ABSTRACT
A multi-orbital ionic Hamiltonian is presented to analyze the many-body properties of the d-transition metal atoms. This Hamiltonian considers all the atomic states obeying the first Hund's rule and also includes all orbital degeneracy, as well as the interaction of the atom with a metal. We analyze the solution of this ionic Hamiltonian by means of the equation of Motion method up to the fourth order,V4, in the atom-metal interaction. Equations for the appropriate Green-functions for analyzing the chemical and transport properties of the system are given for different atom occupancies. In particular, we introduce a full analysis of the multi-orbital Hamiltonian including atomic configurations withN, N+ 1 andN- 1 electrons, and discuss its Kondo properties. The shellsd1,d2andd3are analyzed in detail and Kondo energies are deduced in all these cases showing good agreement with the conventional known results.
ABSTRACT
The interaction between a single magnetic atom and the metal environment (including a magnetic field) is analyzed by introducing an ionic Hamiltonian combined with an effective crystal-field term, and by using a Green-function equation of motion method. This approach describes the inelastic electron tunneling spectroscopy and the Kondo resonances as due to atomic spin fluctuations associated with electron co-tunneling processes between the leads and the atom. We analyze in the case of Fe on CuN the possible spin fluctuations between states with S = 2 and 3/2 or 5/2 and conclude that the experimentally found asymmetries in the conductance with respect to the applied bias, and its marked structures, are well explained by the 2â3/2 spin fluctuations. The case of Co is also considered and shown to present, in contrast with Fe, a resonance at the Fermi energy corresponding to a Kondo temperature of 6 K.
ABSTRACT
The neutral to negative charge fluctuation of a hydrogen atom in front of a graphene surface is calculated by using the Anderson model within an infinite intra atomic Coulomb repulsion approximation. We perform an ab initio calculation of the Anderson hybridization function that allows investigation of the effect of quantum-mechanical interference related to the Berry phase inherent to the graphene band structure. We find that consideration of the interaction of hydrogen on top of many C atoms leads to a marked asymmetry of the imaginary part of the hybridization function with respect to the Fermi level. Consequently, Fano factors larger than one and strongly dependent on the energy around the Fermi level are predicted. Moreover, the suppression of the hybridization for energies above the Fermi level can explain the unexpected large negative ion formation measured in the scattering of protons by graphite-like surfaces.
ABSTRACT
The resonant charge exchange between atoms and surfaces is described by considering a localized atomistic view of the solid within the Anderson model. The presence of a surface energy gap is treated within a simplified tight-binding model of the solid, and a proper calculation of the Hamiltonian terms based on a LCAO expansion of the solid eigenstates is performed. It is found that interference terms jointly with a surface projected gap maximum at the Γ point and the Fermi level inside it, lead to hybridization widths negligible around the Fermi level. This result can explain experimental observations related to long-lived adsorbate states and anomalous neutral fractions of low energy ions in alkali/Cu(111) systems.
ABSTRACT
A controversy about the conductance through single atoms still exists. There are many experiments where values lower than the quantum unity G(0) = 2e(2)/h have been found associated to Kondo regimes with high Kondo temperatures. Specifically in the Pd single atom contact, conductance values close to G(0)/2 at room temperature have been reported. In this work we propose a theoretical analysis of a break junction of Pd where the charge fluctuation in the single atom contact is limited to the most probable one: [Formula: see text]. The projected density of states and the characteristics of the electron transport are calculated by using a realistic description of the interacting system. A Kondo regime is found where the conductance values and their dependence on temperature are in good agreement with the experimental trends observed in the conduction of single molecule transistors based on transition metal coordination complexes.
ABSTRACT
We report on measurements of electron emission spectra from surfaces of highly oriented pyrolytic graphite (HOPG) excited by 1-5 keV He+ and Li+ which, for He+, exhibit a previously unreported high-energy structure. Through a full quantum dynamic description that allows for the calculation of neutralization and electron-hole pair excitation, we show that these high-energy electrons can arise from autoionization of excitons formed by electron promotion to conduction band states close to the vacuum level. The same calculation explains the observed absence of high-energy excitons for Li+ on HOPG.
ABSTRACT
Blood biochemistry, body composition, and resting energy expenditure were studied in 25 patients with anorexia nervosa admitted to hospital during a period of 18 months. The patients' ages ranged from 12.9 to 17.2 years, and the abnormal feeding history from 3 to 12 months. Blood chemistry values were in the normal range, but fat body mass and lean body mass were reduced and extracellular water volume was expanded beyond normal values. Resting energy expenditure was reduced to 49% to 91% of values predicted by the Harris-Benedict equations. Substrate use after overnight fast indicated an abnormally high use of carbohydrates. Significant correlations were found between extracellular water volume and triceps skin-fold thickness, mid-arm muscle circumference and lean body mass, and substrate use and weight loss as a percentage of initial weight. We suggest that these simple anthropometric measurements can be used to assess and monitor the refeeding of patients with anorexia nervosa.
Subject(s)
Anorexia Nervosa/physiopathology , Body Composition , Energy Metabolism , Adolescent , Anorexia Nervosa/pathology , Anthropometry , Body Water , Child , Female , Humans , Male , Skinfold ThicknessABSTRACT
Changes in body composition were studied in 13 girls with anorexia nervosa before and during 2 months of refeeding. Fat body mass and fat-free body mass were derived from skin-fold measurements. Total body potassium was measured by whole body counter, and intracellular water was calculated from it. Extracellular water was measured as the bromide space after oral bromide administration. A gradual increase was noted in weight, fat body mass, fat-free body mass, and total body potassium during refeeding. Extracellular water was expanded on admission and increased in all patients in the first weeks of treatment; later it fell to normal. Most of the changes in fat-free body mass over the first weeks of refeeding could be accounted for by an expansion in extracellular water. Particular care must therefore be taken with fluid balance during the first few weeks of refeeding.
Subject(s)
Anorexia Nervosa/diet therapy , Body Composition , Adipose Tissue , Adolescent , Body Water , Child , Extracellular Space , Female , Humans , Intracellular Fluid , Potassium/analysisABSTRACT
Concentrations of chlorinated hydrocarbons in airborne dust carried by the trade winds from the European-African land areas to Barbados range from less than 1 to 164 parts per billion. The lower limit of the average content of 1 cubic meter of air is 7.8 x 10-(14) gram. The contributions of river-borne and atmospherically transported pesticides to parts of the marine environment are calculated approximately and comtpared. The amnounts of pesticides contributed to the tropical Atlantic by the trade winds appear to be comparable to those carried to the sea by major river systems.