The properties of liquid nitrogen

The two-electron density functions in p-space for H₂, LiH and BH are partially integrated to yield longitudinal and transverse distribution functions which, like their r-space analogues, admit of a simple physical interpretation. The forms of the corresponding one-electron distribution functions are also discussed and the identity of the longitudinal function with the directional Compton profile along the bond is noted. Finally, the effects of electron correlation are further examined by using the two-electron distribution functions to construct longitudinal and transverse hole functions in p-space.     

PRA degenerate d-band complex magnons in metallic ferromagnets at zero and finite temperatures: Inclusion of system specificity and d-electron(hole) induced charge and spin polarity fluctuations

The Barnea-Horwitz (BH) RPA nondegenerate Hubbard model (NDHM) of complex magnons in metallic ferromagnets at zero and finite temperatures is generalized to include ten-fold d-electron(hole) degeneracy using the Moriya-Kemeny-Siegel (MKS) ten-fold degenerate Hubbard model (TDHM). As such, in the RPA, Hartree-Fock (HF) one-electron(hole) regime, metallic ferromagnet specificity is automatically included via the inherent d-bandwidth (w^TB_d) and d-bandfilling (?_B) dependence of the TDHM electron(hole)-electron(hole) interaction. As such, local HF limit electron(hole) spin and charge polarity fluctuations, via the increased possibility of multiple electron(hole) site occupancy, even in the RPA-HF, are automatically included.     

On the structure of equations of optimized effective potential method

The ground-state energies of the Be atom and the H₂, LiH, BeH, and BH diatomic molecules are calculated using the optimized effective potential method.     

Edge current switch of two-dimensional electron gas using carrier density control

We have investigated the effects of electron density discontinuity on the transports of edge currents of two-dimensional electron gas (2DEG). The electric field applied to a gate, which covers the 2DEG partially, gives rise to change in the carrier density and results in a density gradient, which deforms the edge currents. The transverse and longitudinal resistances were measured as functions of gate voltage V_G in the quantum Hall regime. The deviations of the longitudinal resistances from the normal quantum Hall resistances are attributed to the reflections of the edge currents under the influence of the abrupt density discontinuity. A switching behavior of the transverse resistance by controlling the gate voltage was observed when V_G=−2.2 and −2.0 V for magnetic field H=5 and 7.2 T, respectively.     

The interpretation of binary (e, 2e) spectroscopy using spin-coupled theory

We discuss the possible interpretation of the (e, 2e) scattering technique (electron momentum spectroscopy) in terms of spin-coupled wave functions. The spin-coupled method is a modern valence bond approach which is based on a simple picture of singly occupied orbitais. In general these are highly localized, unlike their molecular orbital theory counterparts, and this has important consequences for the form of the momentum space orbitais to which the experimental differential cross-sections can be related. We compare spin-coupled and molecular orbital electron densities for individual orbitais of LiH, NH, CH₂CHF and CH₂CHCl, both in momentum space and in the more familiar position space representation. Finally, we comment briefly on the possible significance of this new approach for resolving the present discrepancies between theory and experiment for NH₃, H₂O and HF.     

Quantum Monte Carlo study of a proton in an electron gas

The polarization of jellium by a fixed proton impurity at 0 K is determined for an electron density range from metallic to dilute using the quantum Monte Carlo algorithm. Preliminary results show the correct H^– binding limit for the impurity in a dilute electron gas. The screening indicates transitions from two-to one-electron binding and from localized to delocalized electrons as the jellium density increases. The results are compared to density functional calculations. Pair distribution functions, Friedel oscillations, and binding energies are discussed.     

Analytical ab initio computation of force constants and dipole moment derivatives: LiH,Li2 and BH

Ab initio calculations of harmonic force constants and dipole moment derivatives have been performed for the diatomic molecules LiH, Li₂ and BH, using Hartree-Fock perturbation theory for a series of spherical gaussian SCF-MO wavefunctions. The results of these computations support the conclusion made in a previous paper that the so-called general method of calculation is the most reliable. The results obtained with the energetically best wavefunctions are (experimental values in parentheses, atomic units throughout): Force constants: LiH 0·071 (0·066); Li₂ 0·019 (0·016); BH 0·210 (0·196). Dipole moment derivatives: LiH - 0·48 (-0·42±0·06); BH - 0·67 (-0·4).     

