Book excerpt: Fundamental Physicochemical Properties of Germanene-related Materials: A Theoretical Perspective provides a comprehensive review of germanene-related materials to help users understand the essential properties of these compounds. The book covers various germanium complex states such as germanium oxides, germanium on Ag, germanium/silicon composites and germanium compounds. Diverse phenomena are clearly illustrated using the most outstanding candidates of the germanium/germanene-related material. Delicate simulations and analyses are thoroughly demonstrated under the first-principles method, being fully assisted by phenomenological models. Macroscopic phenomena in chemical systems, including their principles, practices and concepts of physics such as energy, structure, thermodynamics and quantum chemistry are fully covered. Germanium-based materials play critical roles in the basic and applied sciences, as clearly revealed in other group-IV and group-V condensed-matter systems. Their atomic configurations are suitable for creating the active chemical bonding among the identical and/or different nearest-neighboring atoms leading to diverse physical/chemical/material environments. - Provides a comprehensive review of germanene-related materials with a physicochemical and theoretical foundation that is useful for readers in understanding the essential properties of these compounds - Presents a unique theoretical framework under single and multi-hybridization theory - Contains significant combinations with phenomenological and experimental measurements - Focuses on the study of macroscopic phenomena in chemical systems in terms of their principles, practices and concepts of physics such as energy, structure, thermodynamics and quantum chemistry