Potential energy surface, Hartree- Fock molecular theory, properties of limiting Hartree-Fock models, theoretical models, and theoretical model chemistry, beyond the Hartree- Fock, The Gaussian Basis Sets, Selection of a theoretical model, Graphical models. Semi-empirical methods: General introduction to semi-empirical methods. Introduction to Density Functional Theory (DFT) methods: Hohenberg Kohn theorems. Kohn-Sham orbitals. Exchange correlation functional. Local density approximation. Computational Chemistry Calculations: Potential energy surface: stationary point, transition state or saddle point, geometry optimization. Comparison and applications of Ab initio, DFT, Semi-empirical, and Molecular mechanics methods