On the direct determination of constrained pure state one-electron density matrices: II. A modified algorithm and its applications

An algorithm recently proposed by us for the direct determination of pure state one-electron density matrices (P) under externally imposed constraints has been remodelled. The modified algorithm is applied to the construction of ground state potential energy curve of lithium hydride molecule usingknown values of dipole moments of LiH at various internuclear distances as theexternal constraint. The equilibrium internuclear distances (R _c) is seen to be unaffected by the constraint, but the force constant improves remarkably. The relevant features of the constrained density vis-a-vis those of the unconstrained one are analyzed revealing some of the improved features of the constrained density.     

Ultrasonic-assisted synthesis of ZnTe nanostructures and their structural,electrochemical and photoelectrical properties

Colloidal zinc telluride (ZnTe) nanostructures were successfully processed through a simple and facile ultrasonic (sonochemical) treatment for photoelectronic applications. The particle-like morphological features, phase and nature of valence state of various metal ions existing in ZnTe were examined using electron and X-ray photoelectron spectroscopic tools. Raman spectroscopic measurements revealed the dominance of exciton-phonon coupling and occurrence of TeO₂ traces in ZnTe through the corresponding vibrations. Optical bandgap of the ZnTe suspension was estimated to be around 2.15 eV, authenticating the direct allowed transitions. The p-type electrical conductivity and charge carrier density of ZnTe were additionally estimated from the Bode, Nyquist and Mott-Schottky type impedance plots. The photoelectrical properties of ZnTe were investigated by fabricating p-ZnTe/n-Si heterostructures and studying their corresponding current-voltage characteristics under dark and white light illumination. The diodes revealed excellent rectifying behaviour with significant increase in reverse current under illumination. The stability of the devices were also affirmed through the time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the integrated heterojunctions. The obtained results also augment the potential of sonochemically processed ZnTe for application in photo detection and sensor related functions.     

Universal basis of two-center functions. test computations of certain diatomic molecules and ions

It is shown that the basis of two-center functions is universal. The dependence of the nuclei of atoms comprising a molecule on charges and on the intranuclear spacing is separated explicitly in the integrals used in analyzing diatomic molecules. The basis integrals constructed once permitted rapid and effective execution of computations for the ground state potential curves for a number of electron systems: H₂, He₂ ²⁺, HeH⁺, He₂, LiH, Li₂, HeB⁺, Be₂.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 74–79, November, 1986.     

Self-consistent perturbation theory

The density matrix form of Hartree-Fock perturbation theory is developed for the case in which the basis functions themselves are perturbation-dependent. Energy expressions are derived, through second order, for both single and double perturbations.

The theory is applied in the calculation of electric dipole polarizabilities and hyperpolarizabilities for atoms (He, Be) and molecules (H₂, LiH), with excellent results. The high computational efficiency of the method is discussed and possibilities of further development are outlined.     

Multicomponent Electron–Hole Liquid in Si/SiGe Quantum Wells

The density functional theory is used to calculate the energy of an electron–hole liquid in Si/Si_1–xGe_x/Si quantum wells. Three one-dimensional nonlinear Schrödinger equations for electrons and light and heavy holes are solved numerically. It is shown that, in shallow quantum wells (small x), both light and heavy holes exist in the electron–hole liquid. Upon an increase in the Ge content, a transition to a state with one type of holes occurs, with the equilibrium density of electron–hole pairs decreasing by more than a factor of 2.     

Comparisons of some molecular properties calculated with basis sets of Slater-type orbitals and floating spherical gaussian orbitals for BH3, BH4 -, B2H6, B4H4, C2H2, C2H4, C2H6, CH4, and C3H4

Some one-electron molecular properties are calculated for BH₃, BH₄ ^-, B₂H₆, B₄H₄, CH₄, C₂H₂, C₂H₄, C₂H₆, and C₃H₄. The wave functions used are constructed from minimal basis sets of STO's and FSGO's. The results obtained from the latter wave functions show that the good agreement with the STO values of the molecular energy is not always maintained with one-electron properties.     

Thin layers of gallium-arsenide: A molecular orbital study

The quasirelativistic INDO/1 method has been used to generate molecular orbitals for some {GaAs}_n clusters up to 160 atoms. On the basis of these one-electron energy levels the density of states (DOS) and density of hole functions have been calculated. Various projections of DOS functions are discussed. The calculations are compared with those generated by periodic crystal orbitals of the EHT quality and with experimental ESCA spectra on thin layers of GaAs.     

