Electronic Band Calculations Research Articles

P-d hybridization of noble metal halides

The electronic band calculations of noble metal halides are studied to make the high ionic conducting origin of silver and cupper ions clear using the tight-binding method. The d bands of Ag ions are much more weakly coupled with the p bands of halogen ions, while those of Cu ions are much more strongly coupled with the p bands. The strength of p-d hybridization is discussed to connect with the activation energy for the ionic conduction. It is shown that the high ionic conductivity of AgX primary stems from combination of the deformability of the d shell and the weakness of the p-d hybridization.

Electronic band structure and de Haas–van Alphen effect of NiAs and NiSb

We have performed electronic band calculations for the paramagnetic NiAs and NiSb using the full potential LAPW method. The Fermi surface of each compound consists of two kinds of cylindrical-like hole surface around the ΓA -axis and one electron surface. For NiSb one more Fermi surface is obtained. The dHvA oscillation frequencies expected from each Fermi surface are calculated. Recently, we have measured dHvA oscillation for the single crystal of NiAs at 0.55 K in a field of up to 9.5 T and observed six branches. The observed results are discussed in comparison with the calculated results.

Electronic and magnetic properties of Li 2CuO 2

We have performed an electronic band calculation for non-magnetic (NM) and antiferromagnetic (AF) states of Cu–O edge-sharing compound Li 2CuO 2 by using the FLAPW method with local spin-density approximation (LSDA) and LSDA+U approximation. In the NM-state a narrow antibonding band crosses the Fermi level and consists of strongly hybridized Cu 3 d yz and O 2 p y states. The Fermi surface of the NM state reveals a nesting effect which plays an important role in causing the observed antiferromagnetic ordering. In the AF state the narrow antibonding band in the NM state is split and a small bandgap appears at the Fermi level. LSDA+U calculation leads to a much wider bandgap than the LSDA calculation.

Three-dimensional unoccupied band structure of graphite: Very-low-energy electron diffraction and band calculations

Three-dimensional unoccupied band structure of graphite: Very-low-energy electron diffraction and band calculations

Electronic Band Structure of Li2CuO2 and Application to Battery Electrode

The electronic band calculations of Li2CuO2 and Li-deintercalated CuO2 have been performed by the fullpotential linearized augmented plane wave (FLAPW) method within the local spin density approximation (LSDA). It is found that Cu 3d states are strongly hybridized with O 2p states and that Li atom is almost ionized. On the basis of the total energy calculations, we have studied the applicability of Li2CuO2 as a cathode material of rechargeable Li-battery. The average battery voltage in the chemical reaction, Li2CuCO2 → CuO2 + 2Li, is estimated. The structural stability is also discussed.

De Haas–van Alphen Effect and Electronic Band Structure of NiAs

We have measured the de Haas–van Alphen effect at 0.55 K in the field up to 9.5 T for the single crystal of Pauli paramagnetic NiAs. Six dHvA branches have been observed and they show complicated behavior as a function of the field direction which is applied in the symmetry planes (11\bar20), (10\bar10) and (0001). The corresponding cyclotron masses have been also determined from the temperature dependence of the dHvA amplitude. To discuss the experimental results we have performed the electronic band calculation of NiAs for the non-magnetic state by using the full potential LAPW method. The total energy calculated as a function of the lattice parameter a , keeping the ratio c / a as the observed value, becomes minimum at 3.60 A, which agrees very well with the observed one. The Fermi surface is found to consist of two kinds of hole surface around the ΓA axis and one electron surface with six fold symmetry. For each Fermi surface we have calculated dHvA oscillation frequencies and succeeded to explain the...

