The First Principle Computation Study Of New Iron-based Superconductor LaOFeAs

Since the discovery of superconductor,the research of superconductive material has potential economic value and widely applied areas because of its particular physical properties.Especially the discovery of high critical temperature copper-oxide superconductors set off the study of high critical temperature superconductor.However,so far,there is no one acknowledged theory to explain the mechanism of high critical temperature superconductor,and it has seriously hampered the development of superconducting technology.The new iron-based high critical temperature superconductor in February of 2008 has broadened the peoples' thinking. Up to now,its critical temperature has breakthrough 50K by doping the lanthanide or under pressure.In this paper,we use the CASTEP task which is based on Density Function Theory in Material Studio computation software to study the property of ground state of mother material LaOFeAs,discuss the band structure and density of states in detail. We find that LaOFeAs is bad magnetic metal;the dominant states at the Fermi level come from Fe 3d atomic states and partial As 4p atomic states,electronics and holes co-existence at the Fermi level.The conduction is strongly anisotropic,only happening on the Fe-As layers.We research the electronic structure of LaO_1-xF_xFeAs in different F doping concentration using Virtual Crystal Approximation;discuss the doping effect on iron-based superconductor crystal structure and superconductivity. Computation indicates that the F-doping make the structure more stable and decrease the density of states at Fermi level which is propitious to superconductivity because of eliminating the spin-polarized instability.We also find that F-doping at Oxygen site excitation O-2p atomic states as the charge layer which is similar to the copper-oxide superconductor.LaOFeAs contains magnetic element Fe which is very different from early ideas that magnetic will destroy the superconducting.The magnetic moment calculated by Density Functional Theory is larger than the experiment value.In this article,we use LDA + U method to deal with such a strong correlation system,with a focus to examine the electronic Coulomb interaction on the impact of LaOFeAs have been more in line with the experimental data.From the computation results,we give the causes of most of iron-based superconductor is electron doping,that is,the Coulomb interaction of d electrons inhibit hole-type charge carrier through the Fermi level,so that the electronic energy-band dispersion enhanced.Therefore,the actual materials should focus on the electronic-type doping.When U increases to 4.5eV the Fermi level costs a small pinnacle and pseudo gap,but even if the U then increased,there have not been able to detect the insulation state of LaOFeAs.The study of iron-based superconductor material has just started,we select two aspects to compute,for many new problems remains to be studied in depth.