Self-consistent calculations of hypernuclear properties with the Skyrme interaction

An extension of the Skyrme-Hartree-Fock formalism is proposed for calculating Λ binding energies (B_Λ) in hypernuclei throughout the periodic table. The calculation includes the self-consistent nuclear polarization by the Λ hyperon. Realistic estimates for ground state B_Λ's are obtained with a simple effective ΛN force and are compared with a Λ-nucleus potential model. The Λ particle excitation spectra have also been calculated. They are discussed in the context of strangeness analog state formation and the emphasis is put on the symmetry between Λ and nuclear states.     

Unitary transformation treatment of a single hole in an Ising antiferromagnet

The behavior of a single hole in a two-dimensional Ising antiferromagnet (t-J ^z model), is studied in the generalized Dyson-Maleev representation, where the spins are mapped on boson operators and the hole is described as a spinless fermion. The formal similarity with Fröhlich's polaron Hamiltonian suggests that thet-J ^z model can be approximately diagonalized by means of two successive unitary transformations, analogous to those used by Lee, Low, and Pines in their intermediate-coupling treatment of the polaron. Our approach yields an upper bound to the exact ground state energy, as well as the corresponding ground state eigenvector. Fork=0 our energy bound is remarkably close to the result of the self-consistent Born approximation over a wide range of the coupling parameter, which includes the range typically assumed for the high-T _c materials. The ground state eigenvector is used to calculate the spatial distribution of bosons (spin deviations) surrounding the hole. Here our results are qualitatively very similar to those obtained in previous work, showing that our ground state eigenvector accounts quite well for the small size of the “spin polaron” in thet-J ^z model.     

The use of scaled moments of inertia for structural calculations

A procedure for obtaining molecular structural parameters from microwave spectral data is described. The method uses the same set of experimental ground state moments of inertia used for a substitution structure determination, but is based upon a least-squares fit of moments which are obtained by scaling the experimental I₀ values. The scaling is performed in such a way that the resulting moments of inertia, I_m^γ are comparable to Watson's I_m moments and are thus close to the equilibrium moments. Initial tests and evaluation suggest that the method may lead to structural parameters which are better approximations to the r_e structure than those obtained by the conventional r₀ or r_s methods.     

Ferromagnetism in Hubbard model in many-electron operator representation

The Hubbard model for a metal with strong correlations is considered in the representation of many-electron X-operators. General self-consistent expressions are obtained for the one-particle Green function taking into account fluctuation corrections. The stability regions of the saturated and unsaturated ferromagnetism in the ground state on the n-U plane (n is the electron concentration and U is the Coulomb interaction parameter) are determined for various bare densities of states (semi-elliptic band and the square, cubic, and hypercubic lattices).     

Ionization energies and optical spectra of 5d-metal hexafluorides as calculated in the Dirac-Slater model

A relativistic self-consistent Dirac-Slater model has been used in a study of the electronic structure of 5d-metal hexafluorides. Experimental absorption spectra have been compared with calculated energies obtained as one-electron energy differences. The calculated “crystal field” splitting between the relativistic analog oft _2g ande _g levels, as well as spinorbit splitting of thet _2g level, has been found to be in good agreement with experimental data. Ionization energies which agree well with available spectra have been calculated using a transition state procedure. From a Mulliken population analysis of the molecular levels and ground state charge densities the validity of the classical crystal-field model is discussed.     

Finite-size scaling from the self-consistent theory of localization

Accepting the validity of Vollhardt and Wölfle’s self-consistent theory of localization, we derive the finite-size scaling procedure used for studying the critical behavior in the d-dimensional case and based on the consideration of auxiliary quasi-1D systems. The obtained scaling functions for d = 2 and d = 3 are in good agreement with numerical results: it signifies the absence of substantial contradictions with the Vollhardt and Wölfle theory on the level of raw data. The results ν = 1.3–1.6, usually obtained at d = 3 for the critical exponentν of the correlation length, are explained by the fact that dependence L + L ₀ with L ₀ > 0 (L is the transversal size of the system) is interpreted as L ^1/ν with ν > 1. The modified scaling relations are derived for dimensions d ≥ 4; this demonstrates the incorrectness of the conventional treatment of data for d = 4 and d = 5, but establishes the constructive procedure for such a treatment. The consequences for other finite-size scaling variants are discussed.     

Landau fragmentation and deformation effects in dipoSe response of sodium clusters

Recent experimental data on the dipole plasmon in axial sodium clusters Na _N ⁺ with 11 ≤ N ≤ 57 are analyzed within a self-consistent separable random-phase approximation (SRPA) based on the deformed Konh-Sham functional. Good agreement with the data is achieved. The calculations show that, while in light clusters plasmon properties (gross structure and width) are determined mainly by deformation splitting, in medium clusters with N τ 50 the Landau fragmentation becomes decisive. Moreover, in medium clusters shape isomers come to play with contributions to the plasmon comparable with the ground state one. As a result, commonly used methods of the experimental analysis of cluster deformation become useless and correct treatment of cluster shape requires microscopic calculations.     

