Ab-initio Studies On The Electronic Structures And Optical Properties Of Ba₂Ti₂Fe₂As₄O And CaIr₂

We study the electronic structure of superconductors Ba2Ti2Fe2As4O and CaIr2 by using the first principle calculation method which is based on density functional theory. We also study that how will the spin orbital coupling impact on the electronic structure of Ba2Ti2Fe2As4O and CaIr2. Based on this, we discuss the optical properties of the superconductors Ba2Ti2Fe2As4O and CaIr2.From the discussion of the electronic structure, we can obtain the following conclusions:The 3d electrons of Ti and 3d electrons of Fe make a greater contribution to the density of states near the Fermi surface of Ba2Ti2Fe2As4O. The density of states near the Fermi surface of CaIr2 is mainly contributed by the 5d electrons of Ir. The optical properties of the Ba2Ti2Fe2As4O is anisotropic, we can see this from the optical conductivity spectra:the curve in x direction is not synchronized with the z direction. The are very different. The first inter-band absorption peak along x-axis appears in 2.6 eV, while z-axis occurs in 3 eV. Either in x-axis or in z-axis, the peak position of the reflection spectra is in agreement with the electron energy loss graph. When the coupling of spin orbital is considered, the energy band of the Ba2Ti2Fe2As4O is found to be split, while the density of states is only different in the low energy region, and there is very little change in the high energy region. It can be seen from the optical properties of CaIr2 that it has metal property. The crossover of optical conductivity from intra-band to inter-band occurs near 0.8 eV. With the increase of the incident light energy, the optical conductivity decreases. The absorption peak of plasma is near 1.5 eV. After considering the effect of spin-orbit coupling, the energy band of CaIr2 splits obviously, we can see from the density of states, the size and location change, but trend of the line is not disappearing.