First Principle Investigation Of LaMnO₃and Its Catalytic Preformance

Along with the rapid development of computational methods and computertechnology, theory computation has become more and more important in modern science.Due to its moderate computational consume and high precision, density functional theory(DFT) has become one of the most important methods in condensed matter physics,computational chemistry and material science. Thus, in the field of chemical industry, thetheoretical calculation is to explore factors such as system of heterogeneous catalystactivity and achieve catalyst design, screening, synthesis, production process of scientific,systematic, and modeling, so that it makes people clearly realize the surface structure andproperties of materials from the atom and the electron level and guide the high selectivecatalyst design, it has opened up a new road for people to better understand the catalyticproblems in chemical engineering.In this paper, the bulk and the surface of LaMnO3have been investigated usingfirst-principles plane-wave pseudopotential method under the framework of densityfunctional theory. The main results were as follows:(1)The various magnetic structures of bulk LaMnO3was performed by the methodof spin-polarized calculation, main result as follows: The energy of LaMnO3differentmagnetic structures in order of size: NM>G-AFM>C-AFM>A-AFM>FM, i.e. The cubicLaMnO3has a stable ferromagnetic ground state; The various magnetic structures of bulkLaMnO3was performed by the method of spin-polarized calculation. There is no bandgap in the density of states of spin-up, and the spin-down band gap is2.2eV, respectively.The ferromagnetic LaMnO3is half-metallic, while others have a metallic magneticstructures. By using Mulliken method, we estimate the ionic configuration forperovskite LaMnO3(FM) in the fundamental state to be La+1.45Mn+0.72O-0.72.(2)The surface relaxation calculations of the different terminations of LaMnO3(001),(110) and (111) surfaces were carried out, the total energy is decreased, the differentatom is relaxed and the charge occurs also reallocation after surface relaxation. Throughthe calculation of surface energy, the (001) surfaces is lowest in the three low miller index surface, i.e. LaMnO3(001) plane is the most stable. The surface energy withvacancies is considerably lower than the defectless surface. In other words: theintroduction of surface vacancies into the defectless surface has a strong stabilizing effect.Charge redistribution results confirmed that macroscopic dipole moment of polarizationsurface can be cancelled in two ways by changing the surface electronic structure andsurface composition.(3)The adsorption of oxygen on the surface of LaMnO3(001) made a simplecalculation, the results show that: the LaMnO3(001) surface with oxygen vacancies hasquite high catalytic activity for O2. This is mainly due to the oxygen vacancy left twoelectrons on the surface, and molecule is an electron acceptor. O2molecules interact withthe oxygen vacancy, so as to make the defective surface has high activity for the O2molecules.In the calculation process, the different termination of the LaMnO3(001),(110) and(111) surface was selected as the research object. The atomic and electronic structures ofLaMnO3body and a variety of surface have been researched by using quantummechanics software CASTEP, so as to reveal the material structure, properties and therelationship between the two.