Magnetpolaron effect in two-dimensional anisotropic parabolic quantum dot in a perpendicular magnetic field

We study the two-dimensional weak-coupling Fr o¨hlich polaron in a completely anisotropic quantum dot in a perpendicular magnetic field. By performing a unitary transformation, we first transform the Hamiltonian into a new one which describes an anisotropic harmonic oscillator with new mass and trapping frequencies interacting with the same phonon bath but with different interaction form and strength. Then employing the second-order Rayleigh–Schr o¨dinger perturbation theory, we obtain the polaron correction to the ground-state energy. The magnetic field and anisotropic effects on the polaron correction to the ground-state energy are discussed.     

B$lt;sub$gt;$lt;i$gt;n$lt;/i$gt;$lt;/sub$gt;($lt;i$gt;n$lt;/i$gt;=2—15)团簇的几何结构和电子性质

应用密度泛函理论中的B3LYP方法计算并分析了不同生长模式下B_n（n=2—15）团簇的几何结构及电子性质. 同时,比较和讨论了不同生长模式下硼团簇的原子束缚能、能级间隙和第一电离势. 研究表明：直线构型稳定性最低,金属性较强,尤其在n=8时能隙仅有0.061 eV,说明该团簇已具有金属特征. 平面或准平面构型稳定性最高,非金属性强. 立体构型的稳定性与金属性介于直线和平面构型之间. 另外,还讨论了基态团簇的束缚能、能量二阶差分、能级间隙和第一电离势随团簇尺寸的变化,结果表明B₁₂与B₁₄是幻数团簇. 关键词： n团簇')" href="#">B_n团簇 密度泛函理论 几何结构 电子性质     

Odd-particle systems in the shell model monte carlo method: circumventing a sign problem

The shell model Monte Carlo method is a powerful technique to calculate thermal and ground-state properties of strongly correlated finite-size systems. However, its application to odd-particle-number systems has been hampered by the sign problem that originates from the projection on an odd number of particles. We circumvent this sign problem for the ground-state energy by extracting the ground-state energy of the odd-particle-number system from the asymptotic behavior of the imaginary-time single-particle Green's function of the even-particle-number system. We apply this method to calculate pairing gaps of nuclei in the iron region. Our results are in good agreement with experimental pairing gaps.     

The ground-state lifetime of polaron in a parabolic quantum dot

This paper reports that the ground-state energy of polaron was obtained with strong electron-LO-phonon coupling by using a variational method of the Pekar type in a parabolic quantum dot. Quantum transition is occurred in the quantum system due to the electron-phonon interaction and the influence of temperature. That is the polaron transit from the ground-state to the first-excited state after absorbing a LO-phonon and it causes the change of the polaron lifetime. Numerical calculations are performed and the results illustrate that the ground-state lifetime of the polaron will increase with increasing the ground-state energy of polaron and decrease with increasing the electron-LO-phonon coupling strength, the confinement length of the quantum dot and the temperature.     

Exact expression of the ground-state energy for the symmetric anderson model

The exact expression of the ground-state energy for the symmetric Anderson model is obtained with the use of the Wiegmann approach. It is found that some of the quasi-momenta appearing in Wiegmann's paper are necessarily complex to obtain the expression of the ground-state energy.     

Ground-State Properties of Charged Bosons Confined in a One-Dimensional Harmonic Double-Well Trap： Diffusion Monte Carlo Calculations

The diffusion Monte Carlo method is applied to study the ground-state properties of charged bosons in one dimension confined in a harmonic double-well trap. The particles interact repulsively through a Coulombic 1/r potential. Numerical results show that the well separation has significant influence on the ground-state properties of the system. When the interaction of the system is weak, ground-state energy decreases with the increasing well separation and has a minimal value. If the well separation increases continually~ the ground-state energy increases and approaches to a constant gradually. This effect will be abatable in the strong interacting system. In addition, by calculating the density of the systems for different interaction strengths with various well separations, we find that the density increases abnormally when the well separation is large at the centre of the system.     

Origin of the ground-state energy of a particle in a potential well

In this paper, an apparently universal feature of the ground-state energy of a particle in a potential well is pointed out. Namely, by the example of an infinitely deep rectangular potential well, we clearly demonstrate that this energy, as well as the localization energy of a particle ensuing from the Heisenberg relation, is accumulated by the work of an external force against the particle pressure force on the well walls during compression of the particle substance and, correspondingly, its wave function ψ from unbounded free space to the finite volume of the well. This work is exactly equal to the particle ground-state energy.     

