Modern Physics Letters B

The wavefunction method provides us with a useful tool to describe electron correlations in solids at the ground state. In this paper we review the recent development of the momentum-dependent local ansatz (MLA) wavefunction. It is constructed by taking into account two-particle excited states projected onto the local orbitals, and the momentum-dependent amplitudes of these states are chosen as variational parameters. The MLA describes accurately correlated electron states from the weak to the intermediate Coulomb interaction regime in infinite dimensions, and works well even in the strongly correlated region by introducing a new starting wavefunction called the hybrid (HB) wavefunction. The MLA-HB is therefore shown to overcome the limitation of the original local ansatz (LA) wavefunction as well as the Gutzwiller wavefunction. In particular, the calculated quasiparticle weight versus Coulomb interaction curve is shown to be close to that obtained by the numerical renormalization group approach. It is also shown that the MLA is applicable to the first-principles Hamiltonian.

In the present work, the energy levels and transition frequency between relevant levels of the strong-coupling polaron in a Gaussian quantum dot is studied. In this regard, we have used the well known Lee–Low–Pines unitary transformation method and the Pekar type variational procedure. We show the effect of the effective confinement length and electron–phonon (e–p) coupling strength on energy levels and the transition frequency. According to the results, it is found that the energy levels are decreased with increasing the e–p coupling strength. Also, the transition frequency is increased with enhancing the e–p coupling strength. The energy levels and transition frequency are increased with decreasing the effective confinement lengths.

In this paper, we investigate the adsorption of a series of rare-earth (RE) metal atoms (La, Pr, Nd, Sm and Eu) on the pristine zigzag (8, 0) silicon carbide nanotube (SiCNT) using density functional theory (DFT). Main focuses are placed on the stable adsorption sites, the corresponding binding energies, and the modified electronic properties of the SiC nanotubes due to the adsorbates. A single RE atom prefers to adsorb strongly at the hollow site with relatively high binding energy (larger than 1.0 eV). Due to the rolling effect of single-walled SiCNTs, the inside configurations are more stable than the outside ones. For RE-adsorbed systems, the adsorption of metal atoms induces certain impurity states within the band gap of the pristine SiCNT. Furthermore, we analyze there exists hybridizations between RE-5d, 6s, C-2p and Si-3p orbitals for the RE atom adsorption on the SiCNTs.

The structural and electric properties of Ni_0.65-xZn_0.35Cd_xFe₂O₄ (0 ≤ x ≤ 0.2) prepared by standard ceramic technique, have been studied. For all x values, X-ray powder diffraction was performed and the lattice constants and oxygen parameters were drawn from experimental data. Based on these values, other structural parameters like cation–cation, cation–anion distances, bond angles and hopping length were calculated, and the cation distribution was proposed by comparing observed and calculated X-ray diffraction intensities. It was found that substitution of larger cadmium into the lattice resulted in a significant change in the structural parameters. The microstructure of the samples was investigated using SEM micrographs and we found a substantial grain growth (observed mainly for x = 0.16 and 0.20) due to cadmium diffusion. Carrier mobilities for all samples were drawn from our DC electrical conductivity results and the variation of mobility with composition and temperature is presented. Dielectric measurements were performed at a standard frequency 1 kHz and the dielectric constant and loss factor were found to decrease first from x = 0 to x = 0.12 with the abrupt increase above this composition.

In our previous experiments, it has been found that an angle of asymmetry is present when the breakdown of the Lorenz invariance occurs. We want to make sure that this angle is present as a preferred direction of emission for α-rays and neutrons emitted as a result of piezonuclear reactions, or better, the reactions in deformed spacetime (DST-reactions: deformed spacetime reactions, for more details on the DST-reactions [see G. Albertini et al., Material and Process for Energy, ed. A. Mendez-Vilas (Formatex, 2013)]. For this purpose, we analyze the experiment of Ancona for α-ray emission and the experiment of Cagliari for neutrons emission. In this work, we present an example for each group of experiments. These experimental examples are significant because they show the behavior of the emissions detected in all the measures.

Size-dependent melting temperature of metallic nanoparticles is studied theoretically based on cohesive energy. Three factors are introduced in the present model. The k factor, i.e. efficiency of space filling of crystal lattice is defined as the ratio between the volume of the atoms in a crystal cell and that of the crystal cell. The β factor is defined as the ratio between the cohesive energy of surface atom and interior atom of a crystal. The q_s factor represents the packing fraction on a surface crystalline plane. Considering the β, q_s and k factors, the relationship between melting temperature and nanoparticle size is discussed. The obtained model is compared with the reported experimental data and the other models.

Using first-principles calculation based on density functional theory, the elastic stability and dynamic stability of heavier alkali metals K, Rb and Cs in sc structure are investigated. Results reveal that the C₄₄ instabilities are responsible for the mechanical instabilities for these heavier alkali metals and the spin-polarization phases are more stable than non-spin-polarization phases. Other than K-sc which presents BZ edge instability at the M-point at ambient condition, the K-sc and Rb-sc are dynamically stable for the range of the pressure in our calculation. But for Cs-sc, it becomes unstable starting from 7 GPa. Especially we demonstrate that the most stable phases of K at low temperatures and pressures around 20 GPa are ferromagnetic K in sc structure.

In this paper, Dresselhaus spin-orbit coupling (SOC) modulating quantum pumps driven by triple time-dependent potentials are investigated, where the pump center are semiconductors connected to two normal leads. In detail, the parametric influence to the quantum pump current is studied by using the Floquet scattering technology, and mainly via the modulations of the potentials position, the SOC strength and component, the tunable currents pumped from the system are discussed.