Electronic band structure of InPxSb1−x alloys

The investigation of optoelectronic properties of zinc-blende InP_xSb_1−x, semiconducting alloys by pseudopotential calculations is studied. The scheme uses the local empirical pseudopotential method, which involves the disorder effect into the virtual crystal approximation by introducing an effective potential disorder. Various quantities for the alloy of interest are calculated. The obtained results show a reasonable agreement with the available experimental data. Special attention has also been given to the compositional dependence of these studied quantities.     

A soft-core Thomas-Fermi pseudopotential for total energy calculations

We present a modification of the “Thomas-Fermi pseudopotential” developed by Chelikowsky for the calculation of cohesive energies of solids. In the original work, the pseudopotential was singular at the origin, owing to a cusp in the pseudowavefunction. We derive here a “Thomas-Fermi pseudopotential” based on the form of pseudowavefunction introduced by Kerker, which is smooth and nonvanishing at the origin. This pseudopotential was tested in cellular calculations of the total binding energy and equilibrium cell size of bcc Na, both of which were in excellent agreement with experiment. The precision of the variationally determined charge density n(r) was checked by calculating the corresponding chemical potential μ(r), which was virtually uniform except in a small neighborhood of the origin. An LCAO parametrization of the charge density is outlined that would be appropriate for 3D problems such as a point defect.     

Ab initio calculation of structural, electronic and phonon properties of ZrRu and ZrZn in B2 phase

The structural, electronic and dynamic properties of cesium chloride, ZrRu and ZrZn were studied by employing an ab initio pseudopotential method and a linear response scheme, within the generalized gradient approximation. The calculated lattice constant, bulk modulus and first-order pressure derivative of the bulk modulus were reported in B2 structure and compared with available experimental and other theoretical results. The electronic band structure, partial and total density of states were determined by using the Quantum-Espresso ab initio simulation package based on pseudopotential method. Phonon dispersion curves and density of states were calculated by employing a density functional perturbation theory.     

Role of semicore electrons in the lattice dynamics of a cubic ZnS crystal

The phonon dispersion in a ZnS crystal has been studied by the density functional theory method with different pseudopotentials containing 10 (Zn¹²⁺) and 18 (Zn²⁰⁺) semicore electrons of the shell with the principal quantum number n = 3 in a zinc atom. It has been found that the pseudopotential of Zn²⁰⁺, unlike the pseudopotential of Zn¹²⁺ describes the phonon dispersion more accurately. An analysis has demonstrated that, in this case, the degree of d-p hybridization of semicore d states of zinc with the valence p states of sulfur decreases.     

Collisionally induced transition dipole moments of alkali-rare gas atom systems

The electronic transition dipole moments in alkali-rare gas atom systems have been calculated as a function of the internuclear distanceR. The pseudopotential method of Baylis with some refinements has been used in the calculation. In particular, the Bates-Damgaard functions used in the previous pseudopotential calculations of Baylis and Pascale et al. have been replaced by the more realistic atomic orbitals suggested by Simons. The results are presented graphically for the molecular transitions associated asymptotically (R→∞) with forbiddenS-S andS-D dipole transitions in the alkali atoms. The transition moments turn out to be relatively large at internuclear distances smaller thanR=12a₀.     

Electron correlation effects in the momentum distribution of highly oriented pyrolytic graphite

Absolute Compton profiles of highly oriented pyrolytic graphite have been determined using ¹⁹⁸Au 412 keV gamma radiation. The anisotropy in the electron momentum density between Compton profiles measured parallel to the c-axis and averaged over the basal plane have been compared with a recent pseudopotential calculation of Chou et al. Excellent agreement is found over the entire momentum range studied. Differences between absolute Compton profiles J_theory(p_z − J_exp (p_z) vindicates a correlation correction to take account of the electron-electron Coulomb interactions.     

The limiting compression in single shocks for sp metals

The slope of the linear curve relating shock velocity and particle velocity in shock wave experiments has been examined by the pseudopotential energy band method for sp metals. The limiting density ration resulting from this linear relation is interpreted by defining a shock “hard core” for single shocks and its relation to Ashcroft's core radius is examined.     