Probing the structural,electronic and magnetic properties of small Au4M (M = Sc–Zn) clusters

Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au₄M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au₄M clusters favour the most highly coordinated position. The ground-state Au₄M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au₄M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au₄Ti, Au₄Mn and Au₄Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au₄M cluster is mainly localised on the M atom and vary from 0 to 5 μ_B by substituting an Au atom in Au₅ cluster with different transition-metal atoms.     

Energy analysis of a toroidal magnetohydrodynamic plasma with fluid motion

Summary The relaxation process in an ideal magnetohydrodynamic (MHD) plasma with fluid velocity and enclosed in a toroidal vessel has been discussed. The expressions for the field parameters and the energy state of the system have been derived. The expression for the minimum energy state of the system has been deduced. An analysis of the conservation of energy of the system in the presence of weak and strong magnetic fields has also been presented. The author of this paper has agreed to not receive the proofs for correction. This work was commenced and partly completed during author's short stay at I.C.T.P.-Trieste, Italy, in 1988.     

普适性双原子分子解析势能函数的研究

提出了一种构造解析势能函数的新方法,由此得到了一种既适用于中性双原子分子又适用于带电双原子分子离子的解析势能函数。本文用八种基本类型的双原子分子——同核中性基态双原子分子Na₂-X1Σ+_g,同核中性激发态双原子分子C₂-A1Π_u,同核带电基态双原子分子离子He+₂-X2Σ+_u,同核带电激发态双原子分子离子N+₂-B2Σ+_u,异核中性基态双原子分子NaLi-X1Σ+_g,异核中性激发态双原子分子BH-B1Σ+,异核带电基态双原子分子离子(BC)--X3Π,异核带电激发态双原子分子离子(CS)+-A2Π等共21个算例对势能函数进行了验证并与RKR (Rydberg-Klein-Rees)实验数据进行了比较,计算结果与RKR数据符合很好。     

Improved (1s)<Superscript>2</Superscript> variational model for helium

The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e ^−γ(rA/a _o)ⁿe^−γ(rB/a _o)ⁿ. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n” as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit on the ground state energy of −2.86107 E _h (E _h =1 hartree) in comparison with the traditional (n=1) result of −2.84766 E _h . This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E _h ) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168 E _h , the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ) are determined to be ≈(0.897, 1.825).     

Electron correlations in a C20 fullerene cluster

The ground-state properties of C₂₀ fullerene clusters are determined in the framework of the Hubbard model by using lattice density-functional theory (LDFT) and scaling approximations to the interaction-energy functional. Results are given for the ground-state energy, kinetic and Coulomb energies, local magnetic moments, and charge-excitation gap, as a function of the Coulomb repulsion U/t and for electron or hole doping δ close to half-band filling (|δ| ≤1). The role of electron correlations is analyzed by comparing the LDFT results with fully unrestricted Hartree-Fock (UHF) calculations which take into account possible noncollinear arrangements of the local spin-polarizations. The consequences of the spin-density-wave symmetry breaking, often found in UHF, and the implications of this study for more complex fullerene structures are discussed.     

Estimating ground-state energies in supersymmetric quantum mechanics: (2) Unbroken case

In this second paper studying supersymmetric quantum mechanics, we concentrate on cases where supersymmetry is not spontaneously broken. This is done to further study the importance of various contributions to the ground-state energy. We perform an instanton calculation in detail and show that estimates of the ground-state energy based on the instanton contribution are poor-usually a naive zero-point energy calculation gives as good an estimate. We test the method developed in the previous paper and show that it gives good results for these cases, as before. We question the common assumptions that instanton effects are exponentially small compared to the perturbative scale, and that instanton contributions are necessarily suppressed by powers ofh.     

Influence of Electric and Magnetic Fields on the Polaron in a Quantum Well

A combinative method of variational wavefunction and harmonic oscillator operator algebra, the ground-state energy correction to an electron confined in the quantum well of GaAs/Ga_1-xAl_x, As in the electric and magnetic fields along the growth axis has been studied by taking into account the interaction of different optical phonon modes with the electron. The ground-state energy is obtained as a function of the well width and the strength of electric and magnetic fields. The results show that the magnetic field greatly enhances the in terface-phonon part of the polaronic correction to electron ground-state energy in the well width d ≤ 300 Å. The electric field also enhances the polaron effect of interface mode, but decreases the part of bulk longitudinal mode.     