Low Temperature X-ray Studies of β1-Pd(dmit) 2 Salts

Structure analysis is performed at 8K and room temperature in the isostructural salts β1-(Me 4Z)[Pd(dmit) 2] 2 and β1-(Et 2Me 2Z)[Pd(dmit) 2] 2 (Z=P,Sb). The temperature effect on the dimerization of the Pd(dmit) 2 molecules is measured. The electronic band calculations show that the two-dimensional HOMO band remains the conduction band at low temperature as the energy gap between the HOMO band and the LUMO band is increased.

Electronic band structure of Li 2CuO 2

Electronic band calculations for non-magnetic and antiferromagnetic states of Li 2CuO 2 are performed by using the FLAPW method. Cu-3d states are strongly hybridized with O-2p states. For the non-magnetic state, a narrow antibonding band is separated from broad dp mixing bands and half filled with an electron. For the antiferromagnetic state, the calculated magnetic moment is extended on the CuO 2 chain.

Pressure effect on electronic band structures of NiAs-type CrTe, CrSe and CrS

The electronic band calculation of NiAs-type Cr-charcogenides is performed for non-magnetic, ferromagnetic and antiferromagnetic states by using the FLAPW method, and studied the pressure effect on the electronic structure. From the total energy calculated as a function of lattice parameter, pressure induced ferromagnetic → antiferromagnetic transition is expected in CrTe at about 40 GPa. In CrSe and CrS an antiferromagnetic state is most stable.

Transport properties ofBi1−xSbxalloy thin films grown onCdTe(111)B

We have grown ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ alloy thin films on $\mathrm{CdTe}(111)B$ over a wide range of Sb concentrations $(0l~xl~0.183)$ using molecular-beam epitaxy. Temperature-dependent electrical resistivity (\ensuremath{\rho}) and thermoelectric power (S) were studied. We have observed several differences over the bulk system. The 3.5 and 5.1% Sb alloys show semiconducting behavior, and the Sb concentration with maximum band gap shifted to a lower Sb concentration from 15% in bulk to 9%. Based on a simple interpretation of the temperature-dependent resistivity the maximum gap would be 40 meV, which is larger than that observed in bulk alloys. In addition, we have observed that the power factor ${S}^{2}/\ensuremath{\rho}$ peaks at a significantly higher temperature (250 K) than previously reported for the bulk alloy (80 K). Differences between thin film grown on CdTe(111) and bulk alloy may arise from the effects of strain, which is supported by theoretical electronic band calculations. These results show that BiSb films may be useful as band-engineered materials in thermoelectric devices.

High Pressure Measurements on TI2Mn2O7

AbstractTransport and structural properties of the colossal magnetoresistance pyrochlore TI2Mn2O7 are studied as a function of applied pressure up to ∼20GPa. This allows us to probe the effect of structural changes on the ferromagnetic transition and the transport properties. We observe a non-monotonous pressure dependence of the ferromagnetic transition temperature. We correlate this unusual variation with the structural parameters that, according to electronic band calculations, are key in controlling the properties of these materials.

First-principles study of structural stability and electronic properties of Sb/GaSb(111) semimetal–semiconductor superlattice

The structural stability and electronic properties of a (Sb2)2/(GaSb)2(111) semimetal–semiconductor superlattice are investigated by a first-principles all-electron linearized augmented plane-wave method within the local spin density functional approximation. When bulk values are used the two interfacial distances D1 and D2 are energetically unfavorable. The fully optimized structure shows that the bond lengths of Sb–Ga and Sb–Sb at interfaces are 1.3% and 2.8% longer than their bulk values, respectively. Further electronic band calculations of the stable (Sb2)2/(GaSb)2(111) superlattice show that the system has semimetallic behavior. A p-like interface band is observed below the Fermi level.