Electronic properties of silicon with ultrasmall germanium clusters

The electronic states of silicon with a periodic array of spherical germanium clusters are studied within the pseudopotential approach. The effects of quantum confinement in the energies and wave functions of the localized cluster states are analyzed. It is demonstrated that clusters up to 2.4 nm in size produce one localized s state whose energy monotonically shifts deep into the silicon band gap as the cluster size increases. The wave function of the cluster level corresponds to the single-valley approximation of the effective-mass method. In the approximation of an abruptly discontinuous potential at the heterointerface, the quantities calculated using the effective-mass method for clusters containing more than 200 Ge atoms are close to those obtained by the pseudopotential method. For smaller clusters, it is necessary to take into account the smooth potential at the interface.     

Optical spectra and Auger recombination in SiGe/Si heterostructures in 10 μm range of wavelengths

We discuss the possibility of usingp-type SiGe/Si multiple quantum well structures for infrared detection. We calculated the miniband dispersion in these structures using an empirical pseudopotential method including the effects of spin and strain. The absorption spectra of these structures is discussed and the microscopic origin of the absorption peaks identified. We present comparisons between our calculated absorption response and the experimental spectra obtained in recent experiments for both parallel and normal incidence light. We also report full-scale pseudopotential calculations of the Auger recombination in these structures and present a fresh discussion of the conditions which could help to minimize this recombination.     

Y3Al5O12的热输运性质的第一性原理研究

基于密度泛函微扰理论（DFPT）结合模守恒赝势方法进行晶格动力学模拟.得到了钇铝石榴石（YAG）的声子态密度、分波声子态密度和声子的色散谱.利用第一Brillouin区的特殊点取样方法,计算了YAG的比热容和布局数平均的声子群速度.在非谐相互作用下,利用Fermi黄金公式结合第一Brillouin区的特殊点取样方法,得出了YAG非谐声子平均自由程.综合考虑了两种声子散射机制,得到了YAG陶瓷的热导率.结果表明,对于YAG陶瓷,在低温时,晶界散射将对热阻起主要作用;在高于一定温度时,三声子相互作用对热阻的贡献将占主导地位.同时也从理论上证明了Sato等提出的在室温以上,YAG陶瓷与单晶的热导率的差异可以忽略的观点.所得到的热导率、比热容随温度的变化与实验结果很好地符合. 关键词： 声子平均自由程 密度泛函微扰理论 3Al₅O₁₂声子结构')" href="#">Y₃Al₅O₁₂声子结构 热导率     

Valence charge density in indium arsenide

Valence charge densities of zinc-blende structure InAs calculated using an ab initio pseudopotential method are reported. It is found that as zinc-blende structure InAs is compressed, the changes in the charge density are gradual even as the volume at which it is unstable in favour of a rock salt structure is passed, and that under pressure the bond charges tend to move away from the anion sites towards the bond center sites.     

Pseudopotential approach to magnetic energy bandstructure and magnetic breakdown in metals

The orthogonalized plane wave method of energy bandstructure calculation is generalized to the case of a metal under the influence of an external de magnetic field, with the magnetic translational symmetry taken into account fully. The magnetic field-dependent effective lattice potential or pseudopotential derived from it is interpreted as a “magnetic” pseudopotential and shown to depend only weakly on the magnetic field strength so that, to a good approximation, it can be replaced by an ordinary pseudopotential, and treated as a perturbation in the calculation of magnetic energy bands and galvanomagnetic properties in nearly-free-electron metals. Physical properties connected with the phenomenon of magnetic breakdown, in particular the Landau level broadening, which were previously shown by Pippard, Zak and others to be proportional to an unspecified pseudopotential, are reformulated in terms of the magnetic pseudopotential. The convergence of the method is also discussed.     

