17

Often in physics, the symbol \sim is used as a unary operator to mean "approximately."

For example, one might say "the energy of these processes is $\sim 4$ eV." However, this looks awkward because \sim is a binary operator and the spacing is incorrect. How can one use \sim act as a unary operator?

11

Just define a new command for it:

\newcommand{\ca}{{\sim}}

I suggest also to use siunitx, if you have units of measure to typeset in your document: it ensures uniform setting.

\documentclass{article}
\newcommand{\ca}{{\sim}}

\usepackage{siunitx}
\sisetup{input-protect-tokens=\ca,input-symbols=\ca}

\begin{document}
\SI{\ca 4}{eV}

$\ca 4$\,eV
\end{document}

The input might seem more difficult, but it's surely rewarding.

enter image description here

If you load amssymb you can change the definition to

\usepackage{amssymb}
\newcommand{\ca}{{\thicksim}}

and the result would be

enter image description here

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