The First Principles Calculate The Electronic Structure And Physical Property Of YBa₂Cu₃O_7-d

There is not a perfect theory to explain the high temperature superconducting mechanism until now in the high temperature superconductor. So it is very import to study electronic structure of the high temperature superconductor. The electronic structure and the distributed character of charge density study of the high temperature superconductor which use the atomic cluster method combining the density function theory based on the first principle maybe provide important auspice to the high temperature superconducting mechanism.The density function theory which is combined with the cluster model of crystal lattice calculates the electronic structure of superconductivity YBa₂Cu₃O_7-d and the O vacancy effect of it. That can help us to more understand the high temperature superconducting mechanism and character.Firstly, it is the study of the energy gap of YBa₂Cu₃O_7-d. Our calculation explicitly demonstrated that the superconducting critical temperature is 93K in YBa₂Cu₃O₇, the energy gaps reach minimum which is not zero at T_c. The transition points of energy gap are corresponding respectively for T_c, T^* and T⁰. Because the O vacancy only induces the concentration of carrier particles decrease, and the concentration of carrier particles affect the electronic structure in CuC>2 plane in the same time. So the calculated energy gap indicates that the superconducting critical transformation temperature decreases in YBa₂Cu₃O₇ maked O vacancy when the concentration of O decreases.The HOMO of YBa₂Cu₃O₇ and YBa₂Cu₃O_7-dare about —3.808ev and -4.896ev, respectively, they obviously indicate that the different exchange-association function of orbits between Cu3d and O2p in CuO₂ plane. The calculated curve of the ground state energy is consistent with the energy gap, and the changes of crystal lattice parameter in a range of 0.001A induce remarkable change of electronic structure.Secondly, it is the calculated study of the low temperature's physical property in YBa₂Cu₃O_7-d. Our calculation explicitly demonstrated that the calculated low temperature's specific heat and its coefficient of YBa₂Cu₃O₇ are consistent with the experimental, and approve the existent of the three transition points T_c, T^* and T⁰.Finally, it is the calculated study of the specific structure of YBa₂Cu₃O_7-d. The 3 dimension figures of HOMO in YBa₂Cu₃O₇ indicate that there are three different...