Search results for "density [muon]"
showing 10 items of 313 documents
Electronic properties of single-walled carbon nanotubes inside cyclic supermolecules
2006
Possible ways for manipulating carbon nanotubes (CNTs) with cyclic supermolecules are studied using density functional theory. Electronic structure calculations with structure optimizations have been performed for the (4,4) and (8,0) single-walled carbon nanotubes (SWNTs) complexed with crown ethers as well as for the (4,0) SWNT with beta-cyclodextrin. A slight polarization of charge in both the nanotube and the supermolecule is observed upon rotaxane complexation, but the interaction is mainly repulsive, and the systems stay 2.8-3.5 A apart. The supermolecule does not affect the electronic band structure of the nanotube significantly within such a configuration. The situation differs notic…
E0 suppression in pion photoproduction on 13C
1990
Abstract Recently measured anomalously low cross sections for 13 C(γ, π − ) 13 N at low energy and θ π lab = 90° 0761 have been analyzed in a DWIA calculation. It has been found that the EO contribution alone is able to explain the data, so that the M1 cross section is expected to vanish. Using constraints from recent magnetic electron scattering, an explanation is possible by assuming a significantly lower reduced density matrix element for spin-flip isovector transitions with angular momentum L = 2 than predicted by Cohen and Kurath.
State-of-the-art density matrix renormalization group and coupled cluster theory studies of the nitrogen binding curve.
2004
We study the nitrogen binding curve with the density matrix renormalization group (DMRG) and single-reference and multireference coupled cluster (CC) theory. Our DMRG calculations use up to 4000 states and our single-reference CC calculations include up to full connected hextuple excitations. Using the DMRG, we compute an all-electron benchmark nitrogen binding curve, at the polarized, valence double-zeta level (28 basis functions), with an estimated accuracy of 0.03mE_h. We also assess the performance of more approximate DMRG and CC theories across the nitrogen curve. We provide an analysis of the relative strengths and merits of the DMRG and CC theory under different correlation condition…
Element-Specific Magnetic and Electronic Properties of Epitaxial Heusler Films
2015
X-ray magnetic circular dichroism (XMCD) provides an experimental access to element-specific electronic properties of thin epitaxial films of Heusler alloys. The combination of bulk-sensitive transmission and surface-sensitive electron yield methods reveals quantitative information on bulk and interface properties. Extreme cases of magnetically dead and life layers at interfaces illustrate the high potential of XMCD. The dependence of XMCD on disorder, structure and composition is discussed as well as dynamic properties investigated by a combination of ferromagnetic resonance and XMCD. Examples are shown where spectroscopic information provided by XMCD is exploited to discuss subtle changes…
Phase Behavior of TmVO4 under Hydrostatic Compression: An Experimental and Theoretical Study
2020
We present a structural and optical characterization of magnetoelastic zircon-type TmVO4 at ambient pressure and under high pressure. The properties under high pressure have been determined experimentally under hydrostatic conditions and theoretically using density functional theory. By powder X-ray diffraction we show that TmVO4 undergoes a first-order irreversible phase transition to a scheelite structure above 6 GPa. We have also determined (from powder and single-crystal X-ray diffraction) the bulk moduli of both phases and found that their compressibilities are anisotropic. The band gap of TmVO4 is found to be Eg = 3.7(2) eV. Under compression the band gap opens linearly, until it unde…
Efficient parallel tempering for first-order phase transitions
2007
We present a Monte Carlo algorithm that facilitates efficient parallel tempering simulations of the density of states g(E) . We show that the algorithm eliminates the supercritical slowing down in the case of the Q=20 and Q=256 Potts models in two dimensions, typical examples for systems with extreme first-order phase transitions. As recently predicted, and shown here, the microcanonical heat capacity along the calorimetric curve has negative values for finite systems.
Existence of zero-energy impurity states in different classes of topological insulators and superconductors and their relation to topological phase t…
2015
We consider the effects of impurities on topological insulators and superconductors. We start by identifying the general conditions under which the eigenenergies of an arbitrary Hamiltonian H belonging to one of the Altland-Zirnbauer symmetry classes undergo a robust zero energy crossing as a function of an external parameter which can be, for example, the impurity strength. We define a generalized root of \det H, and use it to predict or rule out robust zero-energy crossings in all symmetry classes. We complement this result with an analysis based on almost degenerate perturbation theory, which allows a derivation of the asymptotic low-energy behavior of the ensemble averaged density of st…
Crystallographic, electronic structure and magnetic properties of the GdTAl; T=Co, Ni and Cu ternary compounds
2000
Abstract Single phase GdCoAl, GdCuAl and single crystal GdNiAl samples of good quality were synthesized. The electrical resistivity, magnetization and AC susceptibility as a function of temperature revealed in all these compounds a ferromagnetic ordering at 100, 83 and 60 K, respectively. A magnetic transition, probably to a non-colinear structure was observed in GdNiAl at 31 K as well as the presence of the third magnetic transition at 14 K, while in the GdCuAl compound an evidence of similar transition was found at 23 K. In GdNiAl a transition between two different crystallographic phases of ZrNiAl-type was observed at 220 K. The transition was accompanied by rapid jumps of crystal lattic…
Transitions of tethered chain molecules under tension
2014
An applied tension force changes the equilibrium conformations of a polymer chain tethered to a planar substrate and thus affects the adsorption transition as well as the coil-globule and crystallization transitions. Conversely, solvent quality and surface attraction are reflected in equilibrium force-extension curves that can be measured in experiments. To investigate these effects theoretically, we study tethered chains under tension with Wang-Landau simulations of a bond-fluctuation lattice model. Applying our model to pulling experiments on biological molecules we obtain a good description of experimental data in the intermediate force range, where universal features dominate and finite…
First-Principles Study on Polymorphs of AgVO3: Assessing to Structural Stabilities and Pressure-Induced Transitions
2017
In this paper, we present a comprehensive theoretical study, based on density-functional theory calculations, and which focuses on the structural and electronic properties of silver vanadium oxide (AgVO3) in the monoclinic [Cm (β-AgVO3), C2/c (α-AgVO3), and Cc], orthorhombic (Amm2), and cubic (Pm3̅m) phases from 0–30 GPa. The structural and electronic properties, the stability of different phases, and the pressure-induced solid–solid phase transitions of AgVO3 have been previously studied. The effects of pressure on the band structures, energy–gap values, density of states, and vibrational frequencies are also studied. Numerical and analytical calculations are conducted to obtain the lattic…