Showing papers in "Journal of Physics: Condensed Matter in 2002"

First-principles simulation: ideas, illustrations and the CASTEP code

Abstract: First-principles simulation, meaning density-functional theory calculations with plane waves and pseudopotentials, has become a prized technique in condensed-matter theory. Here I look at the basics of the suject, give a brief review of the theory, examining the strengths and weaknesses of its implementation, and illustrating some of the ways simulators approach problems through a small case study. I also discuss why and how modern software design methods have been used in writing a completely new modular version of the CASTEP code.

The SIESTA method for ab initio order-N materials simulation

Abstract: We have developed and implemented a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals. Exchange and correlation are treated with the local spin density or generalized gradient approximations. The basis functions and the electron density are projected on a real-space grid, in order to calculate the Hartree and exchange-correlation potentials and matrix elements, with a number of operations that scales linearly with the size of the system. We use a modified energy functional, whose minimization produces orthogonal wavefunctions and the same energy and density as the Kohn-Sham energy functional, without the need for an explicit orthogonalization. Additionally, using localized Wannier-like electron wavefunctions allows the computation time and memory required to minimize the energy to also scale linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.

A second-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons

Abstract: A second-generation potential energy function for solid carbon and hydrocarbon molecules that is based on an empirical bond order formalism is presented. This potential allows for covalent bond breaking and forming with associated changes in atomic hybridization within a classical potential, producing a powerful method for modelling complex chemistry in large many-atom systems. This revised potential contains improved analytic functions and an extended database relative to an earlier version (Brenner D W 1990 Phys. Rev. B 42 9458). These lead to a significantly better description of bond energies, lengths, and force constants for hydrocarbon molecules, as well as elastic properties, interstitial defect energies, and surface energies for diamond.

Surface-enhanced Raman scattering and biophysics

Abstract: Surface-enhanced Raman scattering (SERS) is a spectroscopic technique which combines modern laser spectroscopy with the exciting optical properties of metallic nanostructures, resulting in strongly increased Raman signals when molecules are attached to nanometre-sized gold and silver structures. The effect provides the structural information content of Raman spectroscopy together with ultrasensitive detection limits, allowing Raman spectroscopy of single molecules. Since SERS takes place in the local fields of metallic nanostructures, the lateral resolution of the technique is determined by the confinement of the local fields, which can be two orders of magnitude better than the diffraction limit. Moreover, SERS is an analytical technique, which can give information on surface and interface processes. SERS opens up exciting opportunities in the field of biophysical and biomedical spectroscopy, where it provides ultrasensitive detection and characterization of biophysically/biomedically relevant molecules and processes as well as a vibrational spectroscopy with extremely high spatial resolution. The article briefly introduces the SERS effect and reviews contemporary SERS studies in biophysics/biochemistry and in life sciences. Potential and limitations of the technique are briefly discussed.

Pyroelectric properties of Al(In)GaN/GaN hetero- and quantum well structures

Abstract: The macroscopic nonlinear pyroelectric polarization of wurtzite AlxGa1-xN, InxGa1-xN and AlxIn1-xN ternary compounds (large spontaneous polarization and piezoelectric coupling) dramatically affects the optical and electrical properties of multilayered Al(In)GaN/GaN hetero-, nanostructures and devices, due to the huge built-in electrostatic fields and bound interface charges caused by gradients in polarization at surfaces and heterointerfaces. Models of polarization-induced effects in GaN-based devices so far have assumed that polarization in ternary nitride alloys can be calculated by a linear interpolation between the limiting values of the binary compounds. We present theoretical and experimental evidence that the macroscopic polarization in nitride alloys is a nonlinear function of strain and composition. We have applied these results to interpret experimental data obtained in a number of InGaN/GaN quantum wells?(QWs) as well as AlInN/GaN and AlGaN/GaN transistor structures. We find that the discrepancies between experiment and ab initio theory present so far are almost completely eliminated for the AlGaN/GaN-based heterostructures when the nonlinearity of polarization is accounted for. The realization of undoped lattice-matched AlInN/GaN heterostructures further allows us to prove the existence of a gradient in spontaneous polarization by the experimental observation of two-dimensional electron gases?(2DEGs). The confinement of 2DEGs in InGaN/GaN QWs in combination with the measured Stark shift of excitonic recombination is used to determine the polarization-induced electric fields in nanostructures. To facilitate inclusion of the predicted nonlinear polarization in future simulations, we give an explicit prescription to calculate polarization-induced electric fields and bound interface charges for arbitrary composition in each of the ternary III-N alloys. In addition, the theoretical and experimental results presented here allow a detailed comparison of the predicted electric fields and bound interface charges with the measured Stark shift and the sheet carrier concentration of polarization-induced 2DEGs. This comparison provides an insight into the reliability of the calculated nonlinear piezoelectric and spontaneous polarization of group III nitride ternary alloys.