Chain Conformation and Metal…Metal Contacts in Dimers and Stacks of d8‐ML4Complexes: Electronic Effects

AbstractA qualitative theoretical study is presented of the ligand effects on the strength of the M…︁M nonbonded interaction in dimers and stacks of8‐ML4chains. It is found that π‐acidic ligands enhance and π‐basic ligands weaken the M…︁M bonding interaction. A large amount of structural data can be rationalized with the help of a simple orbital model. Other features of the crystal structures of such compounds are correctly accounted for by semiempirical molecular orbital and electronic band calculations (extended Hückel level). Electronic effects control the deviation from linearity of stacks of complexes with mixed ligands, whereas coupled electronic and steric effects determine the conformational preference. The predictive capability of theoretical band calculations is found to be good.

First principles calculation of effective mass parameters of GaN

First principles electronic band calculations are performed for the wurtzite and zincblende GaN, by using a full-potential linearized augmented plane wave method. In order to clarify the difference of electronic properties between two kinds of crystal structures, and to give important information on the characteristic analysis of GaN-based quantum well devices, the Luttinger-like valence band parameters, as well as the electron and hole effective masses and splitting energies, are derived from the calculated band structures with the assistance of the k·p theory, considering the cubic and hexagonal symmetries. The small spin-orbit coupling of a nitrogen makes us use the 6 × 6 k·p Hamiltonians for both structures in the analysis of the valence band states.

Electronic energy bands and lattice dynamics of pure and lithium‐intercalated InSe

AbstractA discussion of the electronic energy bands and lattice dynamics of pure and lithium‐intercalated InSe is presented. After a review of the structure of this material and its polytypes, experimental results on both optical absorption and photoluminescence are compared for the pure and lithiumintercalated cases. A similar comparison is made for experimental Raman spectra. Electronic energy band calculations based on the tight‐binding method are presented. The results indicate that InSe containing lithium has an impurity band just below the conduction band edge. The phonon dispersion curves of pure and lithium‐intercalated InSe have been calculated using the rigid ion model and the results compared with the Raman spectra. Normal modes associated with lithium impurity atoms are identified. A set of conclusions is presented.

Analysis of nuclear spin-lattice relaxation rates in transition metal dihydrides, TMH2 (TM = Sc, Ti, V and Nb) based on LAPW electronic band calculations

The spin-lattice relaxation rates (T1eT)−1 of transition metal nuclei 45Sc, 49Ti, 51V and 93Nb in cubic dihydrides ScH2, TiH2, VH2 and NbH2 are calculated on the basis of scalar-relativistic self-consistent LAPW band structure calculations. It is found that the s and p electron contributions to the relaxation rates are negligibly small for all the hydrides studied here due to their very low partial densities of electron states at the Fermi level. The d- orbital contributions are dominant and the core polarization and d-dipolar contributions play a minor role. The theoretical relaxation rates reproduce the experiments very well for ScH2 and TiH2 but less satisfactory for VH2 and NbH2. The experimental data were taken from our earlier studies and the results of additional measurements on 93Nb in NbH2 are reported. These have been made in the 30–292K temperature range and at a magnetic field of 7 T.

Topological Spin Polarization and a VB Picture of Infinite Model Systems for Organic Polymer Magnets in Terms of Electronic Band Calculations

Abstract This paper deals with a polymer version of the topological π-spin polarization interrelated to the topological superdegeneracy of crystal orbitals of infinite or extended polymeric spin systems and also with a VB picture of their spin structure in terms of simple electronic band calculations. We stress that the theoretical models (traveling wave approach) introduced predict essential features of magnetic properties of polymeric systems which yield crucial aspects for their materials design. The model calculation has also been made for various types of inter-polymer interactions in order to understand the topological spin polarization of higher-dimensional infinite or extended polymeric spin systems and the topological nature of inter-polymer contacts (inter-polymer connectedness). The results have shown that the connectedness gives rise to the prominent modulation of band structures and π spin polarizations which is highly dependent on the topology of the contacts. Thus, the results serve for mol...

Coexistence of electrons and holes in BaBi0.25Pb0.75O3- delta detected by thermoelectric-power measurements.

