Self-consistent State Research Articles

Self-consistent antiferromagnetic ground state for La2CuO4 via energy-band theory.

We have used the pseudofunction method to compute self-consistent spin-polarized energy bands for ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. The ground state is found to be semiconducting and antiferromagnetic (AF) with a moment of 0.35${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. The net moment resulting from the occupation of 82 itinerant bands is localized on the Cu atoms only. Our results agree with experiments in which ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ is found to be semiconducting and AF with a moment on the Cu atoms of (0.35\ifmmode\pm\else\textpm\fi{}0.05)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ (neutron scattering) or in the range 0.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ to 0.6${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ (muon-spin resonance). Sr is found to produce holes on the out of plane O contrary to the assumption used in many strong-correlation theories of superconductivity.

Collective excitations in a doped antiferromagnet.

We develop a systematic procedure for studying a doped antiferromagnet in the intermediate-coupling regime. Starting with the Hartree-Fock (HF) solution to the Hubbard model in the half-filled-band case, we obtain the spin-wave spectrum and find that in the strong-coupling limit the spin-wave mode is identical to that obtained from the corresponding spin-(1/2 Heisenberg model. We self-consistently evaluate the one-loop correction to the sublattice magnetization due to spin-wave excitations and in the U/t\ensuremath{\rightarrow}\ensuremath{\infty} limit find that the sublattice magnetization is reduced to 0.6, i.e., to 60% of its HF or saturation value. As a first step toward applying this systematic procedure to a doped antiferromagnetic, we numerically study in detail the HF ground state with few holes, which become self-consistently trapped by the self-induced spin polarization, resulting in the spin-bag ground state. We find that for U/t<20 the transverse terms in the HF Hamiltonian iterate toward zero. We examine the nature of collective excitations in the spin-bag ground state in a 10\ifmmode\times\else\texttimes\fi{}10 lattice system for U/t=5, which is representative of the intermediate-coupling regime. We explicitly show that the spin-bag state admits to a stable Goldstone mode, confirming the local stability of this HF state. We analytically examine the self-consistent HF state, obtained in the rigid-band approximation, of a system with finite hole density. We find that, although self-consistent, this HF state is unstable with respect to collective excitations toward the formation of a two-dimensional incommensurate structure with a wave vector proportional to the linear hole density.

Self-consistent spherical accretion shocks around black holes

The radiation shock dynamics of an accreting black hole is modeled, including nonadiabatic radiative losses and gains, heat transport processes, and pair processes in a simplified treatment. In the case of low specific angular momentum, self-consistent steady state solutions with shocks can exist in a spherical accretion flow, which for moderately supercritical accretion rates lead to radiation efficiencies of the order 0.01 and luminosities of the order 0.1 times the Eddington luminosity. To take a specific example, if the mass accretion rate is three times the critical rate, then the shock zone begins at about 80 Schwarzschild radii. The resulting luminosity, seen at infinity, is L(Edd)/20 and therefore, the efficiency is 10 to the -1.8. The positron density in the shock zone is about 20 percent of the protron density, and the Thompson optical depth of the zone is about 3. The temperature of the outgoing radiation is about 0.1 MeV. This mechanism is relevant for quasar and AGN models located in elliptical galaxies. 27 refs.

Self-consistent antiferromagnetic ground state for La2CuO4 and CuO via energy band theory

We have used the pseudofunction (PSF) method to compute self-consistent spin- polarized energy bands for La2CuO4 and CuO. The ground state is found to be semiconducting and anti-ferromagnetic (AF) for both La2CuO4 and CuO. For La2CuO4 the Cu moment is 0.35μB. For CuO, the moment is 0.68 μB on the Cu site and 0.19 μB on the O site. The moments are in agreement with neutron diffraction data.

Physical picture of electron correlations in three-center four-electron bonds

It is shown that the strong electron correlations of π electrons in the O3 molecule may be well understood in terms of a simple analytic model which is a natural extension of a bond orbital approximation to the case of a three-center bond. Electron correlations are here responsible for the increase of density at the central atom and for enhanced correlations at both terminal ones. This result is confirmed by a numerical calculation of the interatomic correlations by using a local ansatz imposed on a semiempirical selfconsistent field ground state. It is argued that the discussed increase of the bond polarity in the O3 molecule is a universal phenomenon for three-center bonds filled (on the average) by more than one electron per atom, as, for example within the CuO2 planes of Cu based perovskites.

