Nesting tikz nodes

Question

I want to put a tikz graph (a Feynman diagram using tikz-feynman) inside other tikz nodes, but it doesn't seem to work. A MWE is below. It has to be compiled with lualatex as I'm using graphs.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{graphs}
\usepackage[compat=1.1.0]{tikz-feynman}

\begin{document}
\tikzset{
  box/.pic={
    \feynmandiagram[inner,horizontal=a to d]{
      a -- [fermion] b -- [fermion] c -- [fermion] d -- [draw=none]
      e -- [fermion] f -- [fermion] g -- [fermion] h -- [draw=none] a,
      b -- [boson] g, c -- [boson] f,
    };
  }
}

\begin{tikzpicture}
  \graph [clockwise=4,radius=5em]{
    % a/{B}, b/{\tikz{\pic {box};}}, c/{C}, d/{f}  %% <-- what I want to do
    a/{B}, b/{box}, c/{C}, d/{f}
  };
  \graph {
    (a) -> {(b), (d)}, {(b), (d)} -> (c)
  };
\end{tikzpicture}

\end{document}

PS: I also found out tikz-feynman does not work with the standalone document class after I had wasted a few hours!

EDIT: Thanks to @TorbjørnT., the above issues is due to standalone, and is resolved by starting with \RequirePackage{luatex85}.

Answer 1

Nesting tikzpictures isn't something you can always count on working, and you're nesting three levels deep. \feynmandiagram starts a tikzpicture, \tikz is a shortform of \begin{tikzpicture} .. \end{tikzpicture}, and you're placing the first inside the second inside a third tikzpicture.

An alternative that does work is to use a savebox.

Note that you don't actually need \usepackage{tikz} \usetikzlibrary{graphs} as tikz-feynman loads both.

\RequirePackage{luatex85}
\documentclass{standalone}
\usepackage[compat=1.1.0]{tikz-feynman}
\newsavebox{\foo}
\savebox{\foo}{
\feynmandiagram[horizontal=a to d]{
      a -- [fermion] b -- [fermion] c -- [fermion] d -- [draw=none]
      e -- [fermion] f -- [fermion] g -- [fermion] h -- [draw=none] a,
      b -- [boson] g, c -- [boson] f,
    };}
\begin{document}

\begin{tikzpicture}
  \graph [clockwise=4,radius=10em]{
     a/{B}, b/\usebox{\foo}, c/{C}, d/{f} 
  };
  \graph {
    (a) -> {(b), (d)}, {(b), (d)} -> (c)
  };
\end{tikzpicture}
\end{document}