Linear Muffin-tin Orbital Method In The Atomic Sphere Approximation Research Articles

A new study of the optical and structural characterization properties of p-type ZnS2 pyrite with an application in solar energy

Abstract In this manuscript, we study the grouping of bands and optical properties of p-type Zn S 2 pyrite, which helps us in the study of crystal p-type Zn S 2 pyrite and its impact in organic photovoltaic cells. Our work has two approaches one theorical where we find the band structure of p − type Zn S 2 by using linear muffin-tin orbital method in the atomic-sphere approximation (LMTO-ASA), the second approach is the experimental where we prepare the crystals by chemical vapor transport. The sample was examined by XRD and optical characterizations. Our results show that the p-type Zn S 2 pyrite is a direct semiconductor with optical gap about 1.610 eV and calculated gap about 1.550 eV . As an illustration of our finding, we present an application of our work to photovoltaic devices.

Impact of zinc structural on the photovoltaic Properties of iron Pyrite

FeS2 pyrite is one of the most interesting photovoltaic materials with low-cost and natural abundance but with small band gap of 0.95 eV. In the present work, we show the feasibility of increases band gap was determined by Zinc alloying of Iron pyrite. We showed that we can increase the band gap of FeS2 pyrite to 1.15eV by theoretical calculation and to 1.16eV using experimental method, by just adding a very small amount of Zinc (1%). We prepared our samples by chemical vapor transport technic and we utilized the technic of linear muffin-tin orbital method in the atomic-sphere approximation (LMTO-ASA). The effect of Zinc alloyed Iron pyrite were examined by transmission electron micrograph TEM, XRD, Raman spectroscopy and optical characterization.

An Insight of the Theoretical Physics of Ru-Alloyed Iron Pyrite Studied for Energy Generation

Pyrite FeS2 has become the focus of many researchers in thin-film photovoltaics because it has some possibilities in photovoltaics. In this manuscript, we present an experimental and a theoretical study of the electronic structure of pyrite FeS2 alloyed with a small concentration of 1.19% of ruthenium (Fe0.9881Ru0.0119S2) by using the Linear Muffin-Tin Orbital Method in the Atomic-Sphere approximation (LMTO-ASA) calculations and the density of states. We observed that the bandgap of FeS2 increases from 0.90508 to 1.21586 eV when we replace ~1.19% of the Fe atoms with ruthenium atoms x=0.0119 concentration of Ru. We prove that this low concentration of Ru saved the gap states and the electronic and optical properties of FeS2 pyrite. Our calculated electronic bandgap is 1.21586 eV and direct. Our results confirm that the symmetric operation of the space Th6 Pa3 saves electronic structure of iron pyrite when alloyed with ruthenium.

Electronic structure of iron pyrite by the LMTO_ASA method

We obtain the self-consistent band structure and density of states of iron pyrite FeS2 using the linear muffin-tin orbital method in the atomic-sphere approximation (LMTO-ASA). Both the electronic structure and density of states are discussed in detail. The calculated band gap is direct, with a width of 0.90508 eV. These results agree with experimental measurements. The calculated density of states shows that the valence band is fully occupied while the first conduction band is unoccupied.

First-principles study of photoconductivity in BaTiO 3 with oxygen vacancies

The photoconductivity of BaTiO 2.5 with oxygen vacancy has been studied by the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The ground-state structure of BaTiO 2.5 is obtained by minimization of the total energy. The partial densities of states show that the occupied states at the bottom of the conduction band have primarily Ti d orbital character. The photoconductivity shows that two novel features, in the low energy side, can be attributed to the intraband transition of free electronic carriers in the vicinity of the Fermi level and the interband transition of the Ti 3d( yz) related band states, to the Ti 3d( xy, xz) related band states, respectively. In addition, it is also found that the anisotropy of photoconductivity is enhanced because of the introduction of oxygen vacancy. The system can show the conductive behavior of electronic carriers, which is qualitatively in agreement with a recent experimental finding.

The self-consistent band structure of PtSSe by the linear muffin-tin orbital method in the atomic sphere approximation

The self-consistent band structure and the density of states of the layer compound PtSSe were calculated using the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). This calculation includes the relativistic mass-velocity and Darwin terms but excludes the spin-orbit coupling. The Barth-Hedin local exchange correlation potential was used. The result, reported for the first time, predicts that PtSSe is a semiconductor with an energy gap of about 0.64 eV. Such a behaviour is confirmed by the experimental data available. The self-consistent band structure of PtS2 and PtSe2 were calculated, by the same method, and the effect of the anion substitution in the sequence PtS2PtSSePtSe2 have been studied. The results are discussed in terms of charge transfer and local coordination of the constituent atoms.

