1. Description of a Chemical System as a Set of m Fixed Nuclei and n Electrons.- 1.1 Introduction.- 1.2 The SCF-LCAO-MO Approximation.- 1.3 The Correlation Energy Correction.- 1.4 Statistical Estimate of the Correlation Energy.- 1.5 Configuration Interaction.- 1.6 Combination of Statistical Methods and C.I. Techniques.- 1.7 Molecular Extra Correlation Energy.- 1.8 Choice of the Basis Set for the SCF-LCAO-MO Functions.- 1.9 Electron Population Analyses.- 1.10 Bond Energy Analyses in a Single Molecule.- 1.11 Bond Energy Analyses for Molecular Complexes.- 1.12 Bond Energy Analyses to Derive Chemical Structural Formulas.- 1.13 References.- 2. Structure of Liquid Water as a Test Case.- 2.1 Introduction.- 2.2 Approximate Hartree-Fock Potential for the Water Dimer.- 2.3 Polymers of Water Molecules in the Hartree-Fock Approximation.- 2.4 Monte Carlo Simulation of Liquid Water Using an Hartree-Fock Potential.- 2.5 Structure of Liquid Water Using an Accurate Potential.- 2.6 References.- 3. Coordination Numbers and Solvation Shells.- 3.1 Introduction.- 3.2 Structure of Water Arounds Ion Pairs.- 3.3 The Three-body Effects.- 3.4 More Accurate Determination of the Coordination Numbers for Ions.- 3.5 Solvation Potentials for Amino Acids.- 3.6 Conclusions.- 3.7 References.