1,720,978 research outputs found
Comment on "Nonadiabatic couplings from the Kohn-Sham derivative matrix: Formulation by time-dependent density-functional theory and evaluation in the pseudopotential framework"
Full text linkThe issue of the ab initio evaluation of the first-order nonadiabatic couplings (NAC's) is re-examined. In particular, a recent derivation in Phys. Rev. A 82, 062508 (2010) of the NAC's is corrected by performing an extension of the derivation to the case of arbitrary values of the Kohn-Sham (KS) occupation factors. A single expression for the nonadiabatic couplings, valid both for integer and fractional values of the KS occupation factors, is provided.Fil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin
Electric and magnetic field manipulation and storage of charge-tunable excitons
Full text linkThe excitonic spectrum of radially polarized semiconductor rings has been analyzed theoretically, in the presence of an in-plane electric field and a perpendicular magnetic field. Based on the numerically exact solution, a regime has been found where the exciton behaves as a single carrier or quasiparticle, with an effective and tunable electric charge determined by the ring geometry. A protocol is proposed for the storage of excitons without destroying them, consisting in converting them from “bright” to “dark,” by performing a sequence of well-defined steps. Accurate analytical approximations are provided for each of the exciton regimens found: quasifree, locked, and broken.Fil: Simonin, Jorge Marcos. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Pacheco, Mónica. Universidad de Santa María; ChileFil: Barticevic, Z.. Universidad de Santa María; Chil
Asymptotics of the metal-surface Kohn-Sham exact exchange potential revisited
No full textThe asymptotics of the Kohn-Sham (KS) exact exchange potential of a jelliumlike semi-infinite metal is investigated in the framework of the optimized-effective-potential formalism of density-functional theory. Our numerical calculations clearly show that deep into the vacuum side of the surface with being a system-dependent constant, thus, confirming the analytical calculations reported in Phys. Rev. B81, 121106(R) (2010)PRBMDO1098-012110.1103/PhysRevB.81.121106. A criticism of this work published in Phys. Rev. B85, 115124 (2012)PRBMDO1098-012110.1103/PhysRevB.85.115124 is shown to be incorrect. Our rigorous exchange-only results provide strong constraints both for the building of approximate exchange functionals and for the determination of the still unknown KS correlation potential.Fil: Horowitz, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Pitarke, J.M.. Universidad del País Vasco; España. Instituto Vasco de Investigación y Desarrollo; Españ
Performance of the spin-dependent Krieger-Li-Iafrate approximation in jellium slabs
Full text linkThe possible spin-polarized states of metallic jellium slabs have been studied by means of a Krieger-LiIafrate (KLI) approximation for the exchange potential. The stability of the different magnetic states has been determined by using a fixed-spin-moment method. Notably, in the search for solutions with different magnetizations, the KLI approximation leads to the sudden filling of electronic states for either majority or minority spin channels, and also to hysteresis effects, as the system crosses these points of discontinuity. These effects are completely missed by the local spin-density approximation (LSDA), which exhibits instead a continuous behavior. Close to the density corresponding to the Bloch instability of the homogeneous 3D electron gas, different exotic magnetic configurations appear, some of them featuring a spontaneous breaking of inversion symmetry around the slab center. As compared to the LSDA, the spin-dependent KLI approximation offers a moderate increase of the stability of a slab antiferromagnetic state.Fil: Horowitz, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Rigamonti, Santiago. Humboldt-Universität zu Berlin; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Becke-Johnson-type exchange potential for two-dimensional systems
Full text linkWe extend the Becke-Johnson approximation of the exchange potential to two dimensions. We prove and demonstrate that a direct extension of the underlying formalism may lead to divergent behavior of the potential. We derive a cure to the approach by enforcing the gauge invariance and correct asymptotic behavior of the exchange potential. The procedure leads to an approximation which is shown, in various quasi-two-dimensional test systems, to be very accurate in comparison with the exact-exchange potential and thus a considerable improvement over the commonly applied local-density approximation.Fil: Pittalis, S.. Freie Universität Berlin; Alemania. University of Missouri; Estados Unidos. European Theoretical Spectroscopy Facility; Estados UnidosFil: Räsänen, E.. Universidad de Jyvaskyla; FinlandiaFil: Proetto, Cesar Ramon. Freie Universität Berlin; Alemania. European Theoretical Spectroscopy Facility; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentin
Localized versus extended systems in density functional theory: Some lessons from the Kohn-Sham exact exchange potential
Full text linkA long-standing puzzle in density functional theory is the issue of the long-range behavior of the Kohn-Sham exchange-correlation potential at metal surfaces. As an important step toward its solution, it is proven here, through a rigorous asymptotic analysis and an accurate numerical solution of the optimized effective-potential integral equation, that the Kohn-Sham exact exchange potential decays as ln(z)/z far into the vacuum side of an extended semi-infinite jellium. In contrast with the situation in localized systems, such as atoms, molecules, and slabs, this dominant contribution does not arise from the so-called Slater potential. This exact exchange result provides a strong constraint on the suitability of approximate correlation-energy functionals.Fil: Horowitz, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Proetto, Cesar Ramon. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Pitarke, J. M.. Consejo Superior de Investigaciones Científicas; Españ
Universal correction for the Becke–Johnson exchange potential