Jordan-Wigner approach to the frustrated spin one-half XXZ chain

The Jordan-Wigner transformation is applied to study the ground state properties and dimerization transition in the J₁-J₂ XXZ chain. We consider different solutions of the mean-field approximation for the transformed Hamiltonian. Ground state energy and the static structure factor are compared with complementary exact diagonalization and good agreement is found near the limit of the Majumdar-Ghosh model. Furthermore, the ground state phase diagram is discussed within the mean-field theory. In particular, we show that an incommensurate ground state is absent for large J₂ in a fully self-consistent mean-field analysis.     

Analysis of ν2 of H2Se

The infrared absorption spectrum of ν₂ of H₂Se in the region from 885 to 1347 cm^?1 was obtained with a resolution limit of 0.025 cm^?1 on the University of Denver 50-cm FTIR spectrometer system. We have assigned 1604 lines for the six isotopomers of H₂Se, including 25 lines for the H₂⁷⁴Se isotopomer, and have analyzed them using Watson's A-reduced Hamiltonian in the I^r rotational representation. Ground state constants for each of the five most abundant isotopomers were obtained from fits of microwave transitions combined with weighted averaged ground state combination differences formed from the infrared bands (010), (020), (100), and (001). Upper state constants for each of the five most abundant isotopomers were obtained from least-squares fits of the spectral lines of ν₂, keeping the ground state constants fixed to the values determined from our ground state fits. An alternate set of ground state constants together with isotopic mass adjustment constants for all six isotopomers was determined by simultaneously fitting all available microwave transitions and infrared ground state combination differences. Keeping this set of ground state constants fixed, a single set of upper state constants and isotopic mass adjustment constants for the ν₂ band was determined by a simultaneous fit of infrared spectral lines from all six isotopomers.     

Accurate ab initio potential of CO(XΣ) at low cost via correlation scaling and extrapolation method

The potential energy curve (PEC) for the ground state of CO(X¹Σ⁺) has been investigated by the highly accurate valence internally contracted multi-reference configuration interaction with the Davidson correction (MRCI+Q) method in combination with a series of correlation-consistent basis sets of Dunning and co-workers. The scheme proposed by Varandas, which enables high-quality molecular potentials to be obtained from small basis set calculations via scaling and extrapolation of the electron correlation to the complete basis set limit plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field energy, has been applied to the system under consideration here. The present results are compared with the other theoretical and experimental data, and show that the present methods are credible and accurate.     

A self-consistent mean-field study of Z = 120 nuclei and α-decay chains of 292,298,299,300,304120 isotopes

A self-consistent mean-field investigation is done to test the model accuracy, model dependence, and the dependence on different model parameters in the study of superheavy nuclei. This is done within the self-consistent mean-field models-the Skyrme-Hartree-Fock-Bogoliubov (HFB), and the Relativistic-Hartree-Bogoliubov (RHB) with density-dependent couplings. A systematic comparison is made with experimental data, as well as with the macro-microscopic Finite Range Droplet Model(FRDM). The bulk ground state properties and the microscopic structure of Z=120 superheavy nuclei are investigated. Further investigation is made of α-decay series for the five isotopes ^{292,298,299,300,304}120 of Z=120 nuclei. A spontaneous fission investigation is done to account the number of α-decay before spontaneous fission starts. The experimental data available for α-decay energies and half-lives are produced reasonably. The RHB model with NL3* parameter set, and with ImSahu and UNIV2 formula to calculate the α-decay half-lives is found to be the best suited for accurately predicting the ground state properties and the α-decay half-lives of the superheavy nuclei.     

First-principles linear muffin-tin orbital investigations in the electronic and magnetic structures of double perovskites Ba2TMoO6 (T=V,Cr, Mn,Fe and Co)

The electronic and magnetic structures of ordered double perovskites Ba₂TMoO₆ (T=V, Cr, Mn, Fe and Co) are systematically investigated by means of the first-principle linear muffin-tin orbitals with the atomic-sphere approximation (LMTO-ASA) method. The calculations are performed by using the both local spin density approximation (LSDA) and the LSDA+U Coulomb interaction schemes. The results show a half-metallic ferrimagnetic ground states for T=Cr, Fe and Co in LSDA+U treatment, whereas half-metallic ferromagnetic character is observed for T=V. For T=Mn, insulating ground state is obtained, stabilized in the antiferromagnetic state. The LSDA+U calculations yield better agreement with the theoretical and the experimental results than do the LSDA.     

