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 result. � 2017 Author(s).

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?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. � 2014 AIP Publishing LLC.

Luminescence is emission of light by a substance not resulting from heat. It is form of cold body radiation. It can be caused by chemical reactions of the substance with other substances around it, electrical energy, subatomic motions or stress on a crystal. There are many types of luminescence. One of it is phosphorescent. Phosphorescent is made from phosphors such as doped strontium aluminate. Phosphorescent emission light persists long after it has been exposed to light and will fading over time. Promethium (Pm) is low energy beta emitter. It does not degrade the phosphor lattice and the luminosity of the material does not degrade so fast. Promethium based paints are safer than Radium (Ra) and have half-life about more than two years. Promethium usually found in form oxidation called promethium (III) oxide (Pm2O3) and usually applied on watch and phones dial. The study of a band structure of Pm2O3 has not been covered yet. By using density functional theory, we calculated the band gap of promethium (III) oxide from it crystalline structure. The calculated band structure show a clear band gap between valence and conduction band at Fermi level. However the value shows very small gap at 0.286 eV. The density of state and partial density of states has been produced. The calculation has been done using different type of approximation from general gradient approximation (GGA).

We studied the clusters of GaAs by using the density functional theory simulation to optimize the structure. We determined the binding energy, bond lengths, Fermi energy and vibrational frequencies for all of the clusters. We use the Raman data of nanowires of GaAs to compare our calculated values with the experimental values of the vibrational frequencies. The nanowire of GaAs gives a Raman line at 256 cm-1 whereas in the bipyramidal Ga 2As3 the calculated value is 256.33 cm-1. Similarly 285 cm-1 found in the experimental Raman data agrees with 286.21 cm-1 found in the values calculated for Ga2As 2 (linear) showing that linear bonds occur in the nanowire. The GaAs is found in two structures zinc-blend as well as wurtzite structures. In the nanowire mixed structures as well as clusters are formed.

The nanometer size clusters are often present in ZnO. We have calculated the vibrational frequencies of zinc oxide by using the density-functional theory. We synthesized clusters of ZnO starting with ZnOn and continue with Zn2On, Zn3On and Zn4On with n = 1, 2, 3 and 4. By minimizing the energy of the Schr�dinger equation, we found the bond lengths and the vibrational frequencies of each cluster. These calculated data are compared to the experimentally measured Raman spectra of ZnO4 to identify the clusters which exist in this material. The density-functional theory in the local density approximation (LDA) is used with double numerical basis set. From this calculation, we find that the bond length for the cluster of ZnO 4 with tetrahedral symmetry (Td) is 1.923 � and the vibrational frequencies are 94.4 cm-1 and 440.4 cm-1 with degeneracy of 3 each. We have made several clusters using zinc and oxygen atoms and have calculated the vibrational frequencies, degeneracies and intensities in each case.

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(Fe1-xNix)2As2 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. � 2016 Author(s).

The electronic structures of "-phase of solid oxygen (O2)4 are studied within the framework of densityfunctional 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 antiferromagnetic behaviour of (O2)4. We report a comparison study for spin and non-spin polarization orbital which suggests that this ferromagnetic configuration of (O2)4 could not be seen experimentally, and antiferromagnetic configuration of (O2)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 (O2)4 clusters are reported in the Raman study, having significant absorption at 1516 cm-1 below infrared region.

Theoretical molecular dynamic simulations based on plane-wave and pseudopotential density functional theory (DFT) calculations with CASTEP code were employed to explore the pressure influence on the properties of silicon carbide polytypes. The changes in the lattice and electronic structures of 2H-, 4H-, and 6H-SiC polytypes at room temperature were investigated when pressures from 10 GPa to 200 GPa were applied. It�s found that the applied pressures didn�t cause a change in the hexagonal structure of the crystals. However, the structural and electronic properties clearly affected by the compression. The dependence of volume reduction (V/Vo) and lattice parameters (a and c) on pressure were obtained successfully. The lattice parameters of the polytypes and c/a ratio showed a same trend under the compression with a clear similarity between 4H and 6H. The total energy-volume and enthalpy-pressure relations were estimated. The calculated energy gaps showed a reduction in the band gap width of 4H and 6H with the pressure increase while 2H band gap increased gradually with pressure. The tendency toward decreasing the density of state (DOS) at the conduction band edge was similar among the polytypes. � 2017 Trans Tech Publications, Switzerland.

We explore the structural and electronic properties of a single layer arsenene using the state of art, first principle approach from density functional theory (DFT). All the calculation was conducted using an open source DFT code, adopted the planewaves (PWs) method by Quantum Espresso (QE). The calculation utilized an exchange correlation potential of electron parametrized by Perdew-Burke-Ernzerhof (PBE) under generalized gradient approximation (GGA) functional scheme. Meanwhile, the pseudopotential assigned for the core electron is the projector typed augmented wave with the core potential correction, generated using "atomic" code. All those parameters resulted an optimized structure of the honeycomb arsenene with lattice constant of 4.4971 Ǻ. The arsenene layer occupy a bond length value of 2.5964 Ǻ as measured between its neighbouring bonded atoms. From an optimized structure, we explore its electronic bandstructure plotted from 3 highly symmetries point for 2-dimensional (2D) material known as ‘Γ’, ‘Χ’ and ‘Κ’ with 3 electron pathways. The total number of bands considered in bandstruture plotting is 10, where 5 bands will be considered as valance bands while another 5 is conduction bands. The bandstructure shows that a single layer flat arsenene exhibits the characteristics of a conductor due to the overlapping of band near to Fermi level. Dirac cone were also noticed near to the Fermi energy level of the bandstructure. Lastly, we study the total electron density for the whole structure to reveal its bonding characteristics. The contour plot of electron densities between two bounded atoms displayed a pure covalent bond characteristic. The findings of this work is expected to contribute to the key of the electronic devices development, optoelectronics, and sensor devices based on 2D material technology. © 2020 Trans Tech Publications Ltd, Switzerland.

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.

We study the band structure of antiferromagnetic AxFe2Se2 (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 AxFe2Se2 will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the AxFe2Se2 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. � 2014 AIP Publishing LLC.

We make clusters of atoms of the size of less than 1 nanometer by using the density functional theory and from that we obtain the bond lengths corresponding to the minimum energy configuration. We are able to optimize large clusters of atoms and find the vibrational frequencies for each cluster. This calculation provides us with a method to identify the clusters present in an unknown sample of a glass by comparing the experimental Raman frequency with the calculated value. We start with the experimental values of the Raman frequencies of PSe (Phosphorous- Selenium) glass. We calculate the structural parameters of PSe, P4Se, P2Se2, P4Se5, PSe4, P4Se3 clusters of atoms and tabulate the vibrational frequencies. We compare the calculated values with those measured. In this way we find the clusters of atoms present in the glass. Sometimes, the same number of atoms can be rearranged in a different symmetry. Hence we learn the symmetries of molecules. We find that certain symmetries are broken due to self-organization in the glassy state. � (2013) Trans Tech Publications, Switzerland.