P-wave pion scattering in the Los Alamos soliton model.

P-wave pion-nucleon scattering at low and intermediate energies has been calculated in the Los Alamos soliton model that describes the nucleon as a self-consistent soliton state of a dynamic QCD bag or core interacting with its pion field. The P-wave phase shifts in the 11 and 33 channels and the inelasticity in the 11 channel are computed within the subspace consisting of at most one physical pion plus one of three soliton states of the dynamic bag or core with its pion field. The soliton states used in the calculation are computed within an approximation that treats only pionic excitations of the self-consistent nontopological soliton ground state corresponding to the nucleon and neglects excited states of the core motion. Within this approximation, the soliton states used are the model's lowest two 11 states and lowest 33 state; these states can be thought of as the nucleon, Roper, and \ensuremath{\Delta} states, where the latter two are in first approximation discrete states in the continuum. The coupling of the excited states to the continuum states gives the states a width in the usual way. The position of the 33 resonance is found to be sensitive to the value of the bag or core radius. The present approximate description of the scattering does not give a resonance in the 11 channel. The implications of these results for future work on the soliton model are discussed.

Ab initio calculation of the energy and structure of solids

We review ab initio methods for calculating the energy and structure of solids based on density functional theory and pseudopotentials, and illustrate some of their recent successes. The ideas of Car and Parrinello for finding the fully relaxed self-consistent ground state are then discussed. Some problems that arise in applying these ideas to metals are pointed out, and a way of overcoming them is outlined. It is shown how the new techniques can be used to calculate the formation energy of the vacancy in simple metals, and results for the case of aluminium are summarized. Some remarks on the use of these techniques for defects in transition metals are offered.

Intersubband resonances and plasmons in quasi-two-dimensional systems: A line-shape and coupling analysis.

Charge- and spin-density fluctuation spectra, as they appear in electron scattering and optical experiments, have been calculated for accumulation layers at n-type GaAs interfaces. Starting with a self-consistent ground state, we employ the random-phase approximation to evaluate the nonlocal susceptibility of the anisotropic electron system. Temperature effects and excitations to the continuum of states are also included in the theory. Profiles of the complex induced potential inside the quasi-two-dimensional (2D) electron gas reveal the internal structure of the collective modes. We find substantial deviations of the 2D plasmon dispersion from strictly two-dimensional theories. Both nonlocality and coupling between the subbands play a role. Also the dispersion of the intersubband resonance has been calculated over a wide range of wave vectors ${q}_{?}$ and for various electron densities. The well-known depolarization shift at small ${q}_{?}$ is strongly influenced by the spectral proximity of the continuum of states.

Effects of core motion on the nucleon electric form factors.

When the nucleon is described as the self-consistent nontopological soliton ground state of a translation-invariant model Hamiltonian for a nonstatic baglike core interacting with a pion field, the motion of the core is shown to have a significant effect on the proton and neutron electric form factors, as compared to previous cloudy-bag-model (CBM) calculations that neglect the core motion and treat the baglike core as a static source of pion field. In the translation-invariant model, the charge density of the nucleon has contributions from the core and from the pion cloud, as in the usual static CBM; in addition, and in contrast to the usual static CBM, there are effects due to the spreading of the core charge density as a result of the self-consistent motion of the core within the pion field that it generates. The spreading of the core density tends to weaken the core-pion interaction for a fixed bag radius so that the binding of the core-pion system is less than in the static cloudy bag. Hence, the motion of the core softens the electric form factors as compared to static CBM calculations.

Effects of core motion on static properties of the nucleon.

The effects of core motion in the nucleon are calculated in a simple model in which the translation-invariant Hamiltonian describes a pion field interacting with a nucleon core. The ground state of the system is shown to be a self-consistent state in which the pion field binds the core, which, in turn, acts as an effective nonstatic source of the pion field. The form factor of the nonstatic source is softer than the intrinsic form factor of the corresponding Hamiltonian without core motion. The effects of core motion on the nucleon magnetic moments and charge radii are presented for the case that the core properties are computed in the bag model. It is found that for a given set of observed properties, the bag with core motion is smaller than the corresponding bag without core motion.

