Barium titanate (BaTiO3) is a perovskite crystal structure and it is well known to have many potential applications in microelectronic industry due to its high capabilities to enhance the performance of the capacitors and other energy storage devices. BaTiO3 has been reported to have a wide band gap around 3.4 eV from previous experimental studies. In theoretical studies, the analysis of the band structure of perovskite type of materials still under investigation due to high disagreement with the experimental result. The objective of this research is to investigate the band gap of the tetragonal BaTiO3 calculated using generalized gradient approximation (GGA) and hybrid functional (HSE03) with various pseudopotential methods performed by CASTEP module. The calculation using GGA show underestimation of energy band gap. However, the band gap calculated using HSE03 approximation shows an agreement with the experimental

The single layer of ZnSe has been studied to understand the structure using density functional theory. The vibrational frequencies of several cluster of ZnSe have been calculated when the Kohn-Sham equation solved at the ground state energy. We have done the calculation for 34 models of ZnSe clusters but only the stable molecules will be discussed. The bond length, Fermi energy and binding energy of ZnSe clusters have been calculated. The experimental result of single layer of ZnSe shown by Nesheva et. al. using different thickness of layers until 1 mu m [1]. The Raman spectra of ZnSe shown several peak for different thickness. In this paper, we will show the comparison of our calculated result with the experimental Raman spectra to show the existent of cluster.

To understand the electron doping effect into the parent compound BaFe2As2, we have theoretically evaluated phase stability and electronic structure of low temperature nickel (Ni) doped Ba(Fe(1-x)N(i)x)(2)As-2 superconductor. The optimized Fmmm phase are calculated by first principles pseudopotential and plane wave calculations within generalized-gradient approximation (GGA) with Perdew-Perke-Ernzerhof (PBE) exchange correlation functional. Our results show that nonmagnetic (NM) and antiferromagnetic (AFM) state having anisotropic spin configuration in the band structure calculation. This finding shows that a clear gap is observed in the band structure upon optimally Ni doping in the NM state with a small indirect gap 43.68 meV is found in the direction of G-X points. A spin gap 47.8 meV is obtained when a spin polarized orbital calculation is introduced to the system. The hybridization of Fe/Ni-3d and As-4p in the density of states (DOS) results a metallic region near the Fermi level and flat bands exist below the level. We suggest the observation provides a crucial understanding in the superconductivity of the materials.

The electronic structures of 5-phase of solid oxygen (O-2)(4) are studied within the framework of density functional theory. The intriguing molecule has been known to have magnetic properties at room temperature by applying pressure. Nevertheless, until now there was no evidence of band structure studied in the anti-ferromagnetic behaviour of (O-2)(4). We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O-2)(4) could not be seen experimentally, and antiferromagnetic configuration of (O-2)(4) was seen at higher pressure of about 10 GPa. The antiferromagnetic state transforms into the superconducting state as the sample temperature decreases. The results can serve as a useful approximation in studying general features of the electronic structure. The (O-2)(4) clusters are reported in the Raman study, having significant absorption at 1516 cm(-1) below infrared region.

We study the band structure of antiferromagnetic A(x)Fe(2)Se(2) (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of A(x)Fe(2)Se(2) will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the A(x)Fe(2)Se(2) is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level.

Sodium intercalation in graphite (GIC-Na) was investigated by the first principle calculation. The structure of GIC-Na was calculated using density functional theory (DFT) with the aid of CASTEP module of Material Studio. The exchange correlation functional has been treat by local density approximation (LDA) and generalized gradient approximation (GGA). It was shown that, unlike potassium GIC and lithium GIC, the band gap of GIC-Na was not induced and has same value of band gap with bulk graphite.