(\br_2) \MO{a}(\br_2) d\br_1 \dbr_2
\end{equation}
The spectral weight of the solution $\eps{p,s}{\GW}$ is given by
\begin{equation}
\label{eq:Z}
0 \le Z_{p,s} = \qty[ 1 - \eval{\pdv{\SigC{p}(\omega)}{\omega}}_{\omega = \eps{p,s}{\GW}} ]^{-1} \le 1
\end{equation}
with the following sum rules:
\begin{align}
\sum_{s} Z_{p,s} & = 1
&
\sum_{s} Z_{p,s} \eps{p,s}{\GW} & = \eps{p}{\HF}
\end{align}
As shown recently, the quasiparticle equation \eqref{eq:qp_eq} can be recast as a linear eigensystem with exactly the same solution:
\begin{equation}
\bH^{(p)} \cdot \bc{}{(p,s)} = \eps{p,s}{\GW} \bc{}{(p,s)}
\end{equation}
with
\begin{equation}
\label{eq:Hp}
\bH^{(p)} =
\begin{pmatrix}
\eps{p}{\HF} & \bV{p}{\text{2h1p}} & \bV{p}{\text{2p1h}}
\\
\T{(\bV{p}{\text{2h1p}})} & \bC{}{\text{2h1p}} & \bO
\\
\T{(\bV{p}{\text{2p1h}})} & \bO & \bC{}{\text{2p1h}}
\end{pmatrix}
\end{equation}
and where the expressions of the 2h1p and 2p1h blocks reads
\begin{align}
C^\text{2h1p}_{IJA,KCL} & = \qty[ \qty( \eps{I}{\HF} + \eps{J}{\HF} - \eps{A}{\HF}) \delta_{JL} \delta_{AC} - 2 \ERI{JA}{CL} ] \delta_{IK}
\\
C^\text{2p1h}_{IAB,KCD} & = \qty[ \qty( \eps{A}{\HF} + \eps{B}{\HF} - \eps{I}{\HF}) \delta_{IK} \delta_{AC} + 2 \ERI{AI}{KC} ] \delta_{BD}
\end{align}
with the following expressions for the coupling blocks:
\begin{align}
V^\text{2h1p}_{p,KLC} & = \sqrt{2} \ERI{pK}{CL}
&
V^\text{2p1h}_{p,KCD} & = \sqrt{2} \ERI{pD}{KC}
\end{align}
By solving the secular equation
\begin{equation}
\det[ \bH^{(p)} - \omega \bI ] = 0
\end{equation}
we recover the dynamical expression of the self-energy \eqref{eq:SigC}, \ie,
\begin{equation}
\SigC{p}(\omega)
= \bV{p}{\text{2h1p}} \cdot \qty(\omega \bI - \bC{}{\text{2h1p}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2h1p}})}
+ \bV{p}{\text{2p1h}} \cdot \qty(\omega \bI - \bC{}{\text{2p1h}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2p1h}})}
\end{equation}
with
\begin{equation}
\label{eq:Z_proj}
Z_{p,s} = \qty[ c_{1}^{(p,s)} ]^{2}
\end{equation}
In the presence of intruder states, it might be interesting to move additional electronic configurations in the reference space.
Let us label as $p$ the reference 1h ($p = i$) or 1p ($p = a$) determinant and $qia$ the additional 2h1p ($qia = ija$) or 2p1h ($qia = iab$)
\begin{equation}
\label{eq:Hp_qia}
\bH^{(p,qia)} =
\begin{pmatrix}
\eps{p}{\HF} & V_{p,qia} & \bV{p}{\text{2h1p}} & \bV{p}{\text{2p1h}}
\\
V_{qia,p} & C_{qia,qia} & \bC{qia}{\text{2h1p}} & \bC{qia}{\text{2p1h}}
\\
\T{(\bV{p}{\text{2h1p}})} & \T{(\bC{qia}{\text{2h1p}})} & \bC{}{\text{2h1p}} & \bO
\\
\T{(\bV{p}{\text{2p1h}})} & \T{(\bC{qia}{\text{2p1h}})} & \bO & \bC{}{\text{2p1h}}
\end{pmatrix}
\end{equation}
with new blocks defined as
\begin{gather}
V_{p,qia} = V_{qia,p} \sqrt{2} = \ERI{pq}{ia}
\\
C_{qia,qia} = \text{sgn}(\eps{q}{\HF} - \mu) \qty[ \qty(\eps{q}{\HF} + \eps{a}{\HF} - \eps{i}{\HF} ) + 2 \ERI{ia}{ia} ]
\\
C_{qia,KLC}^\text{2h1p} = - 2 \ERI{ia}{CL} \delta_{qK}
\\
C_{qia,KCD}^\text{2p1h} = + 2 \ERI{ia}{KC} \delta_{qD}
\end{gather}
Downfolding Eq.~\eqref{eq:Hp_qia} yields the following frequency-dependent self-energy
\begin{equation}
\label{eq:Hp}
\bSigC{p,qia}(\omega) =
\begin{pmatrix}
\eps{p}{\HF} + \SigC{p}(\omega) & V_{p,qia} + \SigC{p,qia}(\omega)
\\
V_{qia,p} + \SigC{qia,p}(\omega) & C_{qia,qia} + \SigC{qia}(\omega)
\\
\end{pmatrix}
\end{equation}
with
\begin{gather}
\SigC{p}(\omega)
= \bV{p}{\text{2h1p}} \cdot \qty(\omega \bI - \bC{}{\text{2h1p}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2h1p}})}
+ \bV{p}{\text{2p1h}} \cdot \qty(\omega \bI - \bC{}{\text{2p1h}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2p1h}})}
\\
\SigC{qia}(\omega)
= \bC{qia}{\text{2h1p}} \cdot \qty(\omega \bI - \bC{}{\text{2h1p}} )^{-1} \cdot \T{\qty(\bC{qia}{\text{2h1p}})}
+ \bC{qia}{\text{2p1h}} \cdot \qty(\omega \bI - \bC{}{\text{2p1h}} )^{-1} \cdot \T{\qty(\bC{qia}{\text{2p1h}})}
\\
\SigC{p,qia}(\omega)
= \bV{p}{\text{2h1p}} \cdot \qty(\omega \bI - \bC{}{\text{2h1p}} )^{-1} \cdot \T{\qty(\bC{qia}{\text{2h1p}})}
+ \bV{p}{\text{2p1h}} \cdot \qty(\omega \bI - \bC{}{\text{2p1h}} )^{-1} \cdot \T{\qty(\bC{qia}{\text{2p1h}})}
\\
\SigC{qia,p}(\omega)
= \bC{qia}{\text{2h1p}} \cdot \qty(\omega \bI - \bC{}{\text{2h1p}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2h1p}})}
+ \bC{qia}{\text{2p1h}} \cdot \qty(\omega \bI - \bC{}{\text{2p1h}} )^{-1} \cdot \T{\qty(\bV{p}{\text{2p1h}})}
\end{gather}
Of course, the present procedure can be generalized to any number of states.
%%%%%%%%%%%%%%%%%%%%%%
\section{Conclusion}
%%%%%%%%%%%%%%%%%%%%%%
Here comes the conclusion.
d
%%%%%%%%%%%%%%%%%%%%%%%%
\acknowledgements{
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement No.~863481).}
%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section*{Data availability statement}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
The data that supports the findings of this study are available within the article.% and its supplementary material.
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\bibliography{MRGW}
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\end{document}