Quantum Hall effect in back-gated InAs/GaSb heterostructures under a tilted magnetic field

We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-ν_net discontinuous. Under tilted magnetic fields, these R_xx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings.     

Formation of excitons from free electron–hole pairs due to acoustic phonon interactions in quantum wells

A study of the process of exciton formation due to acoustic phonon interaction in quantum wells (QWs) is presented. Considering that excitons are formed from photoexcited free electron–hole pairs, we have derived the rate of such formation as a function of density and temperature of charge carriers and wavevectorK_|| of the center-of-mass motion of exciton, and finally applied our theory to GaAs/AlGaAs QWs. We have found that the formation of an exciton due to acoustic phonon emission is more efficient at relatively large values ofK_|| (hot excitons) whereas that due to longitudinal optical (LO) phonon emission is more efficient at relatively small values of K_||.     

Two-phonon Raman spectra of LiH and LiD crystals

The experimental two-phonon Raman spectra of LiD and LiH are reported here. A deformation dipole model formulated elsewhere for LiD is used to compute the lattice dynamics of LiD and LiH required in the Raman intensity calculations. The use of the same model for LiH is justified by the good agreement between the peak positions of the temperature-weighted two-phonon density of states and the various experimental spectra. The Raman intensity calculations are carried out by treating the second-order expansion coefficients in the polarisability tensor as adjustable parameters. The need for the parameters associated with the next-nearest-neighbor ions is clearly demonstrated for all the spectra. A single set of six parameters for the T₂₈ spectra and thirteen parameters for the E₈ (or A₁₈) spectra is found to explain all the experimental spectra of LiD and LiH quite well. Since the polarisability of Li⁺ is very small, the need for the second-neighbor positive-positive parameters reflects on the extended and highly polarisable nature of the H^? or D^? ion.     

Landau Diamagnetism,Pauli Paramagnetism,and Determination of Longitudinal and Transverse Kinetic Energy Components of a Degenerate Nonrelativistic Electron Gas

The Fermi energy, density of average kinetic energy, and average density of kinetic energy of the transverse finite motion of an electron gas of a specified concentration are calculated taking into account Landau diamagnetism and Pauli paramagnetism. The kinetic energy of a longitudinal continuous electron motion along the direction of the external magnetic field H is estimated. It is shown that the kinetic energy of the longitudinal continuous motion vanishes with increase in the external magnetic field strength in the quantum limit where the maximum Landau quantum number N _m = 0. For N _m > 0, the longitudinal kinetic energy component of a degenerate electron gas somewhat increases with magnetic field strength. The cause of the erroneous result is discussed.     

Spatial correlation of an electron and hole in quasi-two-dimensional electronic system in a strong magnetic field and its relationship to the light-scattering tensor

The spatial correlation of light-generated electrons and holes in a quasi-two-dimensional electron gas in a strong magnetic field is investigated in an approximation linear in the intensity of the exciting light. The correlation is due to the interaction of the electrons and holes with longitudinal optical (LO) phonons. The theory permits calculating, on the basis of a special diagrammatic technique, two distribution functions of an electron-hole pair with respect to the distance between the electron and the hole after the emission of N phonons: first, the function determining the total number of pairs which have emitted N phonons and, second, the function related to the rank-4 light-scattering tensor in interband resonance Raman scattering of light. A special feature of the system is that the electron and hole energy levels are discrete. The calculation is performed for a square quantum well with infinitely high barriers. The distribution function and the total number of electron-hole pairs before the emission of phonons as well as the distribution function corresponding to two-phonon resonance Raman scattering are calculated. The theory predicts the appearance of several close-lying peaks in the excitation spectrum under resonance conditions. The number of peaks is related to the number of the Landau level participating in the optical transition. The distance between peaks is determined by the electron-phonon coupling constant. Far from resonance there is one peak, which is much weaker than the peaks obtained under resonance conditions. Zh. éksp. Teor. Fiz. 111, 2194–2214 (June 1997)     

Electron pairs for HTSC

A simple physical picture of superconductivity is proposed for extremely doped CuO₂ planes. It possesses features that are observed for HTSC, such as a high superconducting transition temperature, $d_{x^2 - y^2 } $ the symmetry of order parameter, and the coexistence of a one-electron Fermi surface and the Bose-Einstein condensate of preformed electron pairs.