A model pseudopotential calculation of the electronic structure of Si (111)-1 × 1 surface

We report a model pseudopotential calculation of the electronic structure of Si (111)-1 × 1 unrelaxed, relaxed and expanded surfaces. It is shown that our results for the surface states on these faces are in good agreement with results from other self-consistent pseudopotential and semi-empirical tight-binding calculations.     

Solid in the kicking laser field

The band structure problem of a solid in the laser field is investigated. One-dimensional Kronig-Penney model is chosen as an ideal crystalline solid model and the influence of the laser field is modeled by a train of periodic δ-kick pulses. Then, the realistic approach for simple solid on the basis of the experienced pseudopotential theory is given and the previous results are confirmed: The evaluated spectrum displays little sensitivity of the laser-perturbed band structure to the oncoming field. This gives credence to the conjecture that the spectrum is dense in the relevant region of the first quasienergy zone. The band structure retain practically unaltered. In addition the optical conductivity of sodium in the kicking field is calculated. The appropriate theoretical investigations can be relevant for practical realization purposes. The solids can be almost transparent under kicking pulses.     

Models of Two-Level Atoms in Quasiperiodic External Fields

We prove that the spectrum of the generalized quasienergy operator of a plane-polarized two-level atom in a strong external quasiperiodic electromagnetic field with nonzero constant Fourier component is pure point, under Diophantine conditions on the frequency ratio, and excluding a small subset of resonant values. The widespread belief that there may be only pure point spectrum in such models is briefly discussed in Section 2 and the circularly polarized case—a well-known soluble model—is revisited from the point of view of the quasienergy operator..     

Unified theory of static,dynamic, and electronic properties of aluminium

The problem of including the many-electron interactions into a pseudopotential theory of aluminium is re-considered. It is shown that due to the valence-core exchange and correlation, the pseudopotential is necessarily non-linear in the valence-electron charge density. We propose a simple way to account for this non-linear effect. This improved valence-core exchange potential allows to give a unified theory of static, dynamic, and electronic properties of aluminium.     

Two-level system in the field of two intense waves

The problem of a two-level system in the field of two intense monochromatic waves is reduced to the problem of a two-level system in the field of a nonmonochromatic but periodic (in time) wave, which makes it possible to introduce quasienergy states. An investigation is made by the method proposed in [1, 2]. For the quasienergy an analytic expression is obtained that is valid in the complete range of variation of the frequencies at all values of one of the intensity parameters and moderate values of the other. The quasienergy is also calculated in the case of asymptotically large values of the parameters of both intensities when one of the frequencies of the external field is equal to the resonance frequency. The Fourier components of the density matrix at the frequencies of the external field are also calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 23–25, August, 1980.We thank M. L. Ter-Mikaelyan for interest in the work.     

The ground and low-lying excited potential curves of SO

A method is presented for approximating the effect of core electrons by a pseudopotential which is an extension of one previously presented by Dixon and Hugo. The pseudopotential is constructed in a fully ab initio manner from atomic SCF calculations. It is non-local in both radial and angular coordinates, but its matrix elements are none the less easy to evaluate. The method has been implemented within a multi-structure valence-bond framework. The approximations arising from the use of finite basis sets, both for the pseudopotential and for the valence wavefunction, inevitably lead to errors in calculated energies. However, these errors are largely atomic in origin. Thus, in addition to ab initio calculations we also use empirical atomsin-molecules corrections to minimize both basis set errors and atomic correlation errors. These method are applied to potential curves for 21 electronic states of the SO molecule. Comparison is made of the curves calculated using the ab initio multi-structure valence-bond method without and with the atoms-in-molecules corrections. The potential energy curves of three, previously unobserved, bound electronic states of SO are calculated. We estimate that these states, ¹Σ^-, ³Δ and ³Σ⁺, lie in the region of 3·2 to 3·4 eV above the ground state.     

Quasiparticle lifetimes due to A1 impurities in Zn

We have calculated the quasiparticle lifetimes due to Al impurities in Zn. For the Zn electronic structure we use the wave functions, Fermi velocities and surface elements calculated by Tomlinson and Swihart who based their work on the accurate pseudopotential fit to the de Haas-van Alphen data obtained by Stark and Falicov. The impurity pseudopotential form factor is obtained from the procedure developed by Shaw.     

Electronic interactions in the expanded metal compound Li-NH3

Inelastic x-ray scattering was used to measure the plasmon as a function of electron density in liquid lithium ammonia as well as the low temperature solid phase. As the electronic density is lowered, electronic correlation effects cause the random-phase approximation (RPA) to break down, requiring more advanced theoretical treatments. The deviation from RPA becomes greatest at the lowest electronic densities. We also see evidence for decreased electronic screening as shown by an increase in the strength of the pseudopotential at lower concentrations. Plasmon behavior in the solid is similar to that of the heavier alkali metals, but surprisingly different than in the liquid.     

Total electronic energy of a noble metal ordered alloy in the pseudopotential method

Application of the pseudopotential method to noble metal ordered alloys is considered in this paper. Expressions are obtained for the Fourier components of the crystal potential and for the total electronic energy of the alloy. The pseudopotential matrix elements are factorized, and the possibility of transforming to a pair interaction representation is shown. Expressions are obtained for the pair potential of indirect interionic interactions in a noble metal binary ordered alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 21–28, August, 1973.     

