Electronic Structure Calculations Using WIEN97: Fermi Surface of Metals and Alloys

               

Principal Investigator

Robert Leckey

School of Physics,

Faculty of Science and Technology,

La Trobe University

The topology of the Fermi surface of metals and alloys is of critical importance in that it is fundamental to the electronic and magnetic properties of the materials. Recently, angle-resolved ultraviolet photoelectron spectroscopy has been shown to provide very direct information on the Fermi surface of two-dimensional systems. For truly three-dimensional systems the situation is somewhat more complicated, and the experimental data must be combined with calculations in order to obtain accurate Fermi surface dimensions. As this technique, however, is still in its infancy, it is necessary to study systems with relatively simple and well defined Fermi surfaces and to compare the experimental results to state-of-the-art calculations. WIEN97 is a full-potential linearised augmented plane wave package for electronic structure calculations in solids which we have started using for the purpose outlined above. The initial and final state electronic band structures of metals and semiconductors will be calculated and compared to experimental results.    

Co-Investigators

     

John Riley

Anton Stampfl

Roman Fasel

School of Physics,

Faculty of Science and Technology,

La Trobe University

     

Projects

g96 - PC

     
             

     
               

What are the results to date and the future of this work?

As reflected in the few SU used during the last period, we have not yet been able to fully exploit the WIEN97 package. By now, however, many problems related to the usage of the package have been solved and the first bulk bandstructures have been calculated (Fig. 1). A first Fermi surface calculation has been performed for magnesium (Fig. 2). In order to check for proper convergence these calculations will have to be repeated using larger parameters. Furthermore, the calculations will be extended to the surface of the materials under investigation, which will require a large amount of CPU time.

What computational techniques are used?

WIEN97 is a full-potential linearized augmented plane wave (FLAPW) package, which does not make any approximations on the shape of the potential, which is calculated self-consistently. Therefore, the FLAPW method is among the most accurate methods for performing electronic structure calculations for crystals. Accordingly, calculations are computationally intensive, particularly when surfaces are taken into account. Furthermore, the size of the WIEN97 calculations requires a powerful workstation with 256 Mb or more of memory and 1-4 Gb of disk space. In its present version, the WIEN97 code includes k-point parallelization and special routines for the SGI R10000 processor.

               
- Appendix B

 
               

             
Figure 1. Calculated bandstructure of hcp magnesium along the main directions of the Brillouin zone. The calculation has been performed using the full-potential linear augmented plane-wave method (FLAPW) as implemented in the program-package.
             

a) ARUPS Experiment

b) FLAPW Calculation

             
a) Experimental Fermi surface map from Mg(0001). This map represents the intensity of the photoelectrons emitted from the Fermi edge as a function of emission angle and thus as a function of parallel momentum. The intensities are given in a linear grey scale with low intensity corresponding to white and high intensity to black. b) Corresponding calculated Fermi surface map, assuming a free-electron final-state. The calculation has been performed using the full-potental linear augmented plane-wave method (FLAPW) as implemented in the program-package WIEN97
       
             
Appendix B -