Leeor Kronik

Professor Leeor Kronik, Weizmann Institute of Science.  "Theoretical spectroscopy using density functional theory:  New ideas for long-standing problems."  Greater Boston Theoretical Chemistry Lecture.

Abstract

Accurate prediction of the electronic structure and optical properties is essential for rational design of materials for novel (opto)electronic applications. Quantities of interest include, e.g., the bandgap, band dispersion and band width, optical absorption, exciton binding energies, and more. Preferably, we would like to predict such quantities using density functional theory (DFT), because the relative computational simplicity afforded by DFT allows us to attack realistic problems. Unfortunately, despite many other successes, DFT has traditionally struggled with prediction of the above quantities. Specifically, research has been fraught with very difficult questions as to the extent to which spectroscopic conclusions can be drawn from DFT even in principle, followed by serious concerns as to the reliability of typical DFT approximations in practice. In this lecture, I will start with a tutorial overview on DFT. I will then focus on new formal and practical approaches which offer fresh answers to the above long-standing questions. In particular, I will show that DFT can, in many cases, mimic successfully the quasi-particle picture of many-body theory, allowing for quantitative calculations of both single- and two-particle excitations. I will show how this is achieved for finite systems, present initial generalizations to solids, and discuss limitations and remaining challenges.