\documentclass[aps,pr,onecolumn,superscriptaddress,noshowpacs,a4paper,15pt]{revtex4}
\pdfoutput=1
\bibliographystyle{apsrev4}
\usepackage{color}
\usepackage{dcolumn} %Align table columns on decimal point
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{graphicx}
\usepackage[pdftex]{hyperref}
\hypersetup{colorlinks=true,citecolor=blue,linkcolor=red,urlcolor=blue}
\usepackage[all]{hypcap}
\newcommand{\red}{\color{red}}
\newcommand{\blue}{\color{blue}}
\definecolor{green}{rgb}{0,0.5,0}
\newcommand{\green}{\color{green}}
\newcommand{\white}{\color{white}}
%\newcommand{\cite}[1]{\hspace{-1 ex} % \nocite{#1}\citenum{#1}}
\thickmuskip=0.5\thickmuskip %shorter spaces in math

\begin{document}

\begingroup
\Large
\begin{eqnarray*}
  E & = & \frac{1}{2} \sum_i \sum_{j \neq i} V_{ij} \\[15pt]
  V_{ij} & = & e^{-\lambda (r_{ij} -z_0)} \left [ C + f(\rho_{ij}) + f(\rho_{ji}) - A \left ( \frac{r_{ij}}{z_0}\right )^{-6} \right ] \\
  \rho_{ij}^2 & = & r_{ij}^2 - ({\bf r}_{ij}\cdot {\bf n}_{i})^2 \\[15pt]
  \rho_{ji}^2 & = & r_{ij}^2 - ({\bf r}_{ij}\cdot  {\bf n}_{j})^2 \\[15pt]
  f(\rho) & = &  e^{-(\rho/\delta)^2} \sum_{n=0}^2 C_{2n} { (\rho/\delta) }^{2n}
\end{eqnarray*}
\endgroup
\end{document}
