How to split a long equation in Latex?

Question

I have a pretty long equation with me. I want to split the equation when using Texmaker. Can some one find me a proper way to do this? Thanks in advance.

\begin{equation}
\mathcal{H}=\sum_{\vec{k}}\left(\epsilon_{s}C^{\dagger}_{\vec{k}s}C_{\vec{k}s}+\epsilon_{p} C^{\dagger}_{\vec{k}p}C_{\vec{k}p}\right)-\sum_{\vec{k}}\left(\left[2\,t_{ss}\left(\cos  k_{x}+\cosk_{y}\right)\right]C^{\dagger}_{\vec{k}s}C_{\vec{k}s}+\left[\sqrt{2}t_{sp}\left(\ sin k_{x}-i\,\sin k_{y}\right)\right]C^{\dagger}_{\vec{k}s}C_{\vec{k}p}+ \left[\sqrt{2}t_{sp}\left(\sin k_{x}+i\,\sin k_{y}\right)\right]C^{\dagger}_{\vec{k}p}C_{\vec{k}s}-\left[2\,t_{pp}\left(\cos k_{x}+\cos k_{y}\right)\right]C^{\dagger}_{\vec{k}p}C_{\vec{k}}\right)

\end{equation}

Answer 1

You could use a split environment inside the equation environment. Choose the line breaks at natural-looking points. Vertical alignment points are indicated by the & symbol. The second row is shifted to the right by \quad, and rows 3 through 5 are shifted to the right by \qquad\qquad.

Note that you can't use \left( and \right) across line breaks; use explicit sizing instructions instead. To assure that the four pairs of square brackets have the same size, I would again use explicit sizing instructions.

\documentclass{article}  
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{split}
\mathcal{H}
&=\phantom{-}\sum_{\vec{k}} \Bigl( \epsilon_{s}C^{\dagger}_{\vec{k}s}C_{\vec{k}s}+\epsilon_{p} C^{\dagger}_{\vec{k}p}C_{\vec{k}p}\Bigr)\\
&\quad-\smash[b]{\sum_{\vec{k}}} \Bigl(\bigl[2\,t_{ss}(\cos  k_{x}+\cos k_{y})\bigr]C^{\dagger}_{\vec{k}s}C_{\vec{k}s}\\
&\qquad\qquad+\bigl[\sqrt{2}t_{sp}(\sin k_{x}-i\,\sin k_{y})\bigr]C^{\dagger}_{\vec{k}s}C_{\vec{k}p}\\
&\qquad\qquad+ \bigl[\sqrt{2}t_{sp}(\sin k_{x}+i\,\sin k_{y})\bigr]C^{\dagger}_{\vec{k}p}C_{\vec{k}s}\\
&\qquad\qquad-\bigl[2\,t_{pp}(\cos k_{x}+\cos  k_{y})\bigr]C^{\dagger}_{\vec{k}p}C_{\vec{k}}\Bigr)
\end{split}
\end{equation} 
\end{document}