Self‐consistent intermediate Hamiltonians : A coupled cluster type formulation of the singles and doubles configuration interaction matrix dressing

This paper presents a new self‐consistent dressing of a singles and doubles configuration interaction matrix which insures size‐consistency, separability into closed‐shell subsystems if localized molecular orbitals (MOs) are used, and which includes all fourth order corrections. This method yields, among several schemes, a reformulation of the coupled cluster method, including fully the cluster operators of single and double excitations, and partially those of the triples (Bartlett’s algorithm named CCSDT‐1a). Further improvement can be easily included by adding exclusion principle violating corrections. Since it leads to a matrix diagonalization, the method behaves correctly in case of near degeneracies between the reference determinant and some doubles. Due to its flexibility this formulation offers the possibility of consistent combination with less expensive treatments for the study of very large [email protected] ; [email protected]

Many-body-QED perturbation theory: Connection to the Bethe-Salpeter equation

The connection between many-body theory (MBPT)--in perturbative and non-perturbative form--and quantum-electrodynamics (QED) is reviewed for systems of two fermions in an external field. The treatment is mainly based upon the recently developed covariant-evolution-operator method for QED calculations [Lindgren et al. Phys. Rep. 389, 161 (2004)], which has a structure quite akin to that of many-body perturbation theory. At the same time this procedure is closely connected to the S-matrix and the Green's-function formalisms and can therefore serve as a bridge between various approaches. It is demonstrated that the MBPT-QED scheme, when carried to all orders, leads to a Schroedinger-like equation, equivalent to the Bethe-Salpeter (BS) equation. A Bloch equation in commutator form that can be used for an "extended" or quasi-degenerate model space is derived. It has the same relation to the BS equation as has the standard Bloch equation to the ordinary Schroedinger equation and can be used to generate a perturbation expansion compatible with the BS equation also for a quasi-degenerate model space.Comment: Submitted to Canadian J of Physic

Relativistic quantum dynamics in strong fields: Photon emission from heavy, few-electron ions

Recent progress in the study of the photon emission from highly-charged heavy ions is reviewed. These investigations show that high-$Z$ ions provide a unique tool for improving the understanding of the electron-electron and electron-photon interaction in the presence of strong fields. Apart from the bound-state transitions, which are accurately described in the framework of Quantum Electrodynamics, much information has been obtained also from the radiative capture of (quasi-) free electrons by high-$Z$ ions. Many features in the observed spectra hereby confirm the inherently relativistic behavior of even the simplest compound quantum systems in Nature.Comment: Version 18/11/0

Sequential decoupling of negative-energy states in Douglas-Kroll-Hess theory

Here, we review the historical development, current status, and prospects of Douglas--Kroll--Hess theory as a quantum chemical relativistic electrons-only theory.Comment: 15 page

DFT rationalization of the room-temperature luminescence properties of Ru(bpy) 3 2+ and Ru(tpy) 2 2+ : 3MLCT–3MC minimum energy path from NEB calculations and emission spectra from VRES calculations

Published as part of the special collection of articles “CHITEL 2017—Paris—France”.International audienceExtensive experimental data covering 40 years of research are available on Ru(bpy) 3 2+ and Ru(tpy) 2 2+ , which are the archetypes of inorganic photochemistry. The last decade has enabled computational chemists to tackle this topic through density functional theory and to shed some new light on our old friends. For the first time, this theoretical study maps the minimum energy path linking the 3 MLCT (metal-to-ligand charge transfer) and the 3 MC (metal centred) states with the nudged elastic band (NEB) method, also providing the calculation of the corresponding energy barrier. Remarkably, the obtained data are in very good agreement with the experimental activation energies reported from variable temperature luminescence measurements. Calculation of vibrationally resolved electronic spectra (VRES) is also in excellent agreement with the experimental emission maximum and bandshape of Ru(bpy) 3 2+. Additionally, the 3 MC-GS minimum energy crossing point (MECP) was optimized for each complex. The combination of these data rationalizes the room-temperature luminescence of the bpy complex and non-luminescence of the tpy complex

An evaluation of the density functional approach in the zero order regular approximation for relativistic effects: Magnetic interactions in small metal compounds

The density functional approach was evaluated for electron spin resonance (ESR) parameters in the relativistic zero order regular approximation in small metal compounds. The effects of spin-orbit coupling and spin polarization on the magnetic hyperfine interaction were investigated. It was shown that relativistic effects in the calculation of the hyperfine parameters were large not only for the heavy metals but also for ligands bound to heavy elements due to secondary effects

Structural and optical properties of a neutral Nickel bisdithiolene complex: density functional versus ab initio methods

International audienceDensity functional theory (DFT) and ab initio computations are applied to examine different properties of diamagnetic, square planar neutral nickel complexes that contain two bidentate ligands derived from bis ((ethylene)-1,2-dithiolato) ligands. Geometry, vibrational spectra (IR and Raman) are well reproduced in the density functional framework whereas TD-DFT methods are clearly insufficient to reproduce absorption properties. Multiconfigurational perturbation theory based on a complete active space self-consistent field wave function, i.e. MRPT2 and MRPT4 methods, reveal the pronounced multiconfigurational character of the ground state wave function. The singlet-triplet energy gap, the energy gained from symmetry breaking and the singlet diradical character are discussed in the DFT and ab initio frameworks. The complex of interest does not display a strong singlet diradical character. This molecule having a peculiar electronic structure; strong delocalization as shown by a new electron pair localization function analysis (EPLF); exemplifies the fragility of the TD-DFT method and thus, caution should be taken in the determination of the energetic properties of such compound

Improved theory of laser-enhanced ionization in flames: comparison with experiment

An improved theory for laser enhanced ionization in flames has been developed for one‐ and two‐step laser excitations. The model gives an analytical expression for the sensitivity of the method for a given transition of any element. The theoretical expression is compared with experimentally measured signals for a number of elements and the agreement is found to be generally good

MAPAS CONCEITUAIS COMO FERRAMENTA DE DIVULGAÇÃO CIENTÍFICA NA FORMAÇÃO DE PROFESSORES DE FÍSICA

Based on Ausubel's Theory of Meaningful Learning, this article proposes and discusses the use of concept maps in the scientific dissemination of research topics in Physics, in the training of teachers in a class of the 4th period of the Degree in Physics. Aiming to assess students' understanding of advanced topics such as Particle Physics, Condensed Matter, Quantum Computing, Nuclear Physics, Astronomy and Medical Physics, in order to investigate how complex concepts are assimilated and contextualized within the cognitive structure of students.Com base na Teoria da aprendizagem significativa de Ausubel, este artigo propõe e discute a utilização de mapas conceituais na divulgação científica de tópicos de pesquisa em Física, na formação de professores em uma turma do 4º período do curso de Licenciatura em Física. Tendo como objetivos avaliar o entendimento dos estudantes acerca de temas avançados como a Física de partículas, Matéria Condensada, Computação Quântica, Física Nuclear, Astronomia e Física Médica, de modo a investigar a forma como conceitos complexos são assimilados e contextualizados dentro da estrutura cognitiva dos alunos