Hybridization effect in superconductors

We study the hybridization effect in the superconducting phase of a two band system. Assuming the stabilization of intra- and interband Cooper pairs, one shows that the hybridization changes the self-consistent bound state energy of the two-particle state. Numerical results are obtained in a simple case.

Theory of self-consistent optical nutation

5, 6. L. D. Landau and E. M. Lifshitz, The Classical Theory of Fields, Pergamon (1976). V. P. Silin and A. A. Rukhadze, Electromagnetic Properties of a Plasma and Plasmalike Media [in Russian], Atomizdat, Moscow (1961), Paragraph 12. THEORY OF SELF-CONSISTENT OPTICAL NUTATION V. V~ Kocharovskii and VI. V. Kocharovskii UDC 535.14:530.182 The features of self-consistent optical nutation are considered - coherent field oscillations, polarization, and population differences of a two-level medium in a resonator. Field frequency modulation, which changes the char- acteristics of nutation and is significant along with amplitude modulations, is also taken into account. This results in beats for electromagnetic and polariton "hot" modes with differing amplitudes in a resonator filled with a two-level medium. A nonnutational, self-consistent state for the uninverted medium and field is shown to exist. It is found that, in the presence of field dissipation, the process of optical nutation transforms into a state of superabsorption (an irreversible process of cooperative spontaneous relaxa- tion). !. Introduction Optical nutation is a coherent, nonsteady-state process of slow oscillation in the popula- tion difference AN = N2 - NI and in the complex polarization amplitude P of a two-level medium acted upon by an electromagnetic field in a resonator. In the approximation of a resonant, monochromatic field with an amplitude E and a frequency m = ~0, nutation is described by the oscillator solution of Rabi [i-3] with a characteristic frequency ~R = d[E[/h (d is the di- pole moment of a two-level optical transition at a frequency ~0). For a sufficiently high concentration N of two-level molecules, one must consider the reverse effect of the medium on the field, i.e., the cooperative interaction of the molecules by means of the electromag- netic field. The latter is significant if the cooperative frequency of the medium ~c, deter- mined by the relation

Radiative properties of puffed-gas mixtures

The radiative yield of dense, high-temperature plasma mixtures has been studied theoretically for conditions typically attained in puffed-gas implosions from high-voltage pulse power generators. The mixtures are characterized using an equilibrium ionization/radiation model which calculates the self-consistent state density populations of detailed level configurations by solving the complete set of atomic rate equations. In order to accurately model the quantitative line emission as well as the radiation spectrum from the plasma mixtures, detailed atomic models of L- and K-shell ion level structure and collisional processes in neon, argon, and krypton are employed; these models are described in detail. Specific mixtures reported on include neon/argon, argon/krypton, helium/argon, and helium/krypton. They are considered as compressed stationary plasmas, radiating at constant temperature and density (the time-history of the implosion dynamics is neglected in this report). While no power amplification is detected in the optically thin approximation via the various mixtures, broadband spectral enhancement is demonstrated using various constituents.

Two-state system coupled to a boson mode: Quantum dynamics and classical approximations

The relation between classical and quantum mechanical integrability is investigated for a boson mode coupled to a two-level system. Different semi-classical approximations of this system are considered which are obtained by (i) factorization of expectation values of the two-state variable and the boson, (ii) making a WKB-type approximation, (iii) replacing the boson by a classical field of constant amplitude and fixed frequency and (iv) putting the boson into a self-consistent coherent state. The results vary considerably and include cases of non-integrable and integrable classical dynamics. Quantum mechanically the system is found to satisfy a criterion of quantum mechanical integrability, which we formulate, but the separated Hamiltonian of the boson alone does not have a well-defined classical limit. Numerical results for the energy spectrum and expectation values are obtained, which show a high degree of regularity but also display overlapping avoided crossings usually associated with non-integrable Hamiltonians. The exact dynamics of the occupation probabilities of the two levels is also analysed numerically. The dependence of quantum mechanical recurrence effects (in quantum optics known as revivals) on coupling strength, frequency detuning and initial conditions is studied. The revivals are found to disappear in the case of strong coupling. The Fourier spectra of the dynamical expectation values are also calculated

