SRGGW/Slides/SRG-GF.tex
2022-11-09 16:14:26 +01:00

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\documentclass[9pt,aspectratio=169]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{hyperref}
\usepackage{amsmath,amssymb,amsfonts,graphicx,xcolor,bm,microtype,wasysym,hyperref,tabularx,amscd,mhchem,physics}
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\newcommand{\bC}{\boldsymbol{C}}
\newcommand{\bF}{\boldsymbol{F}}
\newcommand{\bH}{\boldsymbol{H}}
\newcommand{\bHd}{\boldsymbol{H}_\text{d}}
\newcommand{\bHod}{\boldsymbol{H}_\text{od}}
\newcommand{\bO}{\boldsymbol{0}}
\newcommand{\bI}{\boldsymbol{1}}
\newcommand{\bV}{\boldsymbol{V}}
\newcommand{\bEta}{\boldsymbol{\eta}}
\newcommand{\bSig}{\boldsymbol{\Sigma}}
\newcommand{\bpsi}{\boldsymbol{\psi}}
\newcommand{\bPsi}{\boldsymbol{\Psi}}
\institute{Laboratoire de Chimie et Physique Quantiques, IRSAMC, UPS/CNRS, Toulouse \\
\url{https://lcpq.github.io/pterosor}}
\usetheme{pterosor}
\author{Antoine Marie \& Pierre-Fran\c{c}ois Loos}
\date{14th November 2022}
\title{Similarity Renormalization Group (SRG) Formalism Applied to Green's Function Methods}
\begin{document}
\maketitle
%-----------------------------------------------------
\begin{frame}{First-Quantized Form of SRG}
\begin{block}{General upfolded many-body perturbation theory (MBPT) problem}
\begin{align}
\qty[ \bF + \bSig(\omega) ] \bpsi = \omega \bpsi
& \qq{$\Leftrightarrow$}
\bH \bPsi = \omega \bPsi
\\
\bSig(\omega) = \bV \qty(\omega \bI - \bC)^{-1} \bV^{\dag}
& \qq{$\Leftrightarrow$}
\bH =
\begin{pmatrix}
\bF & \bV
\\
\bV^{\dagger} & \bC
\end{pmatrix}
\end{align}
\end{block}
%
\begin{block}{Perturbative partitioning}
\begin{equation}
\bH \equiv \bH(s=0) =
\underbrace{
\begin{pmatrix}
\bF & \bO
\\
\bO & \bC
\end{pmatrix}
}_{\bHd^{(0)}(s=0)}
+ \lambda
\underbrace{
\begin{pmatrix}
\bO & \bV
\\
\bV^{\dagger} & \bO
\end{pmatrix}
}_{\bHod^{(1)}(s=0)}
\qq{with}
\bHd^{(1)}(s=0) = \bHod^{(0)}(s=0) = \bO
\end{equation}
\end{block}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{Perturbative Expansions}
%
\begin{block}{Perturbative partitioning in the SRG framework}
\begin{equation}
\bH(s) =
\underbrace{
\begin{pmatrix}
\bF(s) & \bO
\\
\bO & \bC(s)
\end{pmatrix}
}_{\bHd{}(s)}
+ \lambda
\underbrace{
\begin{pmatrix}
\bO & \bV(s)
\\
\bV^{\dagger}(s) & \bO
\end{pmatrix}
}_{\bHod(s)}
\end{equation}
\end{block}
%
\begin{block}{Components of the Hamiltonian}
\begin{equation}
\bH(s) = \bH^{(0)}(s) + \lambda \bH^{(1)}(s) + \lambda^2 \bH^{(2)}(s) + \cdots
\end{equation}
\begin{equation}
\bC(s) = \bC^{(0)}(s) + \lambda \bC^{(1)}(s) + \lambda^2 \bC^{(2)}(s) + \cdots
\end{equation}
\begin{equation}
\bV(s) = \bV^{(0)}(s) + \lambda \bV^{(1)}(s) + \lambda^2 \bV^{(2)}(s) + \cdots
\end{equation}
\end{block}
\begin{block}{Wegner generator}
\begin{equation}
\bEta(s) = \bEta^{(0)}(s) + \lambda \bEta^{(1)}(s) + \lambda^2 \bEta^{(2)}(s) + \cdots
\end{equation}
\end{block}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{Zeroth-Order Terms}
\begin{block}{Wegner generator}
\begin{equation}
\bEta^{(0)}(s)
= \comm{\bHd^{(0)}(s)}{\bHod^{(0)}(s)}
= \bO
\end{equation}
\end{block}
%
\begin{block}{Zeroth-order Hamiltonian}
\begin{equation}
\dv{\bH^{(0)}(s)}{s}
= \comm{\bEta^{(0)}(s)}{\bH^{(0)}(s)}
= \bO
\qq{$\Rightarrow$}
\bH^{(0)}(s) = \bH^{(0)}{(s=0)}