Copper tubules and local origin of a pseudogap ind−AlCuCofromab initiocalculations

We examined in great detail various stoichiometric variants of the Burkov model based on the T\"ubinger triangle tiling. We present density of states calculated with the linear muffin-tin-orbital method in the atomic sphere approximation (LMTO-ASA) method on 1/1 approximants. We define a subset of the Burkov model which exhibits a clear pseudogap at the Fermi level, as shown in measurements of photoemission spectra. All the resulting systems contain pure copper tubules in the direction perpendicular to the quasicrystalline plane. We show that the appearance of a gap is due to two distinct mechanisms: A Hume-Rothery-like one for the $s$ and $p$ states and a $\mathrm{Al}\ensuremath{-}sp\ensuremath{-}\mathrm{Co}\ensuremath{-}d$ hybridization in certain cobalt clusters, leading to a wide splitting of the $d$ states at that specific site. We comment on the spiky structure of the presented density of states (DOS) and the projected DOS and demonstrate the artificial appearance of spikes in LMTO-ASA calculations on simple model systems.

Toward a total energy tight-binding Hamiltonian based on the linear-muffin-tin-orbital method

We have investigated the accuracy of approximations involved in constructing a total energy tight-binding Hamiltonian for AuCu based on the linear-muffin-tin-orbital method in the atomic-sphere-approximation (LMTO-ASA). The approximations involved in constructing the tight-binding Hamiltonian are broken into four stages: (i) the use of the LMTO-ASA method, (ii) the use of only the first-order LMTO-ASA Hamiltonian, (iii) the use of non-self-consistent potential parameters, (iv) the use of a fit repulsive term. The equations of state are calculated for 11 different structures and compared at each stage of approximation. The results show that for AuCu the tight-binding Hamiltonian produces significant overbinding and errors in the equation of state.

Electron and positron characteristics of group IV metal dihydrides

Self-consistent calculations of the electronic structure of TiH 2, ZrH 2 and HfH 2 were performed by the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The band structure of non-stoichiometric ZrH 1.75 was calculated as well. The effect of a hydrogen vacancy on the electron characteristics of zirconium dihydride was analyzed. The positron states, lifetime and the contributions of electron states to the electron-positron annihilation (EPA) processes were calculated in low positron density approximation. The results obtained are in satisfactory agreement with the experimental and other theoretical data.

Electronic structure and hyperfine interactions of 3d transition element ions in CdTe

We present ab initio total energy calculations for the 3d transition metal (TM) defects on the Cd site in CdTe. Our calculations are performed using the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA) and are aimed at the theoretical calculation of hyperfine and ligand hyperfine interactions (HFIs). Our calculations show that although the 3d TMs are covalently bound to the nearest-neighbour (NN) Te ligands, the HFI with these Te ligands is very small and corresponds to of a spin at most. The ligand HFI with the next-nearest-neighbour (NNN) Cd nuclei is even smaller in most cases than that with the Te ligand nuclei. We show for the case of that it is not the small natural abundance of paramagnetic Te nuclei which prevents the experimental observation of the ligand HFI with the nuclei, but rather the fact that the HFI lines for the interaction with the NN ligand nuclei coincide with interactions with the NNN and ligand nuclei. This prevents the observation of larger HFIs with the NN Te ligands although the smaller HFI with the NNN Cd ligands is clearly resolved.

Electronic structure and enhancement of magnetic moments in the ferromagnetic nitride Fe16N2.

The electronic structure of ${\mathrm{Fe}}_{16}$${\mathrm{N}}_{2}$ is calculated by using the linear muffin-tin orbital method in the atomic-sphere approximation (LMTO-ASA). Both the standard local-spin-density approximation (LSDA) and the recently proposed generalized gradient approximation (GGA) are used in this density functional calculation. By introducing the gradients of the density, the exchange-correlation effect is taken into account more sufficiently in GGA than in LSDA. Magnetic moments at three different sites of Fe atom (i.e., Fe I, Fe II, Fe III) are 2.20, 2.55, and 2.70${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, respectively. Larger enhancement of magnetic moment is obtained in Fe II and Fe III, which are located farther from N than Fe I. There is no significant difference in magnetic moments and density of states between the two approaches (GGA and LSDA).

