How to place a curly brace to the right of several lines in an align environment?

Question

\documentclass[a4paper]{article}
\usepackage{derivative}
\begin{document}

\begin{align*}
    \{q_a,q_b\} &= 0 = \{p_a,p_b\} \\
    \{q_a,p_b\} &= \delta_{ab} \\
    \{q_a,F\} &= \pdv{F}{q_a}\\
    \{p_a,F\} &= -\pdv{F}{p_a}
\end{align*}

\end{document}

I want to add a curly bracket to the right of the two first lines :

I tried to use the mathtools package:

\documentclass[a4paper]{article}
\usepackage{derivative}
\usepackage{mathtools}
\begin{document}
\begin{align}
    \negthickspace
    \begin{rcases}
        {q_a,q_b} &= 0 = {p_a,p_b} \
        {q_a,p_b} &= \delta_{ab}
    \end{rcases} \
    {q_a,F} &= \pdv{F}{q_a}\
    {p_a,F} &= -\pdv{F}{p_a}
\end{align}
\end{document}

But the alignment is then messed up

How can I achieve that, maybe without the rcases environment ?

Answer 1

You can position a large } while hiding it from the alignment:

\documentclass[a4paper]{article}
\usepackage{mathtools,derivative}
\begin{document}
\begin{align}
    {q_a,q_b} &= 0 = {p_a,p_b} 
\quad\smash{\raisebox{-10pt}{$\mathrlap{\Biggr}}$}}\
    {q_a,p_b} &= \delta_{ab} \[2pt]
    {q_a,F} &= \pdv{F}{q_a}\
    {p_a,F} &= -\pdv{F}{p_a}
\end{align}
\end{document}

Answer 2

You can use nicematrix:

\documentclass[a4paper]{article}
\usepackage{derivative}
\usepackage{nicematrix}
\begin{document}
\begin{equation}
\setlength{\arraycolsep}{0pt}
\renewcommand{\arraystretch}{1.5}
\begin{NiceArray}{r >{{}}c<{{}} >{\displaystyle}l}
  {q_a,q_b} &=& 0 = {p_a,p_b} \
  {q_a,p_b} &=& \delta_{ab} \[1ex]
  {q_a,F}   &=& \pdv{F}{q_a}\[2ex]
  {p_a,F}   &=& -\pdv{F}{p_a}
\CodeAfter\SubMatrix.{1-3}{2-3}}
\end{NiceArray}
\end{equation}
\end{document}

Answer 3

with tikzmark and calligraphy

\documentclass[a4paper]{article}
\usepackage{amsmath}
\usepackage{derivative}
\usepackage{tikz}
\usetikzlibrary{decorations,calligraphy,tikzmark}
\begin{document}
\begin{align*}
    \{q_a,q_b\} &= 0 = \tikzmarknode{ne}{\{p_a,p_b\}} \\
    \{q_a,p_b\} &= \tikzmarknode{se}{\delta_{ab}} \\
    \{q_a,F\} &= \pdv{F}{q_a}\\
    \{p_a,F\} &= -\pdv{F}{p_a}
\end{align*}
\begin{tikzpicture}[remember picture,overlay]
\draw[decorate, decoration={calligraphic brace, amplitude=4pt, raise=4pt}, thick]
([yshift=2pt]ne.north east) -- ([yshift=-2pt]ne.north east |- se.south east);
\end{tikzpicture}
\end{document}