Knight shifts of metals in the liquid state

A single orthogonalized plane wave calculation has been made, to zero order in the pseudopotential, of the direct contact Knight shift for 30 liquid metals. The average deviation from experimental values is approximately 15%. Larger unexplained divergences occur for Cu and Hg. In addition it is shown that to zero order in the pseudopotential the factorΩP _F in the Knight shift describing the electron density at the nucleus is almost unaffected by thermal expansion.     

Semi-empirical APW calculation of the band structure of silicon

We propose a modification to the usual augmented-plane-wave muffin-tin approximation approach which fits exactly the measured value of the band gap of Si. The method involves one adjustable parameter which is introduced by a uniform shift of the s-like logarithmic derivatives. The results are in good agreement with those of the empirical pseudopotential method not only for the gap but also for an energy range of approximately 3eV from the top of the valence band.     

The low field Hall-effect of poly-valent metals in the nearly free electron approximation. I: Al,In and Pb

The formula by Tsuji for the low field Hall-coefficient is applied for tri- and tetra-valent metals in thefcc structure. Under the assumption of sufficient small pseudopotential the evaluation of the Tsuji formula is rather simple. The Fermi-surface can be divided into different parts; the free electron sphere and the ring shaped distorted parts at the intersection circles with the Bragg-planes. The latter represent electron-like and hole-like carriers; the Bragg-particles. The actual Hall coefficient is a sum of the free electron Hall-coefficientR _o and the contribution of the Bragg-particles. The latter is of the same order of magnitude asR _o. Its sign depends on the actual scattering potential and on the sign of the pseudopotential. A successful comparison with experimental results for Al, In and Pb is given for impurity scattering. thermal scattering and temperature dependence. A measurement of the Hall-effect under pressure is suggested to prove the dominant role of the sign of the pseudopotential for the Hall-effect.     

Electronic structure of black phosphorus studied by X-ray photoelectron spectroscopy

The X-ray photoelectron spectrum of black phosphorus has been measured for the first time. The features in the valence band spectrum are found to be in good agreement with those of the valence state density recently calculated on the basis of a pseudopotential method. The 2s and 2p core spectrum of black phosphorus is also discussed.     

Band structure of semiconductor alloys beyond the virtual crystal approximation. effect of compositional disorder on the energy gaps in GaPxAs1−x

A general method to study the band structure of compositionally disordered semiconductors is proposed. The effects of chemical disorder are added to the virtual-crystal band structure using the pseudopotential method and second order perturbation theory. In GaP_xAs_1?x, chemical disorder is shown to give a significant contribution to the experimentally observed non-linear behaviour of the lowest energy gaps as function of composition.     

Phonon dispersion in thorium: A pseudopotential approach

A one parameter model pseudopotential is used in investigating the phonon dispersion in thorium. A very good agreement has been obtained between theory and experiment, especially, in transverse branches. This is attributed to the removal of the discontinuity in the pseudopotential in r-space.     

Energy band structure of cadmium fluoride

The electronic band structure of cadmium fluoride is calculated by a combined tight binding and pseudopotential method. The band structure is found to be rather similar in shape with that of CaF₂. In particular it is shown that the occupied cationic d⁺ bands do not perturb significantly the upper valence band predominantly composed of the F^-p-orbital. This explains the great similarity of the low energy part of the reflection spectra of CaF₂ and CdF₂.     

Pressure shifts of F-center hyperfine interaction parameters in alkali chlorides

We report here calculated values of the pressure shift in the shell I hyperfine interaction constants for F-centers in KCl, NaCl and LiCl. The calculation is based on a modified version of the pseudopotential approach of Bartram et al. with electronic polarization included by means of an r-dependent polarization potential. The results agree reasonably well with the available experimental data, and the strong dependence of the pressure shift on ion size ratio is shown to be mainly due to changes in the indirect-overlap contributions to the spin density. These terms result from the requirement of mutual orthogonality of core states on neighbouring ions, and their dependence on the lattice spacing is stronger than that of other contributions to the spin density. Our calculations further indicate that although the predicted value of the pressure shift is sensitive to errors in the pseudopotential and polarization parameters, the relative importance of the indirect overlap contributions is evident in spite of such errors.