Empirical Tight-binding Method Research Articles

Zero-Magnetic-Field Spin Splitting of Conduction Subbands in InGaAs/InAlAs and GaAs/AlGaAs Quantum Wells

Zero-magnetic-field spin splitting in InGaAs/GaAs and GaAs/AlGaAs multiple quantum wells was investigated theoretically. The sp3s* empirical tight-binding method has been employed. It has been found that the splitting is much larger in InGaAs wells than that in GaAs wells. The origin of the splitting due to the structure inversion asymmetry was briefly discussed.

807 シリコン単結晶のせん断変形に対する原子間ポテンシャルの妥当性

Shear deformation of a single crystal silicon is analyzed using the empirical Tersoff potential Tight-binding (TB) method and ab-initio calculation. As a result of using the Tersoff potential and TB method with the Wang's TB potential, the energy changes of a twining mode are different from the ab-initio results. It is found that these potentials can not represent the reasonable stress state under the highly shearing strain. TB calculations shows that the bond breaking process at the relaxation of atomic configurations is obtained, which is in good agreement with the ab-initio results.

A tight-binding representation of electron-hole exchange interaction in semiconductors

The electron-hole exchange interaction in semiconductors is analyzed in the framework of the empirical tight-binding method. It is demonstrated that intra-atomic and interatomic contributions to the long-range exchange interaction enter in an inequivalent way. In particular, for the Γ6×Γ7 exciton in a spherical nanocrystal with a cubic lattice, the dipole-dipole contribution associated only with the intra-atomic (or intra-site) transitions does not lead to singlet-triplet splitting of the exciton level. The interatomic transitions, for example, anion-to-cation transitions between the nearest neighbors in binary semiconductor compounds, determine the so-called monopole-monopole contribution to the exchange splitting of the Γ6×Γ7 exciton, and this contribution does not vanish in a spherical nanocrystal.

Adsorption of Water on Single and Double Layer Stepped Si(100) Surfaces

We have investigated possible water adsorption forms on SA, DA and DB type stepped Si(100) surfaces. Calculations are performed using the empirical tight binding method. Two types of adsorption models of water on stepped Si(100) surfaces have been considered: the dissociative type (H, OH) and the molecular type (H2O). The results of the density of states indicate a dissociative type of water adsorption on SA, DA and DB type stepped Si(100) surfaces.

ADSORPTION OF HYDROGEN AND OXYGEN ON SINGLE AND DOUBLE LAYER STEPPED SI(100) SURFACES

We have investigated the electronic band structure of hydrogen and oxygen adsorbed single and double layer stepped Si(100) surfaces by Empirical Tight Binding (ETB) method. The total electronic energies of the H,O-SA, DA, DB type stepped Si(100) systems are calculated with limited number of hydrogen and oxygen atoms separately to find out the most probable adsorption sites of the adatoms in the initial stage of hydrogenation and oxidation.

Electromagnetic coupling and gauge invariance in the empirical tight-binding method

Electromagnetic coupling and gauge invariance in the empirical tight-binding method

ADSORPTION OF WATER ON SINGLE AND DOUBLE LAYER STEPPED Si(100) SURFACES

We have investigated possible water adsorption forms on SA , DA and DB type stepped Si(100) surfaces. Calculations are performed using the empirical tight binding method. Two types of adsorption models of water on stepped Si(100) surfaces have been considered: the dissociative type (H, OH) and the molecular type ( H2O ). The results of the density of states indicate a dissociative type of water adsorption on SA , DA and DB type stepped Si(100) surfaces.

Electronic Band Structure of Stepped Si(100) Surfaces

We have investigated the electronic band structure of five different stepped Si(100) surfaces by the empirical tight binding (ETB) method. It has been found that the interaction states have approximately the same energy values for the stepped surfaces with a similar dimer bond nature on the terraces. The single layer stepped models show different density-of-states features than the double layer stepped models.

ELECTRONIC BAND STRUCTURE OF STEPPED Si(100) SURFACES

We have investigated the electronic band structure of five different stepped Si(100) surfaces by the empirical tight binding (ETB) method. It has been found that the interaction states have approximately the same energy values for the stepped surfaces with a similar dimer bond nature on the terraces. The single layer stepped models show different density-of-states features than the double layer stepped models.

Full multiband simulation of quantum electron transport in resonant tunneling devices

We present a formulation and calculations of multiband quantum transport of electrons in resonant tunneling diodes (RTDs) based on a non-equilibrium Green function theory. In the formulation we have used an empirical tight-binding method to include a realistic band structure, where evanescent-wave matching at heterointerfaces, Γ– X valley-mixing effects, and space charge effect are duly taken into account. Our results show that the current–voltage characteristics of a GaAs/AlAs double-barrier RTD has a larger current density than the conventional single band (SB) model since the latter is found to overestimate the decay constant in the barriers. Note that matching of evanescent electron modes essentially requires the inclusion of valley-mixing effects for GaAs/AlAs heterostructures owing to breaking of lattice-translational symmetry occurring at interfaces.