Ab initio calculations of elastic constants and thermodynamic properties of bcc, fcc, and hcp Al crystals under pressure

Abstract: We have performed ab initio electronic structure and total-energy calculations for bcc, fcc, and hcp Al structures to study the equations of state, volume dependences of elastic constants, and relative stability diagram for these structures. A technique for elastic constant calculation in the case of initial isotropic pressure is presented. In this study we used the accurate full-potential linear muffin-tin orbital method to describe electrons of the crystal and the Debye treatment of the vibrating lattice. The volume dependence of the Debye temperature is derived from the volume dependence of the elastic constants. Our calculations show that at pressures of 1–2 Mbar and temperatures of about 1000 K and higher, the aluminium structure must have a lower symmetry than the structures considered.

The Verwey transition - a topical review

Abstract: This review encompasses the story of the Verwey transition in magnetite over a period of about 90 years, from its discovery up to the present. Despite this long period of thorough investigation, the intricate multi-particle system Fe3O4 with its various magneto-electronic interactions is not completely understood, as yet - although considerable progress has been achieved, especially during the last two decades. It therefore appeared appropriate to subdivide this retrospect into three eras: (I) from the detection of the effect to the Verwey model (1913-1947), being followed by a period of: (II) checking, questioning and modification of Verwey's original concepts (1947-1979). Owing to prevailing under-estimation of the role of crystal preparation and qualitiy control, this period is also characterized by a series of uncertainties and erroneous statements concerning the reaction order (one or two) and type of the transition (multi-stage or single stage). These latter problems, beyond others, could definitely be solved within era (III) (1979 to the present) - in favour of a first-order, single-stage transition near 125 K - on the basis of experimental and theoretical standards established in the course of a most inspiring conference organized in 1979 by Sir Nevill Mott in Cambridge and solely devoted to the present topic. Regarding the experimental field of further research, the remarkable efficiency of magnetic after-effect (MAE) spectroscopy as a sensitive probe for quality control and investigation of low-temperature (4 K Tv) into a Wigner crystal (T

Fundamental measure theory for hard-sphere mixtures revisited: the White Bear version

Abstract: We develop a density functional for hard-sphere mixtures which keeps the structure of Rosenfeld's fundamental measure theory (FMT) whilst inputting the Mansoori–Carnahan–Starling–Leland bulk equation of state. Density profiles for the pure hard-sphere fluid and for some binary mixtures adsorbed at a planar hard wall obtained from the present functional exhibit some improvement over those from the original FMT. The pair direct correlation function c(2) (r) of the pure hard-sphere fluid, obtained from functional differentiation, is also improved. When a tensor weight function is incorporated for the pure system our functional yields a good description of fluid–solid coexistence and of the properties of the solid phase.

Properties of GaN and related compounds studied by means of Raman scattering

Abstract: In the last decade, we have seen very rapid and significant developments in Raman scattering experiments on GaN and related nitride compounds: the Γ-point phonon frequencies have been identified for both cubic and hexagonal structures of binary compounds of GaN, AlN, and InN. The phonon spectra of their ternary alloys, InGaN and AlGaN, were also intensively studied. On the basis of these studies, characterizations of strain, compositional fluctuation, defects, impurities, etc, are now being intensively conducted. Besides such pure lattice properties, coupled modes between a lattice vibration (LO phonon) and a collective excitation of free carriers (plasmon) in GaN have been thoroughly studied, and the results are now widely applied to characterize carrier-transport properties. Low-dimensional structures of nitrides such as quantum dots and superlattices will soon enter the most active field of Raman scattering characterization. This article briefly reviews the present status of Raman scattering experiments on GaN and related nitride compounds and presents some future prospects.

