180 research outputs found
Polaronic distortion and vacancy-induced magnetism in MgO
The electronic structure of the neutral and singly charged Mg vacancy in MgO
is investigated using density functional theory. For both defects, semilocal
exchange correlation functionals such as the local spin density approximation
incorrectly predict a delocalized degenerate ground state. In contrast
functionals that take strong correlation effects into account predict a
localized solution, in agreement with spin resonance experiments. Our results,
obtained with the HSE hybrid, atomic self-interaction corrected and LDA+U
functionals, provide a number of constraints to the possibility of
ferromagnetism in hole doped MgO
Electric field control of valence tautomeric interconversion in Cobalt dioxolene
We demonstrate that the critical temperature for valence tautomeric
interconversion in Cobalt dioxolene complexes can be significantly changed when
a static electric field is applied to the molecule. This is achieved by
effectively manipulating the redox potential of the metallic acceptor forming
the molecule. Importantly our accurate density functional theory calculations
demonstrate that already a field of 0.1 V/nm, achievable in Stark spectroscopy
experiments, can produce a change in the critical temperature for the
interconversion of 20 K. Our results indicate a new way for switching on and
off the magnetism in a magnetic molecule. This offers the unique chance of
controlling magnetism at the atomic scale by electrical means
Transmission through correlated CunCoCun heterostructures
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al.We propose a method to compute the transmission through correlated heterostructures by combining density functional and many-body dynamical mean field theories. The heart of this combination consists in porting the many-body self-energy from an all electron basis into a pseudopotential localized atomic basis set. Using this combination we study the effects of local electronic interactions and finite temperatures on the transmission across the Cu4CoCu4 metallic heterostructure. It is shown that as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority-spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant d-electron contribution, as compared to the noncorrelated case in which the transport is dominated by s and p electrons.Financial support offered by the Augsburg Center for Innovative Technologies and by the Deutsche Forschungsgemeinschaft (through TRR 80) is gratefully acknowledged.
A.D. and I.R. acknowledge financial support from the European Union through the EU FP7 program through project 618082 ACMOL. M.R. also acknowledges support by the Ministry of Education, Science, and Technological Development of the Republic of Serbia under Projects No. ON171017 and No. III45018. A.O. would like to acknowledge financial support from the Axel Hultgren foundation and the Swedish steel producer’s association (Jernkontoret). L.V. acknowledges support from the Swedish Research Council.Peer Reviewe
Spin-orbit induced equilibrium spin currents in materials
The existence of pure spin currents in absence of any driving external field is commonly considered an exotic phenomenon appearing only in quantum materials, such as topological insulators. We demonstrate instead that equilibrium spin currents are a rather general property of materials with non-negligible spin-orbit coupling (SOC). Equilibrium spin currents can be present at the surfaces of a slab. Yet, we also propose the existence of global equilibrium spin currents, which are net bulk spin currents along specific crystallographic directions of solid-state materials. Equilibrium spin currents are allowed by symmetry in a very broad class of systems having gyrotropic point groups. The physics behind equilibrium spin currents is uncovered by making an analogy between electronic systems with SOC and non-Abelian gauge theories. The electron spin can be seen as analogous to the color degree of freedom in SU(2) gauge theories and equilibrium spin currents can then be identified with diamagnetic color currents appearing as the response to a effective non-Abelian magnetic field generated by the SOC. Equilibrium spin currents are not associated with spin transport and accumulation, but they should nonetheless be carefully taken into account when computing transport spin currents. We provide quantitative estimates of equilibrium spin currents for a number of different systems, specifically the Au(111) and Ag(111) metallic surfaces presenting Rashba-type surface states, nitride semiconducting nanostructures, and bulk materials, such as the prototypical gyrotropic medium tellurium. In doing so, we also point out the limitations of model approaches showing that first-principles calculations are needed to obtain reliable predictions. We therefore use density functional theory computing the so-called bond currents, which represent a powerful tool to deeply understand the relation between equilibrium currents, electronic structure, and crystal point group
Transmission through correlated CuCoCu heterostructures
The effects of local electronic interactions and finite temperatures upon the
transmission across the CuCoCu metallic heterostructure are studied in
a combined density functional and dynamical mean field theory. It is shown
that, as the electronic correlations are taken into account via a local but
dynamic self-energy, the total transmission at the Fermi level gets reduced
(predominantly in the minority spin channel), whereby the spin polarization of
the transmission increases. The latter is due to a more significant
-electrons contribution, as compared to the non-correlated case in which the
transport is dominated by and electrons.Comment: 29 pages, 7 figures, submited to PR
The ground state of a spin-crossover molecule calculated by diffusion Monte Carlo
Spin crossover molecules have recently emerged as a family of compounds
potentially useful for implementing molecular spintronics devices. The
calculations of the electronic properties of such molecules is a formidable
theoretical challenge as one has to describe the spin ground state of a
transition metal as the legand field changes. The problem is dominated by the
interplay between strong electron correlation at the transition metal site and
charge delocalization over the ligands, and thus it fits into a class of
problems where density functional theory may be inadequate. Furthermore, the
crossover activity is extremely sensitive to environmental conditions, which
are difficult to fully characterize. Here we discuss the phase transition of a
prototypical spin crossover molecule as obtained with diffusion Monte Carlo
simulations. We demonstrate that the ground state changes depending on whether
the molecule is in the gas or in the solid phase. As our calculation provides a
solid benchmark for the theory we then assess the performances of density
functional theory. We find that the low spin state is always over-stabilized,
not only by the (semi-)local functionals, but even by the most commonly used
hybrids (such as B3LYP and PBE0). We then propose that reliable results can be
obtained by using hybrid functionals containing about 50% of exact-exchange
Electronic and magnetic properties of the interface between metal-quinoline molecules and cobalt
Enhanced recovery after surgery and video-assisted thoracic surgery lobectomy: The Italian VATS Group* surgical protocol
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