Stability, electronic structure and reactivity of the polymerized fullerite forms

A study of band structure, stability and electron density distribution from selected crystal orbitals of polymerized C60 forms was carried out. Linear chain, tetragonal and hexagonal layers, and three-dimensional (3D) polymer with a simple cubic lattice were calculated using an empirical tight-binding method. The hopping parameters were chosen to fit a theoretical X-ray emission spectrum of C60 to the experimental one. Our results indicate that all calculated polymers are semiconductors with the smallest energy gap for hexagonal structure. Though the molecules C60 are linked by strong covalent bonds, the crystal orbitals characterized by the electron density localization on an individual carbon cage are separated in the electronic structure of polymers. The suggestions about reactivity of the 1D and 2D tetragonal polymers were made from the analyses of crystal orbitals accompanied with the highest occupied (HO) and lowest unoccupied (LU) bands. The polymerized C60 forms were found to be less stable than an icosahedral fullerene molecule.

Absorption coefficient of wurtzite GaN calculated from an empirical tight binding model

The linear absorption coefficient for polarizations parallel and perpendicular to the c-axis of wurtzite GaN is calculated by integrating the momentum matrix element over the full Brillouin zone using a fundamental numerical technique. The energy band structure and wave functions required for this calculation are obtained using an sp 3d 5–sp 3 empirical tight-binding method (ETBM) that includes the spin–orbit and up to second-nearest-neighbor interactions. The model reproduces the selection rules expected from symmetry considerations.

Exact representation ofexp(iq⋅r)in the empirical tight-binding method and its application to electromagnetic interactions

We show how the exact representation of the operator $\mathrm{exp}(i\mathbf{q}\mathbf{\ensuremath{\cdot}}\mathbf{r})$ in the Bloch sum basis used in the empirical tight-binding method follows from the transformation law obeyed by cell-periodic operators, such as the Hamiltonian. From this representation, we derive matrix elements of its product with cell-periodic operators, since product operators of this type arise when the crystal is subject to various perturbations. Using these results, we calculate the expression for the linear transverse dielectric tensor.

Tight-binding calculations of electronic properties of AgI

The empirical tight-binding method is used to calculate the electronic band structure, density of states, and dielectric response function of AgI. Effective masses of electrons and holes, and the refractive index are also calculated. The results are compared with other calculations.

Adsorption of Oxygen and Hydrogen on Stepped Si(100) Surface

We have investigated the electronic band structure of oxygen and hydrogen adsorbed stepped Si(100) surface using the empirical tight binding method (ETB). The total electronic energies of the O-stepped and H-stepped Si(100) systems are calculated with a limited number of oxygen and hydrogen atoms separately to find out the most probable adsorption sites of the adatoms in the initial stage of oxidation and hydrogenation.

Adsorption of Oxygen and Hydrogen on Stepped Si(100) Surface

We have investigated the electronic band structure of oxygen and hydrogen adsorbed stepped Si(100) surface using the empirical tight binding method (ETB). The total electronic energies of the O-stepped and H-stepped Si(100) systems are calculated with a limited number of oxygen and hydrogen atoms separately to find out the most probable adsorption sites of the adatoms in the initial stage of oxidation and hydrogenation.

Trimerization of C 60

Seven different regioisomers of C 60 trimers with intact cages have been calculated at the empirical tight-binding total energy calculation method. We analyze the atomic structure and energetics of seven different trimers except the sterically demanding cis-1. The trimers are formed by the linkage through a [2+2] cycloaddition. The energies of the trans-3, trans-1, trans-2, trans-4, cis-3 and cis- 2 regioisomers relative to the most stable equatorial regioisomer are 13, 19, 20, 30, 207 and 673 meV, respectively.

Adsorption of water on stepped Si(100) surface

We have investigated possible water forms on stepped Si(100) surface. Calculations are performed by using the empirical tight-binding method. Two types of adsorption model of water on stepped Si(100) surface have been considered; one of them is the dissociative type (H, OH) and the other is the molecular type (H 2O). The results of the density of states supported by total electronic energy calculations indicate a dissociative type of water adsorption on the stepped Si(100) surface.

Effective masses of wurtzite GaN calculated from an empirical tight binding model

The energy band structure of wurtzite GaN is calculated using an sp 3d 5 - sp 3 empirical tight-binding method (ETBM) that includes the spin-orbit interaction. The model incorporates all nearest-neighbor and some second-nearest neighbor interactions within the two-center approximation. The second-nearest neighbor interactions excluded are the cation-cation interactions involving the Ga 3 d orbital. The effective masses of the conduction and A, B, and C valence bands have been calculated and found to be in good agreement with published experimental data.

Electronic structure of BN, BP and BAs

The empirical tight-binding method is used to investigate the electronic structure of the zinc-blende boron compounds BN, BP and BAs. Results are given for band structures, ionicity factors and elastic constants. The electronic structure of the boron compounds exhibits features that differ from those of the other III–V materials. In particular we found that these compounds are characterized by a strong cation-anion s–s repulsion effect. The calculated ionicity shows a weak charge transfer effect for BP and BAs which makes these compounds as the prototype covalent materials of the III–V family, while BN is found more ionic.