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.     

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.     

Classical modelization of symmetry effects in the dense high-temperature electron gas

A Kramerslike classical pseudopotential which includes Diffraction and Symmetry effects is worked out for k_BT?1 Ry.     

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.     

One-electron energies in the presence of electron-phonon interactions

Decoupling of an electron-ion interacting system is considered and the pseudopotential method of Phillips and Kleinman is extended to include the effect of electron-phonon interactions. It is shown that the effective potential experienced by a decoupled electron is the instantaneous pseudopotential averaged over all possible phonon states. The averaged pseudopotential is not only periodic but also temperature-dependent. After decoupling, a simple procedure for calculating single-electron excitation energies resulting from the coupling term is given and the result is formally in agreement with that obtained by Green's function method.     

Thermotransport of Ag,In and Sb in liquid Sn

A pseudopotential based model of the electronic contribution to the thermotransport in liquid metal alloys is proposed. The temperature variation of the experimental heat of transport Q¹ allows one to separate the so-called intrinsic and electronic parts of Q¹.     

Static structure factor and electronic transport properties of liquid rubidium from a first principles pseudopotential calculation

A first principles nonlocal pseudopotential calculation is used to obtain the ion-ion potential for liquid rubidium of 45°C. This is then used in a Monte Carlo simulation to determine the liquid structure S(q) and transport properties. It is found that the accuracy of the S(q), in the low q-region, is crucial to the calculation of electronic transport properties.     

Ab initio study of the structural properties of magnesium

Structural properties of magnesium in the hcp structure are calculated using the ab initio pseudopotential method within the local-density-functional formalism. The calculated lattice constants, cohesive energy, bulk modulus, and Poisson's ratio are in good agreement with experimental values. A comparison with the results of beryllium is also discussed.     

Pseudopotential band structure of solid solutions SnSxSe2−x

A very satisfying agreement with the experimental optical data is obtained from a priori pseudopotential calculations for SnS_xSe_2?x solid solutions. The band structure of SnSe₂ is also computed and previous results for SnS₂ are improved.     

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 new scheme for calculation of effective pair potentials for liquid metals

A new scheme based on the Singwi et al. theory for an interacting electron gas is proposed for calculating pair potentials for liquid metals and applied to liquid sodium and rubidium. The resulting pair potentials are in much better agreement with the pseudopotential calculations than any of the three usual approximations, PY, HNC or BG used in the literature.     

Electron states on the (111) surface of copper

A calculation of electronic states at the (111)-surface of Cu in the energy region around E_F is presented. The calculation is based on the empirical pseudopotential method. A proper position of an abrupt potential barrier ensures overall charge neutrality. A surface state is found at 0.13 eV below E_F, being localized midway between atomic layers. The effective mass of the associate bands is 0.39m_e. Our results are in good agreement with directional photoemission data.     

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.     

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.     

Calculation of the atomic radius from shielding considerations

A simple empty core Thomas Fermi pseudopotential is used to calculate the value of the radius of the atom in the simple and transition metals. In a given atom the extent of the atomic core is taken equal to the distance from the nucleus at which the outermost node in the wave function of an s valence electron occurs. It is found that this parameter is simply related to the depth of the potential well for s electrons obtained by the model potential authors for the simple and transition metals.     

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.     

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.     

Temperature dependence of the short-range order parameter and the concentration dependence of the order-disorder temperature for NiPt and NiFe systems in the improved statistical pseudopotential approximation

The calculations for the temperature dependence of the first shell short- range order (SRO) parameter for Ni₃Fe using the cubic approximation of Tahir Kheli, and the concentration dependence of order-disorder temperature T_c for NiFe and NiPt systems using the linear approximation, have been carried out in the framework of pseudopotential theory. It is shown that the cubic approximation yields a good agreement between the theoretical prediction of the α₁ and the experimental data. Results for the concentration dependence of the T_c show that improvements in the statistical pseudopotential approach are essential to achieve a good agreement with experiment.     

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.     

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.