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:

-\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

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 '19 at 9:43

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)

   = {} &{-}\frac{i}{\hbar}\biggl[\, \sum_{n\in
     & +U_0\sum_{n,m\in

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 '19 at 10:40
  • @egreg, fair, code and image updated
    – daleif
    Aug 23 '19 at 10:48

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