Interrelation of the spin,orbital, and charge degrees of freedom in half-doped manganites

Based on the double-exchange model in the tight-binding approximation, self-consistent energy-band-structure calculations are carried out for the first time for the orbital and charge ordering in La_0.5Ca_0.5MnO₃-type manganites with 16 Mn ions in the unit cell under the assumption of a linear dependence of the Jahn-Teller splitting of the e _g level on the occupancy of each ion. The equilibrium magnetic and orbital configurations are determined by minimizing the total energy with respect to the direction of the local magnetic moments and the orbital states of the Mn ions. The dependence of the splitting on the occupancy favors the stabilization of phases with charge separation. This separation is an important factor determining the magnetic structure of the ground state. The ground state can be an insulating antiferromagnetic structure of the CE or G type or a new ferrimagnetic structure with a magnetization lower than that of a saturated ferromagnet by a factor of 2. The existence and the width of the bandgap in the electronic energy spectrum of the CE phase depend on the ratio between the values of the Hund exchange and the splitting. When the splitting is sufficiently large, the Jahn-Teller effect stabilizes the insulating state. The finite value of the Hund coupling also favors the stabilization of the CE phase for the realistic values of the interionic exchange and the hopping integral of itinerant electrons.     

Dynamic critical phenomena in two-dimensional fully frustrated Coulomb gas model with disorder

The dynamic critical phenomena near depinning transition in two-dimensional fully frustrated square lattice Coulomb gas model with disorders was studied using Monte Carlo technique. The ground state of the model system with disorder σ=0.3 is a disordered state. The dependence of charge current density J on electric field E was investigated at low temperatures. The nonlinear J-E behavior near critical depinning field can be described by a scaling function proposed for three-dimensional flux line system [M.B. Luo, X. Hu, Phys. Rev. Lett. 98 (2007) 267002]. We evaluated critical exponents and found an Arrhenius creep motion for field region Ec/2<E<Ec. The scaling law of the depinning transition is also obtained from the scaling function.     

Conformation and dipole moment of tetrahydropyran-4-one by microwave spectroscopy

The microwave spectrum of tetrahydropyran-4-one has been studied in the frequency region 18 to 40 GHz. The rotational constants for the ground state and nine vibrationally excited states have been derived by fitting a-type R-branch transitions. The rotational constants for the ground state are (in MHz) A = 4566.882 ± 0.033, B = 2538.316 ± 0.003, C = 1805.878 ± 0.004. From information obtained from the gas-phase far-infrared spectrum and relative intensity measurements, these excited states are estimated to be ～ 100 cm^?1 above the ground state for the first excited state of the ring-bending and ～ 185 cm^?1 for the first excited state of the ring-twisting mode. Stark displacement measurements were made for several transitions and the dipole moment components determined by least-squares fitting of the displacements: (in Debye) |μ_a| = 1.693 (0.001), |μ_b| = 0.0, |μ_c| = 0.300 (0.013) yielding a total dipole moment μ_tot = 1.720 (0.003). A model calculation to reproduce the rotational parameters indicates that the data are consistent with the chair conformation.     

On the vacancy in a metal

The self-consistent calculations of spatial distributions of electrons and potentials in an isolated spherical cavity (with atomic radius R _WS) of the Wigner-Seitz cell, the energy of the vacancy formation, and the vacancy contribution to the electrical resistance have been performed in terms of the modified Kohn-Sham method and the stabilized jellium model. The energy shift of the ground state of electrons in the Wigner-Seitz cell with radius R _v ? R _WS (where R _v is the average distance between vacancies), the contribution of vacancies to the electron work function, and the effective mass of electrons have been found using the calculated phase shifts of the scattering wave functions and the representation of a system of vacancies as a “superlattice” in a metal.     

The ground state well depth position Rm of Van der Waals molecules and the spectral line shapes

As the ground state potential curve is strongly related to spectral line shapes, the minumum position of the ground state potential is obtained from the experiemental absorption profile k(Δν, T) at high density of the radiating atoms. The temperature dependence of the absorption processes of Hg and Cd lines 253.65 and 326.1 nm, respectively perturbed by inert gases (Xe, Kr, Ar and Ne) had been carefully studied over a wide spectral range. Using the point of the maximum temperature dependence Δν_m in each case, we are able to calculate the position of the ground state potential R_m using a simple formula.     

Kac-Moody symmetries of critical ground states

The symmetries of critical ground states of two-dimensional lattice models are investigated. We show how mapping a critical ground state to a model of a rough interface can be used to identify the chiral symmetry algebra of the conformal field theory that describes its scaling limit. This is demonstrated in the case of the six-vertex model, the three-coloring model on the honeycomb lattice, and the four-coloring model on the square lattice. These models are critical and they are described in the continuum by conformal field theories whose symmetry algebras are the su(2)_k=1, su(3)_k=1, and the su(4)_k=1 Kac-Moody algebra, respectively. Our approach is based on the Frenkel-Kac-Segal vertex operator construction of level-one Kac-Moody algebras.     

Model nuclear matter calculations in several Brueckner and Green's function theories

Model nuclear matter calculations are performed using two versions of the Brueckner theory (standard lowest order theory and a version with self-consistent “physical” onshell insertions in particle lines) and three Green's function theories (Λ ₀₀,Λ ₁₀ and Galitskii's ladder approximation). Ground state properties are derived using a strongs-wave nonlocal separable nucleon-nucleon potential. We investigate the differences between the results obtained using different theories, stemming from different treatment of the exclusion principle and of dispersive effects of the medium. The effect of the off-shell self-consistency in theΛ ₁₀ theory is found to be important.