Full text linkThe Becke-Johnson exchange potential [A. D. Becke and E. R. Johnson, J. Chem. Phys. 124, 221101 (2006)] has been successfully used in electronic structure calculations within density-functional theory. However, in its original form, the potential may dramatically fail in systems with non-Coulombic external potentials, or in the presence of external magnetic or electric fields. Here, we provide a system-independent correction to the Becke-Johnson approximation by (i) enforcing its gauge-invariance and (ii) making it exact for any single-electron system. The resulting approximation is then better designed to deal with current-carrying states and recovers the correct asymptotic behavior for systems with any number of electrons. Tests of the resulting corrected exchange potential show very good results for a hydrogen chain in an electric field and for a four-electron harmonium in a magnetic field.Fil: E. Rasanen. Universidad de Jyvaskyla; FinlandiaFil: S. Pittalis. University of Missouri; Estados Unidos. Freie Universität Berlin; Alemania. European Theoretical Spectroscopy Facility; Estados UnidosFil: Proetto, Cesar Ramon. European Theoretical Spectroscopy Facility; Estados Unidos. Freie Universität Berlin; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin
Pseudospin anisotropy of trilayer semiconductor quantum Hall ferromagnets
Full text linkWhen two Landau levels are brought to a close coincidence between them and with the chemical potential in the integer quantum Hall regime, the two Landau levels can just cross or collapse while the external or pseudospin field that induces the alignment changes. In this work, all possible crossings are analyzed theoretically for the particular case of semiconductor trilayer systems, using a variational Hartree-Fock approximation. The model includes tunneling between neighboring layers, bias, intralayer, and interlayer Coulomb interaction among the electrons. We have found that the general pseudospin anisotropy classification scheme used in bilayers applies also to the trilayer situation, with the simple crossing corresponding to an easy-axis ferromagnetic anisotropy analogy, and the collapse case corresponding to an easy-plane ferromagnetic analogy. An isotropic case is also possible, with the levels just crossing or collapsing depending on the filling factor and the quantum numbers of the two nearby levels. While our results are valid for any integer filling factor ν (=1,2,3,...), we have analyzed in detail the crossings at ν=3 and 4, and we have given clear predictions that will help in their experimental search. In particular, the present calculations suggest that by increasing the bias, the trilayer system at these two filling factors can be driven from an easy-plane anisotropy regime to an easy-axis regime, and then can be driven back to the easy-plane regime. This kind of reentrant behavior is a unique feature of the trilayers, compared with the bilayers.Fil: Miravet Martinez, Daniel. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin
Spin-dependent Optimized Effective Potential formalism for open and closed systems
Full text linkOrbital-based exchange (x) correlation (c) energy functionals, leading to the Optimized Effective Potential (OEP) formalism of density-functional theory (DFT), are gaining increasing importance in ground-stateDFT, as applied to the calculation of the electronic structure of closed systems with a fixed number of particles, like atoms and molecules. These types of functionals prove also to be extremely valuable for dealing with solid-state systems with reduced dimensionality, such as is the case ofelectrons trapped at the interface between two different semiconductors, or narrow metallic slabs.In both cases, electrons build a quasi-two-dimensional electron gas, or Q2DEG.We provide here a general DFT-OEP formal scheme valid both for Q2DEG´s either isolated (closed) or in contact with a particle bath (open), and show that both possible representations are equivalent, being the choice of one or the other essentially a question of convenience. Based on this equivalence, a calculation scheme is proposed which avoids the non-invertibility problem of the density response function forclosed systems.We also consider the case of spontaneously spin-polarized Q2DEG´s, and findthat far from the region where the Q2DEG is localized, the exact -only exchange potential approaches two different, spin-dependent asymptotic limits. As an example, besides these formal results, we also provide numerical results for a spin-polarized jellium slab, using the new OEP formalism for closed systems. The accuracy of the Krieger-Li-Iafrate (KLI) approximation has been also tested for the same system, and found to be as good as it is for atoms and molecules.Fil: Rigamonti, Santiago. Humboldt-Universität zu Berlin; AlemaniaFil: Horowitz, Claudio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Proetto, Cesar Ramon. Comisión Nacional de Energía Atomica. Centro Atomico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Exact-exchange density functional theory of the integer quantum Hall effect: strict 2D limit
Full text linkA strict bidimensional (strict-2D) exact-exchange (EE) formalism within the framework of density-functional theory (DFT) has been developed and applied to the case of an electron gas subjected to a strong perpendicular magnetic field, that drives the system to the regime of the integer quantum Hall effect (IQHE). As the filling of the emerging Landau levels proceeds, two main features results: i) the EE energy minimizes with a discontinuous derivative at every integer filling factor ν; and ii) the EE potential display sharp discontinuities at every integer ν. The present contribution provides a natural improvement as compared with the widely used local-spin-density approximation (LSDA), since the EE energy functional fully contains the effect of the magnetic field, and includes an inter-layer exchange coupling for multilayer systems. As a consistency test, the LSDA is derived as the leading term of a low-field expansion of the EE energy and potential.Fil: Miravet Martinez, Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Proetto, Cesar Ramon. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin
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