Melting of Xenon to 80 GPa, p-d hybridization, and an ISRO liquid

Measurements made in a laser heated diamond-anvil cell are reported that extend the melting curve of Xe to 80 GPa and 3350 K. The steep lowering of the melting slope (dT/dP) that occurs near 17 GPa and 2750 K results from the hybridization of the p-like valence and d-like conduction states with the formation of clusters in the liquid having Icosahedral Short-Range Order (ISRO)

Structural and Magnetic Properties of Trigonal Iron

First principles calculations of the electronic structure of trigonal iron were performed using density function theory. The results are used to predict lattice spacings, magnetic moments and elastic properties; these are in good agreement with experiment for both the bcc and fcc structures. We find however, that in extracting these quantities great care must be taken in interpreting numerical fits to the calculated total energies. In addition, the results for bulk iron give insight into the properties of thin iron films. Thin films grown on substrates with mismatched lattice constants often have non-cubic symmetry. If they are thicker than a few monolayers their electronic structure is similar to a bulk material with an appropriately distorted geometry, as in our trigonal calculations. We recast our bulk results in terms of an iron film grown on the (111) surface of an fcc substrate, and find the predicted strain energies and moments accurately reflect the trends for iron growth on a variety of substrates.Comment: 11 pages, RevTeX,4 tar'd,compressed, uuencoded Postscript figure

Emergence of Strong Exchange Interaction in the Actinide Series: The Driving Force for Magnetic Stabilization of Curium

Using electron energy-loss spectroscopy in a transmission electron microscope, many-electron atomic spectral calculations and density functional theory, we examine the electronic and magnetic structure of Cm metal. We show that angular momentum coupling in the 5f states plays a decisive role in the formation of the magnetic moment. The 5f states of Cm in intermediate coupling are strongly shifted towards the LS coupling limit due to exchange interaction, unlike most actinide elements where the effective spin-orbit interaction prevails. It is this LS-inclined intermediate coupling that is the key to producing the large spin polarization which in turn dictates the newly found crystal structure of Cm under pressure

The stabilizing role of itinerant ferromagnetism in inter-granular cohesion in iron

We present a simple, general energy functional for ferromagnetic materials based upon a local spin density extension to the Stoner theory of itinerant ferromagnetism. The functional reproduces well available ab initio results and experimental interfacial energies for grain boundaries in iron. The model shows that inter-granular cohesion along symmetric tilt boundaries in iron is dependent upon strong magnetic structure at the interface, illuminates the mechanisms underlying this structure, and provides a simple explanation for relaxation of the atomic structure at these boundaries.Comment: In review at Phys. Rev. Lett. Submitted 23 September 1997; revised 16 March 199

Modelling charge self-trapping in wide-gap dielectrics: Localization problem in local density functionals

We discuss the adiabatic self-trapping of small polarons within the density functional theory (DFT). In particular, we carried out plane-wave pseudo-potential calculations of the triplet exciton in NaCl and found no energy minimum corresponding to the self-trapped exciton (STE) contrary to the experimental evidence and previous calculations. To explore the origin of this problem we modelled the self-trapped hole in NaCl using hybrid density functionals and an embedded cluster method. Calculations show that the stability of the self-trapped state of the hole drastically depends on the amount of the exact exchange in the density functional: at less than 30% of the Hartree-Fock exchange, only delocalized hole is stable, at 50% - both delocalized and self-trapped states are stable, while further increase of exact exchange results in only the self-trapped state being stable. We argue that the main contributions to the self-trapping energy such as the kinetic energy of the localizing charge, the chemical bond formation of the di-halogen quasi molecule, and the lattice polarization, are represented incorrectly within the Kohn-Sham (KS) based approaches.Comment: 6 figures, 1 tabl

Capabilities for Testing the Electronic Configuration in Pu

The benchmarking of theoretical modeling is crucial to the ultimate determination of the nature of the electronic structure of Pu. Examples of experimental techniques used for cross checking state of the art calculations will be given

Quantum-based Atomistic Simulation of Transition Metals

First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in d-electron transition metals within density-functional quantum mechanics. In mid-period bcc metals, where multi-ion angular forces are important to structural properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions of pressure and temperature. Recent algorithm improvements have also led to a more general matrix representation of MGPT beyond canonical bands allowing increased accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed, and the current development of temperature-dependent potentials

On the electronic configuration in Pu: spectroscopy and theory

Photoelectron spectroscopy, synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy, and density-functional calculations within the mixed-level and magnetic models, together with canonical band theory have been used to study the electron configuration in Pu. These methods suggest a 5f{sup n} configuration for Pu of 5 {le} n < 6, with n {ne} 6, contrary to what has recently been suggested in several publications. We show that the n = 6 picture is inconsistent with the usual interpretation of photoemission and x-ray absorption spectra. Instead, these spectra support the traditional conjecture of a 5f{sup 5} configuration in Pu as is obtained by density-functional theory. We further argue, based on 5f-band filling, that an n = 6 hypothesis is incompatible with the position of Pu in the actinide series and its monoclinic ground-state phase

Implementation of an evidence-based guideline on fluid resuscitation: lessons learnt for future guidelines

There is little experience with the nationwide implementation of an evidence-based pediatric guideline on first-choice fluid for resuscitation in hypovolemia. We investigated fluid prescribing behavior at (1) guideline development, (2) after guideline development, and (3) after active implementation and identified potential barriers and facilitators for guideline implementation. In order to minimize costs and to optimize implementation effect, we continuously developed and adjusted implementation strategies according to identified barriers. Implementation success was evaluated using questionnaires, pharmaceutical data, and data from medical records. The most remarkable change occurred after guideline development and dissemination: Normal saline use by neonatologists increased from 22-89% to 100% and by pediatric intensivists from 43-71% to 88-100%, and synthetic colloid use by pediatric intensivists declined from 29-43% to 0-13% with a reduction in albumin use by neonatologists from 11-44% to 0%. After active guideline implementation, most of specialist's management behavior was according to the guideline. Stakeholders involved in the developmental process are of great importance in disseminating recommendations before active implementation. Therefore, to successfully implement guidelines and reduce costs of active implementation, any guideline development should consider implementation right from the beginning. Implementation strategies should target identified barriers and will therefore always be guideline specifi