\documentclass[12pt,a4paper]{article}
\textwidth16cm
\textheight24.7cm
\oddsidemargin0cm
\topmargin-0.5in
\pagestyle{empty}
\renewcommand{\baselinestretch}{1}
\usepackage{graphicx}
\begin{document}
\begin{center}
%%%%%%%%% ABSTRACT TITLE
{\large{\bf Abstract template and instructions for OPON 2020}}
%%%%%%%%% ABSTRACT AUTHORS
\vskip0.5\baselineskip{\bf First A. Author$^{1}$, Second B. Author$^{1,2}$, and Third C. Author${^2}$ }
%%%%%%%%% AFFILIATION
\vskip0.5\baselineskip{\em$^{1}$Institution1, Address1, City1, Country1 \\$^{2}$Institution2, Address2, City2, Country2 }
\end{center}
%%%%%%%%% ABSTRACT BODY
This template is a base for your abstract. You can extend it by using macros, packages, figures, automatic LaTeX references etc. However, please ensure to keep the margins of 25~mm on all sides, preferably use the standard 12~pt font, do not generate page numbers and do not exceed the one page length. We recommend formatting the references as below [1,2].  We would appreciate if the layout and formatting of this template is followed. The abstract book will be printed in black and white.

Please submit the abstract in a PDF file by email: opon2020@fuw.edu.pl

\begin{center}
\includegraphics[width=0.5\textwidth]{logo_opon2020.png}
\end{center}

\vskip\baselineskip\parindent0mm
{}[1] A. Authora, and B. Authorb, \textit{Phys. Rev. B} \textbf{89}, 568 (2012). \\
{}[2] C. Authorc, \textit{J. Lumin.} \textbf{97}, 312 (2015). \\

\end{document} 