Seebeck coefficients of ${\mathrm{BaBi}}_{0.25}$${\mathrm{Pb}}_{0.75}$${\mathrm{O}}_{3\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (0.00\ensuremath{\le}\ensuremath{\delta}\ensuremath{\le}0.08) were measured as a function of temperature up to 1100 K in various ${\mathrm{O}}_{2}$ partial pressures. The Seebeck coefficient of ${\mathrm{BaBi}}_{0.25}$${\mathrm{Pb}}_{0.75}$${\mathrm{O}}_{3.00}$ below 300 K was negative by a few \ensuremath{\mu}V/K and showed linear temperature dependence, indicating a metallic or semimetallic nature of the carrier electrons. Above 300 K, the Seebeck coefficient (\ensuremath{\delta}=0.00) increased, becoming positive around 400 K. Curve fitting with an assumption of the coexistence of electrons that show delocalized character and holes that have a localized nature was carried out to determine the relationship between the Seebeck coefficients and the temperature of the sample. The temperature dependence of not only the Seebeck coefficient but also the electrical conductivity of the sample could be well explained by the assumption described above. From the comparison with electronic-band calculations, it is deduced that electrons with high mobility and holes with low mobility are the product of delocalized bands composed of Pb(Bi) 6s and O 2p antibonding orbitals and localized bands composed of O 2p isolated orbitals, respectively. The Seebeck coefficients of the samples with \ensuremath{\delta} values of 0.025--0.08 were also slightly negative at low temperatures and had values of \ensuremath{\sim}20 \ensuremath{\mu}V/K at around 1100 K. Finally, it could also be deduced that electrons and holes existed simultaneously in samples with an oxygen deficiency.

Two-dimensional angular-correlation-of-annihilation-radiation study of kappa -(BEDT-TTF)2Cu(NCS)2.

We report the two-dimensional angular-correlation-of-annihilation-radiation measurement of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ (pair) momentum distribution in the organic superconductor \ensuremath{\kappa}-(BEDT-TTF${)}_{2}$Cu(NCS${)}_{2}$. Our data, when compared with tight-binding (H\uckel) electronic-band calculations, show features consistent with predicted Fermi surfaces. The structure around Z in our spectrum supports the results from earlier de Haas--van Alphen and Shubnikov--de Haas measurements. In addition, our data show features consistent with the predicted open Fermi surface that runs nearly parallel to YM.

Structural Characterizations of Two Synthetic Ni-Ludwigites, and Some Semiempirical EHTB Calculations on the Ludwigite Structure Type

The structures of two novel synthetic nickel-containing borates, Ni2CrO2BO3 and Ni2VO2BO3, have been investigated by single crystal X-ray diffraction techniques and shown to have the ludwigite structure. The space group symmetry of both borates is Pbam with Z = 4. The unit cell dimensions are a = 9.209(1), b = 12.121(1), and c = 2.9877(3) Å, for the Ni,Cr-borate, and a = 9.199(2), b = 12.211(2), and c = 2.988(1) Å for the Ni,V-borate. The structural model of the Ni,Cr-ludwigite has been refined on the basis of the 575 most significant (I > 3σ(I)) reflections with sin(θ)/λ ≤ 0.9 Å,-1 to an R-value of 0.029. For the Ni,V-ludwigite refinement, the 617 most significant (I > 3σ(I)) reflections with sin(θ)/λ ≤ 0.8 Å-1 yielded an R-value of 0.023. Although the scattering powers of the cation pairs Ni/Cr and Ni/V are very similar, the refined cation distributions at the mixed metal sites yield approximately electroneutral compounds. The observed structural arrangement with the higher charged cations coplanar to the borate anion planes in the crystal structure is apparently a salient feature for all members of the pinakiolite structure family. A general model for the ludwigite structure, with alternating metal charges along the walls of octahedra, is supported by some semi-empirical extended Hückel electronic band calculations performed on the homometallic Fe- and Co-ludwigites.