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DDC: 550 × Subject: Electronic structure ×

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    Measurement of Spin Dynamics in a Layered Nickelate Using X-Ray Photon Correlation Spectroscopy: Evidence for Intrinsic Destabilization of Incommensurate Stripes at Low Temperatures
    (College Park, Md. : APS, 2021) Ricci, Alessandro; Poccia, Nicola; Campi, Gaetano; Mishra, Shrawan; Müller, Leonard; Joseph, Boby; Shi, Bo; Zozulya, Alexey; Buchholz, Marcel; Trabant, Christoph; Lee, James C. T.; Viefhaus, Jens; Goedkoop, Jeroen B.; Nugroho, Agustinus Agung; Braden, Markus; Roy, Sujoy; Sprung, Michael; Schüßler-Langeheine, Christian
    We study the temporal stability of stripe-type spin order in a layered nickelate with x-ray photon correlation spectroscopy and observe fluctuations on timescales of tens of minutes over a wide temperature range. These fluctuations show an anomalous temperature dependence: they slow down at intermediate temperatures and speed up on both heating and cooling. This behavior appears to be directly connected with spatial correlations: stripes fluctuate slowly when stripe correlation lengths are large and become faster when spatial correlations decrease. A low-temperature decay of nickelate stripe correlations, reminiscent of what occurs in cuprates as a result of a competition between stripes and superconductivity, hence occurs via loss of both spatial and temporal correlations.
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    Accurate molecular van der Waals interactions from ground-state electron density and free-atom reference data
    (College Park, Md. : APS, 2009) Tkatchenko, Alexandre; Scheffler, Matthias
    We present a parameter-free method for an accurate determination of long-range van der Waals interactions from mean-field electronic structure calculations. Our method relies on the summation of interatomic C6 coefficients, derived from the electron density of a molecule or solid and accurate reference data for the free atoms. The mean absolute error in the C6 coefficients is 5.5% when compared to accurate experimental values for 1225 intermolecular pairs, irrespective of the employed exchange-correlation functional. We show that the effective atomic C6 coefficients depend strongly on the bonding environment of an atom in a molecule. Finally, we analyze the van der Waals radii and the damping function in the C6R-6 correction method for density-functional theory calculations. © 2009 The American Physical Society.