First-principles Study Of Gas Adsorption On Low Dimensional Materials

The exotic features in optical, electrical, mechanical and other physical and chem-ical properties of low dimensional materials attract many physicists, chemists and ma-terials scientists’interests. Graphene is the hottest star in material science. Germanium and carbon belong to the same family. Recently, Germanium monolayer similar to graphene, also known as germanene is confirmed theoretically and then successfully synthesized in experiment. It may become the latest popular low dimensional material.With the rapid development of computer science and technology in the past decades, theoretical basis of the first-principles calculations based on density functional theory and numerical calculation algorithm has made a significant research progress and be-come one of the most useful tools in explaining the materials’properties and designing devices. In this article, we mainly use first-principles calculation method to study the electronic structure and the gas adsorption behavior on germanene.The dissertation contains three chapters. In the first part, we mainly present the ba-sic theoretical framework of the first principles calculations and some common used ap-proximate methods. We first introduce two basic approximations, Born-Oppenheimer and Hartree-Fock approximations. Then we introduce the core of the density functional theory, the Hohenberg-Kohn equation. We also present some common used exchange-correlation functional including LDA, GGA, hybrid functional, et al. At last, we in-troduce some common used DFT calculation tools such as VASP, Materials Studio, SIESTA, Quantum-Espresso and WIEN2k.In the second part, we begin to introduce the basic concepts of graphene and then give a brief description of other low dimensional materials, h-BN, transition metal dichalcogenides(TMD) and phosphorene. Many ways were used to functionalize these materials to expand their practical uses and gas adsorption is one of them. The ad-sorption of small molecules, aromatic and non-aromatic molecules was found to create marked effects in modifying electronic structure and other properties. At last, we sum-marize some practical use of them.In the third part, we systematically study the adsorption behavior of some common gas. These gas molecule show various behaviors on germanene. CO, N2, H2O, CO2are adsorbed on germanene physically, while NH3, NO and O2are chemically adsorbed. The marked modification in the electronic and magnetic properties of germanene in-duced by the molecules like NO2and NO together with a moderate binding energy, suggests that germanene is promising for molecular sensor applications. The easily dissociation of O2provides a feasible way to chemically functionalize germanene.