Heterogeneous dynamics in liquids: fluctuations in space and time

Abstract: The disordered nature of glass-forming melts gives rise to non-Arrhenius and non-exponential behaviour of their dynamics. With respect to the microscopic details involved in the structural relaxation, these materials have remained an unsolved puzzle for over a century. The observation of spatial heterogeneity regarding the dynamics provides an important step towards understanding the relation between the macroscopic properties of soft condensed matter and the molecular mechanisms involved. On the other hand, dynamic heterogeneity is the source of several new questions: What is the length scale and persistence time associated with such clusters of relaxation time? What is the signature of heterogeneity at high temperatures and in the glassy state? How do these features depend on the particular material and on the correlation function used for probing these heterogeneities? This work attempts to review the various approaches to heterogeneous dynamics and the generally accepted results, as well as some controversial issues. Undoubtedly, heterogeneity has provoked a number of novel experimental techniques targeted at studying glass-forming liquids at the molecular level. It will be emphasized that the picture of heterogeneity is a requirement for rationalizing an increasing number of experimental observations rather than just an alternative model for the dynamics of molecules.

The standard Gaussian model for block copolymer melts

Abstract: As a result of important advances over the last decade, block copolymer melts have become an excellent model system for studying fundamental phenomena associated with molecular self-assembly. During this time, good quantitative agreement has been achieved between theory and experiment in regards to equilibrium phase behaviour, and with it has emerged a thorough understanding in terms of simple intuitive explanations. The theoretical contributions to this effort are largely attributed to mean-field calculations on a standard Gaussian model. Here, we review this present understanding of block copolymer phase behaviour, the model and its underlying assumptions, the mean-field approximation and its limitations, and the attempts to incorporate fluctuation corrections. Rather than following the traditional rigorous derivations, we present slightly more intuitive and transparent ones in such a way to stress the close connection between the related calculations. In this way, we hope to provide a valuable introduction to block copolymer theory.

Testing the limits of quantum mechanics: motivation, state of play, prospects

Abstract: I present the motivation for experiments which attempt to generate, and verify the existence of, quantum superpositions of two or more states which are by some reasonable criterion `macroscopically' distinct, and show that various a priori objections to this programme made in the literature are flawed. I review the extent to which such experiments currently exist in the areas of free-space molecular diffraction, magnetic biomolecules, quantum optics and Josephson devices, and sketch possible future lines of development of the programme.

Atomistic simulations of complex materials: ground-state and excited-state properties

Abstract: The present status of development of the density-functional-based tightbinding (DFTB) method is reviewed. As a two-centre approach to densityfunctional theory (DFT), it combines computational efficiency with reliability and transferability. Utilizing a minimal-basis representation of Kohn–Sham eigenstates and a superposition of optimized neutral-atom potentials and related charge densities for constructing the effective many-atom potential, all integrals are calculated within DFT. Self-consistency is included at the level of Mulliken charges rather than by self-consistently iterating electronic spin densities and effective potentials. Excited-state properties are accessible within the linear response approach to time-dependent (TD) DFT. The coupling of electronic and ionic degrees of freedom further allows us to follow the non-adiabatic structure evolution via coupled electron–ion molecular dynamics in energetic particle collisions and in the presence of ultrashort intense laser pulses. We either briefly outline or give references describing examples of applications to ground-state and excited-state properties. Addressing the scaling problems in size and time generally and for biomolecular systems in particular, we describe the implementation of the parallel ‘divide-and-conquer’ order-N method with DFTB and the coupling of the DFTB approach as a quantum method with molecular mechanics force fields.

The physics of a model colloid–polymer mixture

Abstract: The addition of non-adsorbing polymer to a colloidal suspension induces an interparticle 'depletion' attraction whose range and depth can be 'tuned' independently by altering the polymer's molecular weight and concentration respectively. Over the past decade, one particularly simple experimental realization of such a mixture has been studied in considerable detail: nearly-hard-sphere particles of poly(methyl methacrylate) and random-coil polystyrene dispersed in simple hydrocarbon solvents (mainly cis-decalin). The simplicity of the system has enabled rather detailed comparison of experimental findings with theory and simulation. Here I review the current understanding of the equilibrium phase behaviour, structure, phase transition kinetics, and metastability of this model colloid–polymer mixture. These findings form a useful reference point for understanding more complex mixtures. Moreover, in some cases, insights gained from studying this model system have relevance beyond soft-condensed-matter physics, e.g. in understanding the liquid state, in controlling protein crystallization, and in elucidating the nature of glasses.

