Elisabeth Sjöstedt

An alternative way of linearizing the augmented plane-wave method

A new basis set for a full potential treatment of crystal electronic structures is presented and compared to that of the well-known linearized augmented plane-wave (LAPW) method. The basis set consists of energy-independent augmented plane-wave functions combined with local orbitals. Each basis function is continuous over the whole unit cell but it may have a discontinuous slope at the muffin-tin boundaries, i.e. at the surfaces of atomic centered, non-overlapping spheres. This alternative way to linearize the augmented plane-wave method is shown to reproduce the accurate results of the LAPW method, but using a smaller basis set size. The reduction in number of basis functions is most significant for open structures.

Detailed study of the magnetic circuit in a longitudinal flux permanent-magnet synchronous linear generator

We present the results of a theoretical study of the magnetic circuit of a longitudinal flux permanent-magnet synchronous linear generator. In our study, we used a coupled field and circuit model solved by a time-stepping finite-element technique to analyze the machine. We investigated the effects of different permanent-magnet shapes and sizes, as well as different stator steel geometries. We noted a significant difference in performance for different magnet shapes. Our results also illustrate how small changes, on a millimeter scale, will affect the flux path, and thereby the overall performance of the machine, highlighting the importance of stator steel geometry.

Converting kinetic energy in small watercourses using direct drive generators

Tidal currents, ocean currents and unregulated watercourses are all large sources of energy that can be converted into electricity. Several technical and economical solutions within this research area have been demonstrated. In literature there exists two different turbine types, horizontal and vertical axis. The present paper focuses on the design of a permanent magnetized generator directly coupled to a vertical axis turbine. The proposed theoretical concept is adapted to data measurements regarding water current velocities and flow profiles from a Swedish watercourse. A high electromagnetic efficiency of 90% is obtained.Copyright

Hyperfine Parameters of η′-Cu6Sn5 and Li2CuSn

Abstractη′-Cu6Sn5, a suggested anode material in Li-ion batteries, has been studied by 119Sn Mössbauer spectroscopy together with the lithiated phase Li2CuSn. Full-potential electronic structure calculations were carried out using full potential LAPW (linearized augmented plane wave) within the local density approximation. The calculated hyperfine parameters, isomer shift and electric quadrupole splitting, were compared to the experimental. In presence of more than one Sn-site, the theoretical values provide a good starting guess to fit a single Mössbauer absorption peak to different sites.

Efficient solution of the non-linear augmented plane wave secular equation

A new way of solving the non-linear secular equation within the augmented plane wave (APW) method is presented. The traditional computation of the APW secular determinant is replaced by a scheme where we follow the eigenvalues of the secular matrix for a number of energies. These eigenvalues, referred to as the meta-eigenvalues of the original APW problem, provide more information about the system for each energy examined than just their product, i.e. the value of the secular determinant. The new scheme for finding the APW eigenvalues can be made considerably more efficient than the traditional one, and is useful in calculations where a linearized approximation to the APW secular matrix is insufficient, such as for optical calculations extending over a wide energy range or for energy dependent effective potentials.