\documentclass[12pt]{article}
\usepackage{amsmath,amssymb,amsfonts}
\begin{document}
Periodic structures are constructed by using semisimple Lie algebras. Then
these structures are generalized to ionic structures. Finally Madelung constant
of these structures are calculated by solving Poisson equation in the
fundamental domain of corresponding Lie algebras with Dirichlet boundary
conditions. The obtained results are consistent with data of the ionic crystals
with the same coordination numbers as our structures.
\end{document}