2,191 research outputs found

    Correlation consistent valence basis sets for use with the Stuttgart-Dresden-Bonn relativistic effective core potentials: the atoms Ga-Kr and In-Xe

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    We propose large-core correlation-consistent pseudopotential basis sets for the heavy p-block elements Ga-Kr and In-Xe. The basis sets are of cc-pVTZ and cc-pVQZ quality, and have been optimized for use with the large-core (valence-electrons only) Stuttgart-Dresden-Bonn relativistic pseudopotentials. Validation calculations on a variety of third-row and fourth-row diatomics suggest them to be comparable in quality to the all-electron cc-pVTZ and cc-pVQZ basis sets for lighter elements. Especially the SDB-cc-pVQZ basis set in conjunction with a core polarization potential (CPP) yields excellent agreement with experiment for compounds of the later heavy p-block elements. For accurate calculations on Ga (and, to a lesser extent, Ge) compounds, explicit treatment of 13 valence electrons appears to be desirable, while it seems inevitable for In compounds. For Ga and Ge, we propose correlation consistent basis sets extended for (3d) correlation. For accurate calculations on organometallic complexes of interest to homogenous catalysis, we recommend a combination of the standard cc-pVTZ basis set for first- and second-row elements, the presently derived SDB-cc-pVTZ basis set for heavier p-block elements, and for transition metals, the small-core [6s5p3d] Stuttgart-Dresden basis set-RECP combination supplemented by (2f1g) functions with exponents given in the Appendix to the present paper

    Quantitative study of valence and configuration interaction parameters of the Kondo semiconductors CeM2Al10 (M = Ru, Os and Fe) by means of bulk-sensitive hard x-ray photoelectron spectroscopy

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    The occupancy of the 4f^n contributions in the Kondo semiconductors CeM2Al10(M = Ru, Os and Fe) has been quantitatively determined by means of bulk-sensitive hard x-ray photoelectron spectroscopy (HAXPES) on the Ce 3d core levels. Combining a configuration interaction scheme with full multiplet calculations allowed to accurately describe the HAXPES data despite the presence of strong plasmon excitations in the spectra. The configuration interaction parameters obtained from this analysis -- in particular the hybridization strength V_eff and the effective f binding energy Delta_f -- indicate a slightly stronger exchange interaction in CeOs2Al10 compared to CeRu2Al10, and a significant increase in CeFe2Al10. This verifies the coexistence of a substantial amount of Kondo screening with magnetic order and places the entire CeM2Al10 family in the region of strong exchange interactions.Comment: 9 pages, 4 figures, submitted to Physical Review

    CeRu4_4Sn6_6: a strongly correlated material with nontrivial topology

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    Topological insulators form a novel state of matter that provides new opportunities to create unique quantum phenomena. While the materials used so far are based on semiconductors, recent theoretical studies predict that also strongly correlated systems can show non-trivial topological properties, thereby allowing even the emergence of surface phenomena that are not possible with topological band insulators. From a practical point of view, it is also expected that strong correlations will reduce the disturbing impact of defects or impurities, and at the same increase the Fermi velocities of the topological surface states. The challenge is now to discover such correlated materials. Here, using advanced x-ray spectroscopies in combination with band structure calculations, we infer that CeRu4_4Sn6_6 is a strongly correlated material with non-trivial topology.Comment: 10 pages, 6 figures, submitted to Scientific Report

    Antiferromagnetic correlations in strongly valence fluctuating CeIrSn

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    CeIrSn with a quasikagome Ce lattice in the hexagonal basal plane is a strongly valence fluctuating compound, as we confirm by hard x-ray photoelectron spectroscopy and inelastic neutron scattering, with a high Kondo temperature of TK480T_{\mathrm{K}}\sim 480\,K. We report a negative in-plane thermal expansion α/T\alpha/T below 2\,K, which passes through a broad minimum near 0.75\,K. Volume and aa-axis magnetostriction for BaB \parallel a are markedly negative at low fields and change sign before a sharp metamagnetic anomaly at 6\,T. These behaviors are unexpected for Ce-based intermediate valence systems, which should feature positive expansivity. Rather they point towards antiferromagnetic correlations at very low temperatures. This is supported by muon spin relaxation measurements down to 0.1\,K, which provide microscopic evidence for a broad distribution of internal magnetic fields. Comparison with isostructural CeRhSn suggests that these antiferromagnetic correlations emerging at TTKT\ll T_{\mathrm{K}} result from geometrical frustration.Comment: to be published in Phys. Rev. Let

    Optimal control theory for unitary transformations

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    The dynamics of a quantum system driven by an external field is well described by a unitary transformation generated by a time dependent Hamiltonian. The inverse problem of finding the field that generates a specific unitary transformation is the subject of study. The unitary transformation which can represent an algorithm in a quantum computation is imposed on a subset of quantum states embedded in a larger Hilbert space. Optimal control theory (OCT) is used to solve the inversion problem irrespective of the initial input state. A unified formalism, based on the Krotov method is developed leading to a new scheme. The schemes are compared for the inversion of a two-qubit Fourier transform using as registers the vibrational levels of the X1Σg+X^1\Sigma^+_g electronic state of Na2_2. Raman-like transitions through the A1Σu+A^1\Sigma^+_u electronic state induce the transitions. Light fields are found that are able to implement the Fourier transform within a picosecond time scale. Such fields can be obtained by pulse-shaping techniques of a femtosecond pulse. Out of the schemes studied the square modulus scheme converges fastest. A study of the implementation of the QQ qubit Fourier transform in the Na2_2 molecule was carried out for up to 5 qubits. The classical computation effort required to obtain the algorithm with a given fidelity is estimated to scale exponentially with the number of levels. The observed moderate scaling of the pulse intensity with the number of qubits in the transformation is rationalized.Comment: 32 pages, 6 figure

    Determinación de daño genético en comerciantes de plaguicidas en el departamento de Matagalpa

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    EL DAÑO CITOGENÉTICO ASOCIADO CON PLAGUICIDAS POR PARTE de comerciantes de agroquímicos fue evaluado en el departamento de Matagalpa analizando micronúcleos en células bucales (MNBC). Así mismo, fue evaluada la exposición crónica a plaguicidas usando la prueba de acetilcolinesterasa y adicionalmente se identificaron mutaciones de manera exploratoria en el gen CYP2D6, implicado en el metabolismo de plaguicidas. La comparación entre comerciantes de plaguicidas y controles reveló diferencias significativas en las frecuencias de MNBC (6.23±2.2 vs. 3.63±1.3 MN/2000 MNBC, P<0.001, t de student). Niveles de colinesterasa indican efecto neurotóxico crónico en los comerciantes de plaguicidas. Estos comerciantes utilizan poco o ningún equipo de protección personal así como medidas de seguridad. Este es el primer estudio a nivel nacional que reporta efecto citogenético de exposición crónica a plaguicidas en comerciantes expuestos
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