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\section{Quantum Chemistry}  These days, there is a need to the routine use of quantum Quantum  mechanics (QM) in all aspects of in silico is increasingly accessible and relevant to molecular modeling and \textit{in silico}  drug design \cite{Vivo_2011}. QM plays a key role to resolve different problems from scoring protein–ligand poses to calculate QM descriptors for QSAR model building. It can improve the accuracy of the description of the interactions between molecules versus classical models. By the extraordinary increase in computational facilities, development and use of sophisticated algorithms for calculating wave functions of macromolecular systems have been accelerated \cite{Merz_2010}. Herein, several open source packages for quantum chemical calculations are explained.