# How can I adjust the size of the square brackets in the equation?

I am trying to write an equation that includes fractions and the power of fractions. Here is my equation.

    $$\label{eq:vlj} \si{\volt\of{LJ}}= \varepsilon\Bigl[{\left(\frac{r_\textsubscript{0}}{r}\right)}^{12}- {\left(\frac{r_\textsubscript{0}}{r}\right)}^{6}\Bigr]$$


And the output is:

And i don' t like the position of the subscripts and superscripts nor the size of brackets how can I change them to have nice looking form ? I' d like to have bigger brackets and the sub and superscripts should be covered by them.

and I am using the packages:

\usepackage{epstopdf}
\usepackage{cite}
\usepackage[utf8]{inputenc}
\usepackage{siunitx}
\usepackage{booktabs}
\usepackage{fixltx2e}
\usepackage[fleqn]{mathtools}

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The position of the superscripts is affected by the {} you have around the left-right (and also by the fact that you use left-right rather than \bigl...\bigr Since you are manually choosing the size of the [ then if you want them to be larger use (say) \biggl or \Biggl instead. (Please always post complete documents showing all packages used (I don't recognise textsubscript for example) – David Carlisle Jan 18 '13 at 12:23
@DavidCarlisle -- actually, the size of the subscript 0 (forced by \textsubscript) is what makes the parentheses, and therefore the outer brackets, look too small, because it raises the rs in the numerators. although slightly larger brackets wouldn't be inappropriate, the brackets shown wouldn't look nearly so bad if it weren't for that "high" r in the numerators. – barbara beeton Jan 18 '13 at 13:18

Using \left[ and \right] would get you better outer brackets:

$$\label{eq:vlj} \varepsilon\left[\left(\frac{r_0}{r}\right)^{12}-\left(\frac{r_0}{r}\right)^{6}\right]$$


EDIT:

removed some unnecessary brackets and \textsubscript

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I'd remove the mysterious \textsubscript command: r_{0} is more than sufficient. And also the braces around \left...\right – egreg Jan 18 '13 at 12:27
@Timebandit thanks. Though I' d prefer the smaller size of subscripts. How is it possible ? – Yirmidokuz Jan 18 '13 at 12:47
@Yirmidokuz -- smaller (actually, normal sized for this environment) subscripts are produced by r_0 (or r_{0} as in the comment by egreg). \textsubscript forces a size that isn't appropriate here. in addition, the larger subscript forces the r to be higher than normal, causing the size of the parentheses to appear incorrect. – barbara beeton Jan 18 '13 at 13:12