J. M. MacLaren

Layer Korringa-Kohn-Rostoker electronic structure code for bulk and interface geometries

Abstract A program is presented which implements the layer Koringer-Kohn-Rostoker theory for the electronic structure of both bulk systems and those characterised by two-dimensional periodicity. The one-electron Green function is obtained by recursively assembling the layers of the system, permitting the study of interface regions embedded in otherwise perfect host materials. The program enables the calculation of self-consistent charge densities and localised states.

The calculation of stacking fault energies in close-packed metals

The one-electron theory of metals is applied to the calculation of stacking fault energies in face-centered cubic metals. The extreme difficulties in calculating fault energies of the order of 0.01 eV/(interface unit-cell area) are overcome by applying the Force theorem and using the layer--Korringer--Kohn--Rostoker method to determine the charge density of isolated defects. A simple scheme is presented for accommodating deviations from charge neutrality inherent in this approach. The agreement between theoretical and experimental values for the stacking fault energy is generally good, with contributions localized to within three atomic planes of the fault, but suggest the quoted value for Rh is a significant over-estimation.

Magnetic and electronic properties of Au/Fe superlattices and interfaces

The electronic and magnetic structure of AunFe(100) superlattices and interfaces are investigated with the layer Korringa–Kohn–Rostoker technique. Enhanced magnetism, over that of bulk bcc Fe, is observed on the Fe layer in all geometries studies. In the supercell geometry the magnetic moment decreases as the number of mediating Au layers is increased, reaching the same asymptotic value as obtained in the interface calculation. These results can be understood in terms of very weak Fe‐Au coupling in these systems. The Fe minority‐hole states are mainly d states with character orthogonal to the Fe plane, suggesting a tendency for out‐of‐plane (perpendicular) magnetic anisotropy.

Electronic and magnetic properties of Fe/Au multilayers and interfaces

Abstract The electronic and magnetic structure of Fe/Au superlattices and interfaces are investigated with the, recently developed, layer Korringa-Kohn-Rostoker method. Enhanced magnetism is seen in the Fe layer in all supercell and interface geometries studied with weak coupling between the Fe and Au layers. The Fe moment decreases gradually from 2.78 to 2.74μ B as the number of mediating Au planes increases, converging to that obtained in the interface calculations. The Fe minority-hole states consist mainly of d-states with character orthogonal to the Fe plane which, if analysed in terms of a vector model for the orbital moment, would suggest a tendency for out-of-plane (perpendicular) anisotropy. Localized states, in gaps in the two-dimensional (2-D) band structure, were found at the X-point of the 2-D Brillouin Zone. These states are strongly localized, both in energy and space.

Quantum mechanics and mechanical properties: towards twenty-first century materials

Abstract The use of materials with otherwise attractive properties is often limited by unacceptable mechanical performance. Fortunately, modern processing techniques are sometimes able to overcome such deficiencies, though a systematic and fundamental approach to materials development has yet to be devised. Recent advances in quantum-mechanical computational capabilities have fostered a growing number of applications that bear directly upon the mechanical properties of materials. After a brief discussion of the role of defect structures in mediating deformation behaviour, techniques for computing properties of solids within a quantum-mechanical framework are reviewed. Examples are cited where insight into macroscopic behaviour has been attained from the application of quantum-mechanical calculations to materials of technological importance.

Parameterised local spin density exchange-correlation energies and potentials for electronic structure calculations. I, Zero temperature formalism

Commonly used approximate forms for the exchange-correlation energy and potential within the local density approximation are summarised, and FORTRAN code is included for the evaluation of these various forms. Included are the following: Xα, Kohn-Sham-Gaspar, Hedin-Lundqvist-Wilkins, Janak-Moruzzi-Williams, Von Barth-Hedin, Ceperley-Alder (Perdew-Zunger), and Ceperley-Alder (Vosko-Wilk-Nusair). Both the Vosko-Wilk-Nusair and the Von Barth-Hedin expressions for spin interpolation between paramagnetic and ferromagnetic limits are also provided.

Magnetic structure of {111} stacking faults in nickel

The magnetic structure of {111} stacking faults in nickel is investigated utilizing a fully self‐consistent, layered Korringa–Kohn–Rostoker approach which does not require full three‐dimensional symmetry or the use of finite‐sized slabs. Localized electronic states appear at the faults. The spin polarization is calculated for a twin boundary, an intrinsic fault, an extrinsic fault, and several other stacking sequences. In all cases, the magnetic moment is found to be insensitive to the orientation of the nearest‐neighbor atoms, but instead can be related to the distance to the nearest atom in the direction perpendicular to the fault plane. Very simple empirical expressions for calculating the spin polarization and total energy of any stacking configuration are presented.

Interface electronic structure of XDTM titanium aluminide composites

Abstract The electronic structure of TiAl, TiB 2 , TiAlue5f8TiB 2 interfaces are studied with the layer Korringa-Kohn-Rostoker method. These interfaces occur in titanium aluminide composites produced by a casting process known as XD TM technology, which allows engineering of the microstructure to achieve specified properties. By examining and comparing the bonding in TiAl and TiB 2 , the calculations suggest that the bonding between the titanium and the boron at the interface is inhibited by the presence of aluminum. The implications of these results are then explored for other alloying additions at the interface, and for the interaction between the chemistry at the interface and mechanical behavior of these materials.