Calculation of the residual resistivity based on multiple-plane-waves and iterative solutions to the Boltzmann equation: Application to aluminium alloys

We describe a multiple-plane-wave pseudopotential calculation for the residual resistivity in alloys. The electronic wavefunctions, the Fermi surface, and the scattering rates are all determined from a 4-OPW calculation, while the mean free path is determined from an iterative technique which is developed for solving the Boltzmann equation. Numerical results obtained for Al alloys reveal that in many cases the OPW-mixing leads to dramatic enhancement of the residual resistivity over the free electron value, and that this enhancement improves agreement with experiment.     

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.     

Nonlocal pseudopotentials and magnetic fields

We show how to describe the coupling of electrons to nonuniform magnetic fields in the framework of the widely used norm-conserving pseudopotential approximation for electronic structure calculations. Our derivation applies to magnetic fields that are smooth on the scale of the core region. The method is validated by application to the calculation of the magnetic susceptibility of molecules within density functional theory (DFT) in the local density approximation. Our results are compared with high-quality all-electron DFT results obtained using Gaussian basis sets and another recently proposed pseudopotential formalism.     

Electronic structure of graphite-like and rhombohedral boron nitride

The electronic spectra of the valence and conduction bands of the hexagonal graphite-like h-BN and rhombohedral r-BN modifications of boron nitride are presented. The electronic structures are calculated by the pseudopotential technique with an auxiliary parameter introduced which takes into account anisotropy of the crystal pseudopotential; the parameter is chosen to ensure agreement with the optical data for h-BN. The electronic structures of both modifications are qualitatively similar but differ slightly (up to 0.2 eV) with respect to interband energies. Both modifications are indirect-band dielectrics with minimal indirect and direct band gaps of 4.65 and 5.27 eV, respectively, for h-BN amd 4.8 and 5.5 eV for r-BN. The anisotropy of the electronic structure and its possible alterations on intercalation of the BN lattice with carbon are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 27–32, February, 1992.     

Magnetic properties of Pd atomic clusters from different theoretical approaches

We report a comparative study of the magnetic properties of free-standing Pd_N clusters (2 ≤N ≤21) obtained through two different theoretical approaches that are extensively employed in electronic structure calculations: a semi-empirical Tight-Binding (TB) model and an ab-initio DFT pseudopotential model. Conclusions are drawn about the reliability of the TB model for the investigation of the electronic structure and magnetic properties of such complex 4d Transition Metals (TM) systems and we compare the results with previous systematic DFT calculations and comment on some available experiments in the literature.     

First-principles study of interface relaxation effect on interface and electronic structures of InAs/GaSb superlattices with different interface types

We have implemented first-principles relativistic pseudopotential calculations within general gradient approximation to investigate the structural and electronic properties of quaternary InAs/GaSb superlattices with an InSb or GaAs type of interface. Because of the complexity and low symmetry of the quaternary interfaces, the interface energy and strain in the InAs/GaSb superlattice system have been calculated to determine the equilibrium interface structural parameters. The band structures of InAs/GaSb superlattices with InSb and GaAs interfaces have been calculated with respect to the lattice constant and atomic position relaxations of the superlattice interfaces. The calculation of the relativistic Hartree–Fock pseudopotential in local density approximation has also been performed to verify the calculated band structure results that have been predicted in other empirical theories. The calculated band structures of InAs/GaSb superlattices with different types of interface (InSb or GaAs) have been systematically compared. We find that the virtual–crystal approximation fails to properly describe the quaternary InAs/GaSb superlattice system, and the chemical bonding and ionicity of anion atoms are essential in determining the interface and electronic structures of InAs/GaSb superlattice system.     

A pseudopotential based theory of the driving forces for electromigration in metals

We present a pseudopotential calculation of the driving forces for atomic migration in metals in the presence of electron currents. When electrons are scattered by impurities in a metal, we find that a force is generally exerted on each atom in the vicinity of the scattering center. Because the scattering is predominantly elastic, it is possible to express this force field as the classical electrostatic force arising from the total electronic charge, as has been assumed by Friedel and Bosvieux. The electron charge density is determined from a pseudopotential calculation, and the resulting force is expressed as a sum of effective interactions between the diffusing atom and all crystal defects.The forces on an atom arising from the electron scattering and from the applied electric field together comprise the driving force which causes a net current of atoms. The driving forces are calculated for intestitial and vacancy migration in several metals, and the results are found to compare favorably with most experimental data.     

Quantum-mechanical interatomic potentials with electron temperature for strong-coupling transition metals

In narrow d-band transition metals, electron temperature T(el) can impact the underlying electronic structure for temperatures near and above melt, strongly coupling the ion- and electron-thermal degrees of freedom and producing T(el)-dependent interatomic forces. Starting from the Mermin formulation of density functional theory, we have extended first-principles generalized pseudopotential theory to finite electron temperature and then developed efficient T(el)-dependent model generalized pseudopotential theory interatomic potentials for a Mo prototype. Unlike potentials based on the T(el)=0 electronic structure, the T(el)-dependent model generalized pseudopotential theory potentials yield a high-pressure Mo melt curve consistent with density functional theory quantum simulations, as well as with dynamic experiments, and also support a rich polymorphism in the high-(T,P) phase diagram.     

The Geometric Phases and Quasienergy Spectral Series of a Hartree-Type Equation with a Quadratic Potential

Based on the ideology of the complex WKB–Maslov method, the general construction of quasiclassically concentrated solutions is given for Hartree-type equations with a quadratic potential and periodic coefficients. Exact expressions are constructed for the quasienergies and associated quasienergy states. In the construction of solutions, an important role is played by the Hamilton–Ehrenfest system of equations obtained in this work. Explicit expressions are found for the geometric phase of Aharonov–Anandan quasienergy states.