Ponderomotive effects in nonneutral plasmas

The ponderomotive effects which arise in a single species plasma, i.e., a nonneutral plasma, are considered. The important difference from a neutral plasma is that quasineutral density cavities given by δn/n0≂−‖E‖2/16πn0T cannot arise in a single species plasma. Instead, it is found that the ponderomotive force is balanced by self-consistent space charge fields, and results in δn≂∇2‖E∥‖2/16πmω2, where ω is the frequency and E∥ refers to the wave electric field parallel to the confining magnetic field. In addition to the density rearrangement, the zero order E×B rotation is modified. The self-consistent nonlinear state has been found for a large-amplitude l=0 axially standing Gould–Trivelpiece wave. The linear dispersion relation is modified by the presence of the large-amplitude wave and results in a nonlinear frequency shift. This shift produces an interesting hysteresis effect in the nonlinear resonant response of the plasma when the frequency of the external driver is swept slowly.

On the nonlinear theory of surface wave generation in an electron beam-plasma system

The nonlinear interaction of a relativistic charged beam with the surface wave excited when the beam slides along a plasma layer is considered. The self-consistent nonlinear state of the wave-beam system has been analyzed on the basis of the Maxwell and kinetic equations. The saturation amplitude, wave-phase velocity, the wave generation efficiency, and other quantities have been obtained as a function of the initial parameters of the system.

Theoretical studies of hydrogen interstitials in AB 2 structure laves phase compounds

In experiments by Peretz et al. on the pseudobinary system Zr(V x −Co 1− x)in2 , an order-of-magnitude increase has been found in the hydrogen affinity at the vanadium-rich end compared with that at the cobalt-rich end. Didisheim et al. have identified the tetrahedral interstitial sites as the positions at which hydrogen (or deuterium) atoms are located. To investigate the hydrogen storage behavior in these compounds we have used the results of self-consistent augmented plane wave calculations for ZrV 2 and ZrCo 2 as the basis for a muffin tin Green's function study of dilute hydrogen impurities. We provide an evaluation of the applicability of this method (with suitable generalization) to the hydrides of Laves phases and discuss the self-consistent defect charge and state densities and their implications for bonding in these systems.

Nonlinear wave-beam interaction in plasma waveguide systems (asymptotic estimates)

The resultant (asymptotically equilibrium state) of relativistic electron beam and a electromagnetic wave in plasma waveguide in the case when the wave is purely harmonic is studied. Analysing the self-consistent nonlinear state of the wave-beam system on the basis of Maxwell and Vlassov equations and the balance of momentum and energy, a number of new analytical evaluations have been obtained. These estimates refer to the characterization of the trapping of the particles, the beam 'temperature', the field amplitude and energy, the redistributions of the beam kinetic energy and the dependence of the generation efficiency on parameters of the system.

Fluctunoic states of electrons in ferroelectrics-semiconductors and ferro-semiconducting solid solutions

Abstract The fluctuonic states of electrons in ferrosemiconducting crystals and their solid solutions are considered using the modified landau-ginburg-Devonshire theory that gives the following results. 1. The functional is obtained which describes the self-consistent state of polarization fluctuation and wave function of the polarizing electron. The dimensionless varibles are used. The task decision is considered for the finite depath spherical pit-type potenitial through the parametric potential. The numerical calculations of thee main charcteristiecs of phasons (radius, polarazation, full energy, energyof localized electron, density of surface energy et al.) depending on temperature are carried out the stabiliity conditions and the temperature range of phason existence are considered. 2. Some anomalous photogerroelectric phenomena (photorefractive efffect, photoinduced Rayleigh scattering, luminescence et al.) are considered. The calculation of these effects for BaTio3 is carried out basing on the phas...

Very narrow quasi elastic scattering in BaTiO3 close to the phase transition

An excess electron in a first order phase transition ferroelectric material (e.g. BaTiO3) produces a local change in the spontaneous polarization: it can result in the creation of a new self-consistent state (phason). The phason states and the photoferroelectric phenomena can exist simultaneously if the initial free electron is the result of an optical excitation. The connection between the concept of photofluctuation (introduced for the explanation of the photoinduced Rayleigh scattering and of the photovoltaic effect) and the phason state is discussed. The calculations are restricted to the non degenerate case for the electrons; we consider also that the phasons are not quasiparticles.