# How to create a math environment with one row on one side, and two on the other?

I have the following math equations:

\begin{align*}
&\mathcal{H} = \mathcal{H}^{(0)} + \mathcal{H}^{(1)} \\
&\mathcal{H}^{(0)} = -\frac{\hbar^2}{2m}(\nabla_{1}^{2} + \nabla_{2}^{2}) - \frac{e^2}{r_1} - \frac{e^2}{r_2}\\
&\mathcal{H}^{(1)} = \left(\frac{e^2}{R_{ab}} + \frac{e^2}{r_{12}} - \frac{e^2}{r_{a1}} - \frac{e^2}{r_{b2}}\right)
\end{align*}


I would like to have the first equation vertically centred on the left, drop the where, and simply have the other two on the right side in two different rows. How can this be achieved?

I've tried using tables, but this requires tabu or arrays. Source

I would like an amsmath only solution, but if this isn't possible then anything that isn't floating would be great.

From the comment to Werner's solution I understand, that you want even easier to obtain variant:

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\mathcal{H} = \mathcal{H}^{(0)} + \mathcal{H}^{(1)} \qquad \begin{aligned} &\mathcal{H}^{(0)} = -\frac{\hbar^2}{2m}(\nabla_{1}^{2} + \nabla_{2}^{2}) - \frac{e^2}{r_1} - \frac{e^2}{r_2}\\ &\mathcal{H}^{(1)} = \left(\frac{e^2}{R_{ab}} + \frac{e^2}{r_{12}} - \frac{e^2}{r_{a1}} - \frac{e^2}{r_{b2}}\right) \end{aligned}

\end{document} With a different alignment, you can also use this:

\documentclass[11pt, a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}

\begin{document}

\begin{align*}
\mathcal{H} &= \mathcal{H}^{(0)} + \mathcal{H}^{(1)}
&\mathcal{H}^{(0)}& = -\frac{\hbar^2}{2m}(\nabla_{1}^{2} + \nabla_{2}^{2}) - \frac {e^2} {r_1} - \frac{e^2}{r_2}\\
& &  \mathcal{H}^{(1)} &= \left(\frac{e^2}{R_{ab}} + \frac{e^2}{r_{12}} - \frac{e^2} {r_{a1}} - \frac{e^2}{r_{b2}}\right)
\end{align*}

\end{document} • Unrelated, but you should adjust your font package to use lining figures in math mode rather than old style figures. Old style figures are meant to typeset e.g. years inside of a paragraph. – Henri Menke Dec 14 '13 at 13:10
• Oh ! For the example, I actually used the MinionPro package (not mentioned in the source-code as it is irrelevant) with the same options as for my personal use. I usually prefer (personal taste) to have old style numbers for coefficients, and lining numbers for exponent and indices. It often was so in old french maths books. I'll take care of that next time. – Bernard Dec 14 '13 at 19:43