Full-Potential LMTO: Total Energy and Force Calculations

The essential features of a full potential electronic structure method using Linear Muffin-Tin Orbitals (LMTOs) are presented. The electron density and potential in the this method are represented with no inherent geometrical approximation. This method allows the calculation of total energies and forces with arbitrary accuracy while sacrificing much of the efficiency and physical content of approximate methods such as the LMTO-ASA method.Comment: 25 pages, 2 figures, Workshop on the TB-LMTO method, Monastery of Mont St. Odile, October 4-5, 199

Etude spectroscopique de metaux et de composes intermetalliques binaires par la methode L.M.T.O

CNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

EFFETS DES CORRELATIONS SUR LES PROPRIETES ELECTRONIQUES ET OPTIQUES DES SEMICONDUCTEURS ET ISOLANTS

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Etude ab-initio des propriétés électroniques, optiques et du transport électronique dans les nanotubes de carbone

Ce travail a pour objectif la compréhension des effets des impuretés sur les propriétés électroniques et de transport électronique des nanotubes de carbones monoparois. Dans la première partie nous avons étudié l'effet du dopage substitutionnel par des atomes de bore, d azote ou de silicium sur la structure électronique des nanotubes de carbone pour différents diamètres, dans le but de déterminer la dépendance de la réactivité chimique en fonction de la courbure des nanotubes. Puis nous avons étudié la distribution des impuretés en fonction de la chiralité des nanotubes, et le comportement des spectres optiques en fonction du diamètre et de la chiralité des nanotubes en présence d impuretés. Dans la deuxième partie, nous avons utilisé le formalisme de la fonction de Green hors-équilibre pour mieux comprendre les propriétés de transport électronique des nanotubes de carbone. Il s agit de calculer la conductance électrique d un nanotube dans lequel est insérée, ou sur lequel est adsorbée, une molécule organique. Pour déterminer l adsorption de la molécule sur la surface du nanotube, nous avons calculé l énergie totale en tenant compte des forces de dispersion de van der Waals. Nous avons également étudié l effet des liaisons chimiques polarisées en spins à l interface des jonctions Fe(100)- nanotube par contact direct sur les propriétés de conduction des nanotubes zigzag et armchair de différentes tailles.The objective of this work is to understand the effects of impurities on the electronic and transport properties of single wall carbon nanotubes. In the first part, we studied the effect of substitutional doping by boron, nitrogen or silicon atoms on the electronic structure of carbon nanotubes for different diameters in order to determine the chemical reactivity as a function of the nanotube curvature. We then studied the impurity distribution as a function of the nanotube chirality and the behavior of the optical spectra as a function of the diameter and the chirality of the nanotubes and as a function of the impurity distribution. In a second part, we used the nonequilibrium Green s function to understand the electronic transport of carbon nanotubes. This is to calculate the electric conductance of a single nanotube in which an organic molecule is either inserted or adsorbed on its surface. To determine the adsorption of the molecule we calculated the total energy, taking into account the dispersive forces of van der Waals. We also studied the effect of spin polarized chemical bonding at the interface of the Fe(001)-nanotube direct junctions on the electronic transport of zigzag and armchair nanotubes of different sizes.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Inverse spin crossover in fluorinated Fe(1,10-phenanthroline) 2 (NCS) 2 adsorbed on Cu (001) surface

Density functional theory (DFT) including van der Waals weak interaction in conjunction with the so called rotational invariant DFT+U, where is the Hubbard interaction of the iron site, is used to show that the fluorinated spin crossover Fe(phen)(NCS) molecule whether in the gas phase or adsorbed on Cu(001) surface switches from the original low spin state to the high spin state. The calculated minimal energy path by means of both the nudged elastic band method and the constrained minimization method is found to be smaller for the fluorinated molecule. Using Bader electron density analysis and a point charge model, this inversion of the spin crossover is explained in terms of electron doping of the Fe-octahedron cage which led to an increase of the Fe–N bond lengths and the distortion of the Fe(II) octahedron. Consequently, the ligand-field splitting is drastically reduced, making the high-spin ground state more stable than the low-spin state. The calculated scanning tunneling microscopy (STM) images in the Tersoff–Hamann approximation show a clear distinction between the fluorinated and the unfluorinated molecule. This theoretical prediction is awaiting future STM experimental confirmation

When Molecular Dimerization Induces Magnetic Bi‐Stability at the Metal–Organic Interface

Abstract 2D metal–organic frameworks have been recently proposed as a flexible platform for realizing new functional materials including quantum phases. Here, we present a method to create metal‐organic dimer complexes by on‐surface assembly on a metal substrate using low‐temperature scanning tunneling microscopy (STM) and spectroscopy (STS). We demonstrate that a dimer of Mn‐Phthalocyanine (MnPc)2 on a Ag(111) surface can be switched between two stable configurations upon a small conformational change controlled by STM manipulation. By means of density‐functional theory calculations, it is found that the two conformations correspond to an antiferromagnetic (AFM) and a ferromagnetic (FM) state respectively. Directly coordinated Mn atoms of the dimer lead to an AFM‐coupling whereas indirectly coordinated (shifted) Mn atoms lead to a FM‐coupling. Rarely seen in a molecular‐dimers with transition‐metal atoms, the FM‐AFM‐FM transition is thus readily on‐surface accessible. Furthermore, the two configurations of the switch are easily identified by their Kondo states, opening interesting routes in terms of both, writing (FM versus AFM states) and reading. These results pave the experimental route toward dimer‐based materials with complex magnetic structures of potential interest for application in spintronics, logics and computing

Theory of x-ray absorption spectroscopy for ferrites

The theoretical calculation of the interaction of electromagnetic radiation with matter remains a challenging problem for contemporary ab initio electronic structure methods, in particular, for x-ray spectroscopies. This is not only due to the strong interaction between the core hole and the photoexcited electron, but also due to the elusive multiplet effects that arise from the Coulomb interaction among the valence electrons. In this work we report a method based on density functional theory in conjunction with multiplet ligand-field theory to investigate various core-level spectroscopies, in particular, x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The developed computational scheme is applied to the L 2 , 3 XAS and XMCD edges of magnetite (Fe 3 O 4 ) as well as cobalt ferrite (CoFe 2 O 4 ) and nickel ferrite (NiFe 2 O 4 ). The results are in overall good agreement with experimental observations, both regarding the XAS L 2 / L 3 branching ratio, the peak positions, as well as the relative intensities. The agreement between theory and experiment is equally good for XAS and the XMCD spectra, for all studied systems. The results are analyzed in terms of e g and t 2 g orbital contribution, and the robustness of the spectra with regard to the uncertainties of the Slater parameters is investigated. The analysis also highlights the strong effect of the 2 p -3 d interaction in x-ray spectroscopy

Full-Potential Electronic Structure Method: Energy and Force Calculations with Density Functional and Dynamical Mean Field Theory

This book covers the theory of electronic structure of materials, with special emphasis on the usage of linear muffin-tin orbitals. Methodological aspects are given in detail as are examples of the method when applied to various materials. Different exchange and correlation functionals are described and how they are implemented within the basis of linear muffin-tin orbitals. Functionals covered are the local spin density approximation, generalised gradient approximation, self-interaction correction and dynamical mean field theory

In Situ Pseudopotentials for Electronic Structure Theory

We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn-Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn-Sham equation, to extract the pseudopotential that produces the state generated in steps i-iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na