Overview of Computational Chemistry the electronic structure theory

1 Overview of Computational Chemistry the electronic structure theory 

Based on the fundamental laws of physics [35], computational chemistry calculates properties, chemical structures and reactions numerically. Some methods can be used to model not only stable molecules, but also short-live, unstable intermediates and even transition states. In this way they can provide information about molecules and reactions which may be impossible to obtain through observation. The electronic structure theory (quantum mechanics) is considered as the most appropriate for calculating molecule properties, such as  

Quantum mechanics states that the energy and other related properties of a molecule may be obtained by solving the Schrbdinger equation  

Except for very simple systems, exact solutions to the Schrodinger equation are, however, only numerically feasible. Various mathematical approximations to its solution characterise the electronic structure methods. 

There are two major classes of electronic structure methods [36] Semi-empirical methods and 

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