Helmut Bross (physicist)

Helmut Bross, 2012

Helmut Bross (born May 23, 1931 in Mühlacker ) is a German theoretical physicist who made important contributions to the theory and calculation of the electronic structure of solids .

Life

Helmut Bross grew up in his hometown Mühlacker and attended schools there. From 1949 to 1955 he studied physics at the Technical University of Stuttgart . He completed his diploma, doctoral and post-doctoral theses with Ulrich Dehlinger and his then assistant Alfred Seeger at the Institute for Theoretical and Applied Physics (ITAP) at the Technical University of Stuttgart. In his diploma thesis and his doctoral thesis, Bross devoted himself to questions of the electrical conductivity of metals . In his habilitation thesis he dealt with a question of the thermal conductivity of solids .

At the beginning of the 1960s, Bross turned to the question of a numerical calculation of the electronic band structure of crystals that was as precise as possible . For this, the basic equation of quantum mechanics , the so-called Schrödinger equation with the periodic boundary conditions for the electrons in a crystal, has to be solved. The usual procedure for all band structure calculations is to replace the electron many-particle system with a one-electron system in which the electron- electron interaction is approximated by a one-particle potential . In solid-state physics, the approximation of density functional theory is generally used. The Fourier transformation is often used to solve linear partial differential equations with periodic boundary conditions, such as the electron-Schrödinger equation in the crystal , which results in a linear system of equations . Near the atomic nuclei converge , however, the plane waves of the Fourier transform is not good enough, one that in this area the crystal electron - wave functions by spherical harmonics and radial solutions of the Schrödinger equation in the strong nucleus potential approximated.

Bross achieved a breakthrough in these high-precision band structure calculations by further developing Slater's Augmented Plane Wave Method ( APW ) into the Modified Augmented Plane Wave Method ( MAPW ). Here, the partial differential equation is first converted into a mathematically equivalent variation problem, which then delivers a linear system of equations with the help of a Rayleigh-Ritz method . This can be solved using standard numerical mathematics methods on high-performance computers . MAPW has two major advantages over other methods: on the one hand, it provides linear systems of equations and, on the other hand, it ensures that the calculated crystal electron wave functions are continuously differentiable everywhere . The continuity properties of the MAPW wave functions enable both good convergence of the electron energies and physically correct wave functions. From these results one can then calculate all interesting electronic crystal properties by suitable differentiations and integrations . Bross was able to decisively improve the differentiations of the crystal electron wave functions through a skillful application of the Hellmann-Feynman theorem and the integrations through the introduction of magic points .

In 1965, Bross was appointed to a newly created chair for theoretical solid-state physics at the Ludwig Maximilians University in Munich , where he studied the electronic structure and physical properties together with his long-time assistants and many doctoral and diploma students and the excellent possibilities of the Leibniz data center many crystals could calculate. A generalization of the procedure to the case of the relativistic Dirac equation , the Relativistic Modified Augmented Plane Wave Method , RMAPW , was developed in 1969 by Bross and Hofmann, and in 1984 by Schiekel at the Bross chair.

Helmut Bross trained two generations of theoretical solid-state physicists, a number of whom are now professors at various universities. In addition, he spent numerous research semesters at research institutions and foreign universities, including at the IBM Research Center Yorktown Heights and several times at Montana State University in Bozeman .

Even after his retirement in 1999, Bross continued his research in the Theoretical Solid State Physics working group at the Ludwig Maximilians University in Munich. His current topic (2010) is the electronic structure of graphs .

Web links

• Helmut Bross on the website of the University of Munich
• ITAP Stuttgart website
• Website of the Theoretical Solid State Physics Group at LMU Munich

Individual evidence

1. ↑ Helmut Bross: Association energy and the increase in electrical resistance in monovalent metals , University of Stuttgart, 1955.
2. ↑ Helmut Bross: The electrical conductivity of copper with special consideration of the anisotropy of the lattice vibration spectrum , University of Stuttgart, 1959.
3. ↑ Helmut Bross: The influence of imperfections on the lattice thermal conductivity at low temperatures , University of Stuttgart, 1962.
4. ^ JC Slater: Wave Function in a Periodic Potential , Phys. Rev. 51, p. 846, 1937.
5. ↑ Terry Loucks: Augmented Plane Wave Method , WA Benjamin Inc., New York 1967.
6. ↑ H. Bross, Phys. condes. Materie 3, pp. 119-138 (1964).
7. ↑ H. Bross, G. Bohn, G. Meister, W. Schubö, H. Stöhr: Phys. Rev. B 2, p. 3098, 1970
8. ↑ H. Bross, J. Phys. B 28, p. 2631, 1978
9. ^ H. Bross, I. Hofmann: Z. Physik, 229, p. 123, 1969.
10. ↑ Bernhard Schiekel: RMAPW process and self-consistent band structure of gold , Dissertation, University of Munich. 1984
11. ↑ Lecture at TUM on the electronic structure of graphs