Using generalized gradient approximation method to study the electronic structure of ferromagnetic nitride Fe/sub 16/N/sub 2/

The electronic structure of Fe/sub 16/N/sub 2/ is calculated by using the linear muffin-tin orbital method in the atomic-sphere approximation (LMTO-ASA). The recently proposed generalized gradient approximation (GGA) is used in this density functional calculation. In the GGA method, through considering the gradients of the density, the exchange-correlation effect is taken into account more sufficiently than in the standard local-spin-density approximation (LSDA). The total energy calculated with GGA is lower than that with LSDA. Magnetic moments at three different sites of Fe atom (FeI, FeII and FeIII) are 2.20, 2.55, and 2.70 /spl mu/B respectively. Large enhancements of magnetic moment are observed in FeII and FeIII, which are located farther from N than FeI. There is no significant difference in calculated magnetic moments and density of state between the two approaches (GGA and LSDA).

The electronic and magnetic properties of the metamagnetic ordered alloy FeRh

The band structure and total energy of the metamagnetic ordered alloy FeRh were calculated by the self-consistent spin-polarized linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The total energy and magnetic moments were found as functions of volume in the antiferromagnetic and ferromagnetic states. The Fermi surface was found at ambient and high pressures. Based on the band structure the free energy of the system was calculated for finite temperatures to obtain the phase diagram in the (T,p) plane.

The calculation of the electronic structure of zirconium dioxide in cubic and tetragonal phases

A self-consistent calculation of the electronic structure of zirconium dioxide in cubic and tetragonal phases has been performed by the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA). The band structure, total and partial densities of states, partial charges and optical conductivity in the constant-matrix-element approximation have been calculated. The variation of electronic characteristics as a function of the displacement of the oxygen atoms in the tetragonal phase has been analyzed. The effect of oxygen vacancies and of yttrium or magnesium substitutional impurities on the electronic structure and optical properties of cubic zirconium dioxide has also been studied.

Pressure-induced phase transformations in alkali-metal hydrides calculated using an improved linear-muffin-tin-orbital-atomic-sphere-approximation energy scheme.

A scheme for the calculation of total energies from first principles is described which is intermediate between the popular linear muffin-tin-orbital method in the atomic-sphere approximation (LMTO-ASA) and an exact full-potential treatment. The local-density total energy is evaluated accurately for the output charge density from the ASA potential. This method is applied to the study of static structural properties and the pressure-induced phase transformation from B1 (NaCl-structure) to B2 (CsCl-structure) phases for the partially ionic alkaki-metal hydrides NaH and KH and the alkali halide NaCl. Good agreement with experimental transition pressures and volumes is obtained. The series NaH, KH, and NaCl shows the observed strong cation and weak anion dependence. Charge densities and band structures are given at zero and high pressure. Calculated energy-volume curves for LiH show no transition up to 1 Mbar, in agreement with experimental data.

Effects of structure and doping on the electronic properties of La2CuO4 and Nd2CuO4

We have calculated the electronic structure of Nd 2 CuO 4 in the observed T' structure and also in hypothetical T and T ∗ structures with the linear-muffin-tin-orbital method in the atomic-sphere-approximation (LMTO-ASA). We also studied in these local density approximation (LDA) calculations the effects of Ce and Sr doping by supercell calculations. We find that the O partial density of states of the NdO 2 planes substantially shifts in energy as a function of doping and structure. By comparing our results with a similar study on La 2 CuO 4 , we note that the position of the Ln 5d states (Ln=La, Nd) through hybridization with the 2p O states in the LnO 2 planes, determines the energy shifts of these O p bands. Upon doping with Ce or Sr, the metal d-oxygen p hybridization in the Nd 1− x Ce x O 2 and Nd 1− y Sr y O 2 planes gives rise to a local energy shift of the O p bands.

Electronic Structure of Epitaxial Silicon Interfaces

ABSTRACTUsing the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA), we studied the electronic structure of the Si(111) interface for four different materials: CaF2, NiSi2, CoSi2, and YSi2. We examined how the interface states and Schottky barrier height depend on the interface atomic structure.