Hydrogenic impurity states in wurtzite GaN/AlGaN coupled quantum dots

The ground-state binding energy of a hydrogenic donor impurity in wurtzite (WZ) GaN/AlGaN coupled quantum dots (QDs) is calculated by means of a variational method, considering the strong built-in electric fields caused by the piezoelectricity and spontaneous polarizations. The strong built-in electric fields induce an asymmetrical distribution of the ground-state binding energy with respect to the center of the coupled QDs. If the impurity is located at the low dot, the ground-state binding energy is insensitive to the interdot barrier width of WZ GaN/AlGaN coupled QDs.     

Quantum coherence and ground-state phase transition in a four-chain Bose–Hubbard model

We study the quantum coherence and ground-state phase transition of a four-chain Bose–Hubbard model with the long-range interaction. In a special four-chain Bose–Hubbard model,i.e., each chain only has one optical potential, four types of the ground-state phases are discovered. The effects of the disorder, the on-site interaction and the long-range interaction on the quantum coherence are studied. For the system without the long-range interaction, the quantum coherence changes from one periodic oscillation to two periodic oscillations as the onsite interaction increases. By considering the long-range interaction, the quantum coherence goes back to one periodic oscillation again. The on-site interaction itself suppresses the quantum coherence, both the on-site interaction and long-range interaction together enhance the quantum coherence with the weak disorder. If the disorder strength is increased beyond a critical value,they start to suppress the quantum coherence. In a regular four-chain Bose–Hubbard model, i.e.,each chain has many optical potentials, the ground-state phase transitions are obtained by using the cluster Gutzwiller mean-field method. Exotic ground-state phases are found, i.e., superfluid phase, integer Mott insulator phase, supersolid phase and loophole insulator phase. The combination of the loophole insulator phase and the supersolid phase expands the lobes with the half-integer filling per site for the small ratio β = t_■/t_⊥.     

Solid hydrogen. Ground-state energy,pressure, compressibility and phase transition at high densities

The ground-state energy, the pressure and the compressibility of solid molecular hydrogen is calculated by means of a modified Brueckner theory. The Bethe-Gold-stone equation is solved to give the reaction matrix or the effective interaction in coordinate space, and the ground-state energy for hcp and fcp hydrogen is calculated. Also, the pressure and the compressibility is estimated from the dependence of the ground-state energy on density or molar volume. The possibility of a phase transition from solid molecular hydrogen into a metallic atomic phase is also considered. The ground-state energy and pressure for bcc atomic hydrogen is calculated, and a phase transition is found to occur at a pressure of 1.2·10⁶ atm.     

The structure of ion-acoustic waves in a low-frequency three-component electron–ion space plasma with two-electron populations

In the present paper, we have studied the binding energy of the shallow donor hydrogenic impurity, which is confined in an inhomogeneous cylindrical quantum dot (CQD) of \(\hbox {GaAs-Al}_{x}\hbox {Ga}_{1-x}\hbox {As}\). Perturbation method is used to calculate the binding energy within the framework of effective mass approximation and taking into account the effect of dielectric mismatch between the dot and the barrier material. The ground-state binding energy of the donor is computed as a function of dot size for finite confinement. The result shows that the ground-state binding energy decreases with the increase in dot size. The result is compared with infinite dielectric mismatch as a limiting case. The binding energy of the hydrogenic impurity is maximum for an on-axis donor impurity.     

Triaxiality in Neutron-Rich As Isotopes with Covariant Density Functional Theory

The relativistic mean-field model with density-dependent DD-ME2 and DD-PC1 interactions has been used for the investigation of the ground-state shape evolution of neutron-rich ^83–91 As isotopes. For this purpose, the potential energy curve and the potential energy surface of each nucleus of interest have been examined. From analyzing the potential energy surfaces of the neutron-rich ^83–91 As isotopic chain, ⁸⁷ As is suggested to be a possible candidate for triaxial nucleus. Furthermore, studies of some ground-state nuclear properties of As isotopes such as energy, size and deformation have been obtained.