Nanostructuring surfaces by ion sputtering

Abstract: Surface etching by ion sputtering can be used to pattern surfaces. Recent studies using the high-spatial-resolution capability of the scanning tunnelling microscope revealed in fact that ion bombardment produces repetitive structures at nanometre scale, creating peculiar surface morphologies ranging from self-affine patterns to `fingerprint'-like and even regular structures, for instance waves (ripples), chequerboards or pyramids. The phenomenon is related to the interplay between ion erosion and diffusion of adatoms (vacancies), which induces surface re-organization. The paper reviews the use of sputter etching to modify `in situ' surfaces and thin films, producing substrates with well defined vertical roughness, lateral periodicity and controlled step size and orientation.

Coupling Poisson–Nernst–Planck and density functional theory to calculate ion flux

Abstract: Ion transport between two baths of fixed ionic concentrations and applied electrostatic (ES) potential is analysed using a one-dimensional drift-diffusion (Poisson–Nernst–Planck, PNP) transport system designed to model biological ion channels. The ions are described as charged, hard spheres with excess chemical potentials computed from equilibrium density functional theory (DFT). The method of Rosenfeld (Rosenfeld Y 1993 J. Chem. Phys. 98 8126) is generalized to calculate the ES excess chemical potential in channels. A numerical algorithm for solving the set of integral–differential PNP/DFT equations is described and used to calculate flux through a calcium-selective ion channel.

Photonic band-gap effects and magnetic activity in dielectric composites

Abstract: We develop an effective medium description of a two-dimensional photonic band-gap medium composed of dielectric cylinders of large dielectric constant. Using the transfer matrix method we have calculated reflection coefficients for a slab of the composite and plane-wave incidence, as well as the (complex) wavevector for the infinite system. From these quantities we derive an effective permittivity and permeability for the composite. In the case of p-polarized incidence the composite displays a negative magnetic permeability at microwave frequencies due to single-scatterer resonances in the medium.

Electrical conductivity and dielectric behaviour of nanocrystalline NiFe2O4 spinel

Abstract: Electrical conductivity and dielectric measurements have been performed for nanocrystalline NiFe2O4 spinel for four different average grain sizes, ranging from 8 to 97 nm. The activation energy for the grain and grain boundary conduction and its variation with grain size have been reported in this paper. The conduction mechanism is found to be due to the hopping of both electrons and holes. The high-temperature conductivity shows a change of slope at about 500 K for grain sizes of 8 and 12 nm and this is attributed to the hole hopping in tetrahedral sites of NiFe2O4. Since the activation energy for the dielectric relaxation is found to be almost equal to that of the dc conductivity, the mechanism of electrical conduction must be the same as that of the dielectric polarization. The real part e' of the dielectric constant and the dielectric loss tanδ for the 8 and 12 nm grain size samples are about two orders of magnitude smaller than those of the bulk NiFe2O4. The anomalous frequency dependence of e' has been explained on the basis of hopping of both electrons and holes. The electrical modulus analysis shows the non-Debye nature of the nanocrystalline nickel ferrite.

Recent experimental studies of electron dephasing in metal and semiconductor mesoscopic structures

Abstract: In this review, we discuss the results of recent experimental studies of the low-temperature electron dephasing time (τφ) in metal and semiconductor mesoscopic structures. A major focus of this review is on the use of weak localization, and other quantum-interference-related phenomena, to determine the value of τφ in systems of different dimensionality and with different levels of disorder. Significant attention is devoted to a discussion of three-dimensional metal films, in which dephasing is found to predominantly arise from the influence of electron–phonon (e–ph) scattering. Both the temperature and electron mean free path dependences of τφ that result from this scattering mechanism are found to be sensitive to the microscopic quality and degree of disorder in the sample. The results of these studies are compared with the predictions of recent theories for the e–ph interaction. We conclude that, in spite of progress in the theory for this scattering mechanism, our understanding of the e–ph interaction remains incomplete. We also discuss the origins of decoherence in low-diffusivity metal films, close to the metal–insulator transition, in which evidence for a crossover of the inelastic scattering, from e–ph to ‘critical’ electron–electron (e–e) scattering, is observed. Electron– electron scattering is also found to be the dominant source of dephasing in experimental studies of semiconductor quantum wires, in which the effects of both large- and small-energy-transfer scattering must be taken into account. The latter, Nyquist, mechanism is the stronger effect at a few kelvins, and may be viewed as arising from fluctuations in the electromagnetic background, generated by the thermal motion of electrons. At higher temperatures, however, a crossover to inelastic e–e scattering typically occurs; and evidence for this large-energy-transfer process has been found at temperatures as high as 30 K. Electron–electron interactions are also thought to play an important role in dephasing in ballistic quantum dots, and the results of recent experiments in this area are reviewed. A common feature of experiments, in both dirty metals 3 Authors to whom any correspondence should be addressed.

