This book summarizes recent impressive improvements in the application of Quantum Mechanics, coupled with the significant increase in both speed and storage capabilities of modern computers, that allow to depict the energy and reactive properties of chemically complex materials through first principles and destroy the dogmatic assumption that the natural complexity cannot be modeled. It presents methods of Quantum Chemistry applied to various fields of geoscience. The book aims to convey to the audience, methods and procedures apt to obtain sound thermodynamic and thermo-physical data for earth’s materials under various aggregation states. The attention of this book focusses on the applicative aspects of the various procedures, with reference to the underlying theory.