\end{equation}
\end{block}
\alert{NB: we omit the $s$ dependency from hereon}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{First-Order Terms}
\begin{block}{Wegner generator}
\begin{equation}
\bEta^{(1)} = \comm{\bHd^{(0)}}{\bHod^{(1)}}
=
\begin{pmatrix}
\bO & \bF^{(0)} \bV^{(1)} - \bV^{(1)} \bC^{(0)}
\\
\bC^{(0)} \bV^{(1),\dagger} - \bV^{(1),\dagger} \bF^{(0)} & \bO
\end{pmatrix}
\end{equation}
\end{block}
%
\begin{block}{First-order Hamiltonian}
\begin{equation}
\dv{\bH^{(1)}}{s} = \comm{\bEta^{(1)}}{\bHd^{(0)}}
=
\begin{pmatrix}
\dv{\bF^{(1)}}{s} & \dv{\bV^{(1)}}{s}
\\
\dv{\bV^{(1),\dagger}}{s} & \dv{\bC^{(1)}}{s}
\end{pmatrix}
\end{equation}
with
\begin{gather}
\dv{\bF^{(1)}}{s}
= \dv{\bC^{(1)}}{s}
= \bO
\\
\dv{\bV^{(1)}}{s}
= 2 \bF^{(0)} \bV^{(1)} \bC^{(0)}
- \qty[\bF^{(0)}]^2 \bV^{(1)}
- \bV^{(1)} \qty[\bC^{(0)}]^2
\end{gather}
\end{block}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{Second-Order Terms}
\begin{block}{Wegner generator}
\begin{equation}
\bEta^{(2)}
= \comm{\bHd^{(0)}}{\bHod^{(2)}}
+ \underbrace{\comm{\bHd^{(1)}}{\bHod^{(1)}}}_{=\bO}
=
\begin{pmatrix}
\bO & \bF^{(0)} \bV^{(2)} - \bV^{(2)} \bC^{(0)}
\\
\bC^{(0)} \bV^{(2),\dagger} - \bV^{(2),\dagger} \bF^{(0)} & \bO
\end{pmatrix}
\end{equation}
\end{block}
%
\begin{block}{Second-order Hamiltonian}
\begin{equation}
\dv{\bH^{(2)}}{s} = \comm{\bEta^{(2)}}{\bHd^{(0)}} + \comm{\bEta^{(1)}}{\bHd^{(1)}}
=
\begin{pmatrix}
\dv{\bF^{(2)}}{s} & \dv{\bV^{(2)}}{s}
\\
\dv{\bV^{(2),\dagger}}{s} & \dv{\bC^{(2)}}{s}
\end{pmatrix}
\end{equation}
with
\begin{gather}
\dv{\bF^{(2)}}{s}
= \bF^{(0)} \bV^{(1)} \bV^{(1),\dag}
+ \bV^{(1)} \bV^{(1),\dag} \bF^{(0)}
- 2 \bV^{(1)} \bC^{(0)} \bV^{(1),\dag}
\\
\dv{\bC^{(2)}}{s}
= \bC^{(0)} \bV^{(1)} \bV^{(1),\dag}
+ \bV^{(1)} \bV^{(1),\dag} \bC^{(0)}
- 2 \bV^{(1)} \bF^{(0)} \bV^{(1),\dag}
\\
\dv{\bV^{(2)}}{s}
= 2 \bF^{(0)} \bV^{(2)} \bC^{(0)}
- \qty[\bF^{(0)}]^2 \bV^{(2)}
- \bV^{(2)} \qty[\bC^{(0)}]^2
\end{gather}
\end{block}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{Integration of the First-Order Terms}
\begin{equation}
\dv{\bF^{(1)}}{s} = \bO
\land
\bF^{(1)}(0) = \bO
\Rightarrow
\bF^{(1)}(s) = \bO
\end{equation}
\begin{equation}
\dv{\bC^{(1)}}{s}
\land
\bC^{(1)}(0) = \bO
\Rightarrow
\bC^{(1)}(s) = \bO
\end{equation}
\begin{equation}
\dv{\bV^{(1)}}{s}
= 2 \bF^{(0)} \bV^{(1)} \bC^{(0)}
- \qty[\bF^{(0)}]^2 \bV^{(1)}
- \bV^{(1)} \qty[\bC^{(0)}]^2
\land
\Rightarrow
\bV^{(1)}(s) = ?
\end{equation}
\end{frame}
%-----------------------------------------------------
%-----------------------------------------------------
\begin{frame}{Integration of the Second-Order Terms}
\begin{equation}
\dv{\bF^{(2)}}{s}
= \bF^{(0)} \bV^{(1)} \bV^{(1),\dag}
+ \bV^{(1)} \bV^{(1),\dag} \bF^{(0)}
- 2 \bV^{(1)} \bC^{(0)} \bV^{(1),\dag}
\land
\bF^{(2)}(0) = ?
\Rightarrow
\bF^{(2)}(s) = ?
\end{equation}
\begin{equation}
\dv{\bC^{(2)}}{s}
= \bC^{(0)} \bV^{(1)} \bV^{(1),\dag}
+ \bV^{(1)} \bV^{(1),\dag} \bC^{(0)}
- 2 \bV^{(1)} \bF^{(0)} \bV^{(1),\dag}
\land
\bC^{(2)}(0) = ?
\Rightarrow
\bC^{(2)}(s) = ?
\end{equation}
\begin{equation}
\dv{\bV^{(2)}}{s}
= 2 \bF^{(0)} \bV^{(2)} \bC^{(0)}
- \qty[\bF^{(0)}]^2 \bV^{(2)}
- \bV^{(2)} \qty[\bC^{(0)}]^2
\land
\Rightarrow
\bV^{(2)}(s) = ?
\end{equation}
\end{frame}
%-----------------------------------------------------
\end{document}