Beware of density dependent pair potentials

Abstract: Density (or state) dependent pair potentials arise naturally from coarse-graining procedures in many areas of condensed matter science. However, correctly using them to calculate physical properties of interest is subtle and cannot be uncoupled from the route by which they were derived. Furthermore, there is usually no unique way to coarse-grain to an effective pair potential. Even for simple systems like liquid argon, the pair potential that correctly reproduces the pair structure will not generate the right virial pressure. Ignoring these issues in naive applications of density dependent pair potentials can lead to an apparent dependence of thermodynamic properties on the ensemble within which they are calculated, as well as other inconsistencies. These concepts are illustrated by several pedagogical examples, including effective pair potentials for systems with many-body interactions, and the mapping of charged (Debye–Huckel) and uncharged (Asakura–Oosawa) two-component systems onto effective one-component ones. The differences between the problems of transferability and representability for effective potentials are also discussed.

The crystal structure and phase transitions of the magnetic shape memory compound Ni2MnGa

Abstract: High resolution neutron powder diffraction and single crystal measurements on the ferromagnetic shape memory compound Ni2MnGa have been carried out. They enabled the sequence of transformations which take place when the unstressed, stoichiometric compound is cooled from 400 to 20 K to be established. For the first time the crystallographic structure of each of the phases which occur has been determined. At 400 K the compound has the cubic L21 structure, and orders ferromagnetically at TC ≈ 365 K. On cooling below ~ 260 K a super-structure, characterized by tripling of the repeat in one of the 110cubic directions, forms. This phase, known as the pre-martensitic phase, persists down to the structural phase transition at TM ≈ 200 K and can be described by an orthorhombic unit cell with lattice parameters aortho = 1/√2acubic, bortho = 3/√2acubic, cortho = acubic and space group Pnnm. Below TM the compound has a related orthorhombic super-cell with bortho ≈ 7/√2acubic, which can be described within the same space group. The new modulation appears abruptly at TM and remains stable down to at least 20 K.

Ab initio molecular dynamics: basic concepts, current trends and novel applications

Abstract: The field of ab initio molecular dynamics (AIMD), in which finite temperature molecular dynamics (MD) trajectories are generated with forces obtained from accurate 'on the fly' electronic structure calculations, is a rapidly evolving and growing technology that allows chemical processes in condensed phases to be studied in an accurate and unbiased way. This article is intended to present the basics of the AIMD method as well as to provide a broad survey of the state of the art of the field and showcase some of its capabilities. Beginning with a derivation of the method from the Born–Oppenheimer approximation, issues including the density functional representation of electronic structure, basis sets, calculation of observables and the Car–Parrinello extended Lagrangian algorithm are discussed. A number of example applications, including liquid structure and dynamics and aqueous proton transport, are presented in order to highlight some of the current capabilities of the approach. Finally, advanced topics such as inclusion of nuclear quantum effects, excited states and scaling issues are addressed.

Conjugated polymer blends: linking film morphology to performance of light emitting diodes and photodiodes

Abstract: Blending is a technique known in polymer technology that takes advantage of the processibility of polymers to produce new solid materials or composites with specific structural and physical properties, distinct from the ones of their components. In thin films of polymer blends interesting morphologies are formed because of phase separation. For conjugated polymers, i.e. solution-processible semiconductors, blending also opens a way to optimize the performance of opto-electronic devices, bringing about technological benefits. It is therefore crucial to achieve understanding of the effect film morphology has on the device performance, and, ultimately, to achieve control over the phase separation in a blend, so that structures can be designed that yield the desired device performance. Light-emitting diodes (LEDs) made of polymer blends have shown strongly enhanced electroluminescence (EL) efficiencies, as compared to pure homopolymers. Colour conversion, white light emission, polarized light emission, emission line narrowing, and voltage-tunable colours are other effects that have been observed in blends containing light-emitting polymers. Although the enhanced EL efficiency is attributed to F?rster-type energy transfer in numerous reports, the exciton dynamics behind this effect is not well understood. Here we review the formation and morphology of thin films of conjugated polymer blends, as well as modern microscopic and spectroscopic techniques to study them. Furthermore, we attempt to link the film morphology to the electronic performance of electroluminescent and photovoltaic devices and discuss energy and charge transfer phenomena at the interfaces. We also report some new results, specifically for polyfluorene blends in LEDs. This article was originally intended for publication in Issue 42 of this volume, which was a special issue on Conjugated Polymers: Issue 42

