209 research outputs found
Screened Exchange Corrections to the Random Phase Approximation from Many-Body Perturbation Theory
The random phase approximation (RPA) systematically overestimates the magnitude of the correlation energy and generally underestimates cohesive energies. This originates in part from the complete lack of exchange terms that would otherwise cancel Pauli exclusion principle violating (EPV) contributions. The uncanceled EPV contributions also manifest themselves in form of an unphysical negative pair density of spin parallel electrons close to electron-electron coalescence. We follow considerations of many-body perturbation theory to propose an exchange correction that corrects the largest set of EPV contributions, while having the lowest possible computational complexity. The proposed method exchanges adjacent particle/hole pairs in the RPA diagrams, considerably improving the pair density of spin-parallel electrons close to coalescence in the uniform electron gas (UEG). The accuracy of the correlation energy is comparable to other variants of second-order screened exchange (SOSEX) corrections although it is slightly more accurate for the spin-polarized UEG. Its computational complexity scales as O(N-5) or O(N-4) in orbital space or real space, respectively. Its memory requirement scales as O(N-2)
New measure of electron correlation
We propose to quantify the "correlation" inherent in a many-electron (or
many-fermion) wavefunction by comparing it to the unique uncorrelated state
that has the same single-particle density operator as it does.Comment: Final version to appear in PR
The calculation method of interaction between metal atoms under influence of the radiation
A method of calculation of interatomic interaction potentials in the presence of ionized states has been developed. They have been obtained for the atoms with different ionization degree on example of aluminum. The Heine-Abarenkov-Animalu model potential form factors was employed. The form factor parameters of ionized atoms was determined on the base of the quantum defect method using the atomic-spectroscopy data. The potential of interatomic interaction for different charged states with different degree of ionization were determined
Exchange and correlation as a functional of the local density of states
A functional is presented, in which the exchange
and correlation energy of an electron gas depends on the local density of
occupied states. A simple local parametrization scheme is proposed, entirely
from first principles, based on the decomposition of the exchange-correlation
hole in scattering states of different relative energies. In its practical
Kohn-Sham-like form, the single-electron orbitals become the independent
variables, and an explicit formula for the functional derivative is obtained.Comment: 5 pages. Expanded version. Will appear in Phys. Rev.
Pair distribution function in a two-dimensional electron gas
We calculate the pair distribution function, , in a two-dimensional
electron gas and derive a simple analytical expression for its value at the
origin as a function of . Our approach is based on solving the
Schr\"{o}dinger equation for the two-electron wave function in an appropriate
effective potential, leading to results that are in good agreement with Quantum
Monte Carlo data and with the most recent numerical calculations of . [C.
Bulutay and B. Tanatar, Phys. Rev. B {\bf 65}, 195116 (2002)] We also show that
the spin-up spin-down correlation function at the origin, , is mainly independent of the degree of spin polarization of
the electronic system.Comment: 5 figures, pair distribution dependence with distance is calculate
Operando and High-throughput multicscale-tomography
We report about multiscale tomography with high throughput at the Diamond beamline I13L. The beamline has the purpose of multi-scale and operando imaging and consists of two independent branchlines operating in real and reciprocal space. The imaging branch -called Diamond-Manchester branchline- hosts micro-tomography, grating interferometry and a full-field microscope. For rapid recording a broad spectrum of the undulator radiation is used either with band-passing the light with a combination of a filter and a deflecting mirror or using a multilayer monochromator. For all the methods similar recording times can be achieved, with typical scanning times of some minutes and covering the resolution range from microns to the 100nm range. Most recently a robot arm has been installed to increase the throughput to 300 samples per day. The system is now implemented for user operation in remote operation mode for the micro-tomography setup and can be expanded to the two other experiments. The instrumental capabilities are applied on various topics such as the study of biodiversity of insects or the structural variations of electrode materials in batteries. Fast recording with dedicated sample environments (not using the sample changing robot) enables operando studies in many areas, the charging/discharging cycles on batteries, the degradation of teeth enamel under various conditions or loading brine sandstone mixtures with CO2, to name some examples. For imaging with highest spatial resolution we managed to improve significantly the recording speed of ptycho-tomography, which is now in the order of hours and will be reduced further. We demonstrated in the past 2-D recording with 10kHz and expand the instrumental capability with specific hardware dependent triggering and scanning schemes. We expand the research program for multi-scale imaging across both branchlines (imaging and coherence branchlines) with first studies such as batteries, brain research, concrete
Accurate evaluation of the interstitial KKR-Green function
It is shown that the Brillouin zone integral for the interstitial KKR-Green
function can be evaluated accurately by taking proper care of the free-electron
singularities in the integrand. The proposed method combines two recently
developed methods, a supermatrix method and a subtraction method. This
combination appears to provide a major improvement compared with an earlier
proposal based on the subtraction method only. By this the barrier preventing
the study of important interstitial-like defects, such as an electromigrating
atom halfway along its jump path, can be considered as being razed.Comment: 23 pages, RevTe
Femtosecond multimodal imaging with a laser-driven X-ray source
Laser-plasma accelerators are compact linear accelerators based on the interaction of high-power lasers with plasma to form accelerating structures up to 1000 times smaller than standard radiofrequency cavities, and they come with an embedded X-ray source, namely betatron source, with unique properties: small source size and femtosecond pulse duration. A still unexplored possibility to exploit the betatron source comes from combining it with imaging methods able to encode multiple information like transmission and phase into a single-shot acquisition approach. In this work, we combine edge illumination-beam tracking (EI-BT) with a betatron X-ray source and present the demonstration of multimodal imaging (transmission, refraction, and scattering) with a compact light source down to the femtosecond timescale. The advantage of EI-BT is that it allows multimodal X-ray imaging technique, granting access to transmission, refraction and scattering signals from standard low-coherence laboratory X-ray sources in a single shot
A Geometric Formulation of Quantum Stress Fields
We present a derivation of the stress field for an interacting quantum system
within the framework of local density functional theory. The formulation is
geometric in nature and exploits the relationship between the strain tensor
field and Riemannian metric tensor field. Within this formulation, we
demonstrate that the stress field is unique up to a single ambiguous parameter.
The ambiguity is due to the non-unique dependence of the kinetic energy on the
metric tensor. To illustrate this formalism, we compute the pressure field for
two phases of solid molecular hydrogen. Furthermore, we demonstrate that
qualitative results obtained by interpreting the hydrogen pressure field are
not influenced by the presence of the kinetic ambiguity.Comment: 22 pages, 2 figures. Submitted to Physical Review B. This paper
supersedes cond-mat/000627
Editors’ choice—4D neutron and X-ray tomography studies of high energy density primary batteries: Part II. multi-modal microscopy of LiSOCl2 cells
The ability to track electrode degradation, both spatially and temporally, is fundamental to understand performance loss during operation of lithium batteries. X-ray computed tomography can be used to follow structural and morphological changes in electrodes; however, the direct detection of electrochemical processes related to metallic lithium is difficult due to the low sensitivity to the element. In this work, 4-dimensional neutron computed tomography, which shows high contrast for lithium, is used to directly quantify the lithium diffusion process in spirally wound Li/SOCl primary cells. The neutron dataset enables the quantification of the lithium transport from the anode and the accumulation inside the SOCl cathode to be locally resolved. Complementarity between the collected neutron and X-ray computed tomographies is shown and by applying both methods in concert we have observed lithium diffusion blocking by the LiCl protection layer and identified all cell components which are difficult to distinguish using one of the methods alone
- …