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I use the breqn package and its dmath environment for multi-line equations so that I can have brackets across multi-line equations - eg a \left[ on one line, and a matching \right] on the next.

By default, breqn aligns subsequent lines to the = sign in the first line. For example, using:

\begin{dmath}
-\frac{i}{\hbar}\Tr\left\{\hat{\psi}^\dagger_s(x_1)\hat{\psi}_s(x_2)\left[\hat{H},\hat{\rho}_t\right]\right\}=-\frac{i}{\hbar}\left[\sum_{n\in S}\left(\chi^*_{n,s}(x_1)\tilde{H}_a(x_2)\chi_{n,s}(x_2)-\chi_{n,s}(x_2)\tilde{H}_a(x_1)\chi^*_{n,s}(x_1)\right)+U_0\sum_{n,m\in S}\chi^*_{n,s}(x_1)\chi_{n,s}(x_2)\left(\left|\chi_{m,!s}(x_2)\right|^2-\left|\chi_{m,!s}(x_1)\right|^2\right)\right]dt
\end{dmath}

I obtain the following:

enter image description here

How can I stop automatic alignment to the equals sign? This seems like it should be a simple setting somewhere, but I looked at the documentation for breqn and can't see any such option.

I am aware there are amsmath environments in which I can do this, but they don't allow automatic connection of \left and \right across lines.

  • 1
    Don't use breqn and split manually. The sizes chosen by \left and \right are patently wrong. – egreg Aug 23 at 9:43
2

For a longer comment. I agree with egreg that those \left\right are excessive

The alignment is using the recommendations from https://www.ams.org/publications/authors/mit-2.pdf (some of which breqn is also attempting to use)

\documentclass[a4paper]{article}
\usepackage{mathtools}
\DeclareMathOperator\Tr{Tr}
\begin{document}
\begin{equation}
  \begin{aligned}
    \MoveEqLeft[3]
    -\frac{i}{\hbar}\Tr\bigl\{\hat{\psi}^\dagger_s(x_1)\hat{\psi}_s(x_2)[\hat{H},\hat{\rho}_t]\bigr\}
    \\
   = {} &{-}\frac{i}{\hbar}\biggl[\, \sum_{n\in
       S}\bigl(\chi^*_{n,s}(x_1)\tilde{H}_a(x_2)\chi_{n,s}(x_2)-\chi_{n,s}(x_2)\tilde{H}_a(x_1)\chi^*_{n,s}(x_1)\bigr)
     \\
     & +U_0\sum_{n,m\in
       S}\chi^*_{n,s}(x_1)\chi_{n,s}(x_2)\bigl(|\chi_{m,!s}(x_2)|^2-|\chi_{m,!s}(x_1)|^2\bigr)\biggr]dt
  \end{aligned}
\end{equation}
\end{document}

enter image description here

  • I recommend using \, between a fence and a summation sign when the limits reach the size of the \sum symbol. – egreg Aug 23 at 10:40
  • @egreg, fair, code and image updated – daleif Aug 23 at 10:48

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