Specific heat of MgB2 in a one- and a two-band model from first-principles calculations

Abstract: The heat capacity anomaly at the transition to superconductivity of the layered superconductor MgB2 is compared to first-principles calculations with the Coulomb repulsion, µ*, as the only parameter which is fixed to give the measured Tc. We solve the Eliashberg equations for both an isotropic one-band model and a two-band model with different superconducting gaps on the π-band and σ-band Fermi surfaces. The agreement with experiments is considerably better for the two-band model than for the one-band model.

Spectroscopic probing of local hydrogen-bonding structures in liquid water

Abstract: We have studied the electronic structure of liquid water using x-ray absorption spectroscopy at the oxygen K edge. Since the x-ray absorption process takes less than a femtosecond, it allows probing of the molecular orbital structure of frozen, local geometries of water molecules at a timescale that has not previously been accessible. Our results indicate that the electronic structure of liquid water is significantly different from that of the solid and gaseous forms, resulting in a pronounced pre-edge feature below the main absorption edge in the spectrum. Theoretical calculations of these spectra suggest that this feature originates from specific configurations of water, for which the H-bond is broken on the H-donating site of the water molecule. This study provides a fingerprint for identifying broken donating H-bonds in the liquid and shows that an unsaturated H-bonding environment exists for a dominating fraction of the water molecules.

Magnetic activity at infrared frequencies in structured metallic photonic crystals

Abstract: We derive the effective permeability and permittivity of a nanostructured metallic photonic crystal by analysing the complex reflection and transmission coefficients for slabs of various thicknesses. These quantities were calculated using the transfer matrix method. Our results indicate that these structures could be used to realize a negative effective permeability, at least up to infrared frequencies. The origin of the negative permeability is a resonance due to the internal inductance and capacitance of the structure. We also present an analytic model for the effective permeability of the crystal. The model reveals the importance of the inertial inductance due to the finite mass of the electrons in the metal. We find that this contribution to the inductance has implications for the design of metallic magnetic structures in the optical region of the spectrum. We show that the magnetic activity in the structure is accompanied by the concentration of the incident field energy into very small volumes within the structure. This property will allow us to considerably enhance non-linear effects with minute quantities of material.

Surface properties of the half-and full-Heusler alloys

Abstract: Using a full-potential ab initio technique I study the electronic and magnetic properties of the (001) surfaces of the half-Heusler alloys NiMnSb, CoMnSb and PtMnSb and of the full-Heusler alloys Co2MnGe, Co2MnSi and Co2CrAl. The MnSb-terminated surfaces of the half-Heusler compounds present properties similar to those of the bulk compounds and, although the half-metallicity is lost, an important spin polarization at the Fermi level. In contrast to this, the Ni-terminated surface shows an almost zero net spin polarization. While the bulk Co2MnGe and Co2MnSi are almost half-ferromagnetic, their surfaces lose the half-metallic character and the net spin polarization at the Fermi level is close to zero. In contrast, the CrAl-terminated (001) surface of Co2CrAl shows a spin polarization of about 84%.

Dense astrophysical plasmas

Abstract: We briefly examine the properties of dense plasmas characteristic of the atmospheres of neutron stars and of the interior of massive white dwarfs. These astrophysical bodies are natural laboratories for studying respectively the problem of pressure ionization of hydrogen in a strong magnetic field and the crystallization of the quantum one-component plasma at finite temperature.

Conceptual improvements of the KKR method

Abstract: We review some recent conceptual improvements of the Korringa–Kohn–Rostoker (KKR) Green function method for electronic structure calculations. After an introduction into the KKR–Green function method we present an extension of this method into an accurate full-potential scheme, which allows calculation of forces and lattice relaxations. The additional numerical effort compared to the atomic sphere approximation scales only linear with the number of atoms. In addition, we discuss the recently developed screened KKR method which represents a reformulation of the multiple scattering theory with exponentially decreasing structure constants. This method, which has the same accuracy as the standard KKR method, exhibits strong advantages for two-dimensional systems like multilayers or surfaces, since the numerical effort scales linearly with the number of layers. The strength of both methods is illustrated in typical applications.