Speaker：Prof. Steven G. Louie (University of California at Berkeley, and Lawrence Berkeley National Lab, Berkeley, California U.S.A.)
Time：2023/02/02 (Thur.) 14:00
Place：R307 Lecture Hall, Cosmology Hall NTU (Hybrid, Webex)

Online Link：https://nationaltaiwanuniversity-zbh.my.webex.com/nationaltaiwanuniversity-zbh.my/j.php?MTID=md14e7bffbb00eea4171d71c7eab0e966
Meeting number: 2552 973 1960
Password: YEy5cwfdh43 (93952933 from phones and video systems)

Abstract：
Accurate treatment of many-electron interactions is central to the understanding of many
phenomena in materials. We present some recent progress along this direction in investigating
from ab initio the electronic, transport and optical properties of a number of materials of current
interest, including atomically thin two-dimensional (2D) materials as well as 2D moiré
heterobilayers. Different measurements and phenomena entail different levels of theoretical
treatments. Photoemission and tunneling spectroscopies may be understood from the perspective
of an interacting 1-particle Green’s function. However, correlated multi-particle excitations such
as excitons, trions, and bi-excitons require knowledge of the 2-, 3- and 4-particle Green’s
functions, respectively. Nonequilibrium and time-dependent phenomena, such as those in field-
driven systems and pump-probe experiments, require yet different treatments from those of
equilibrium case. We discuss the concepts and methods behind the ab initio studies of these
phenomena, and give some examples including multi-particle excitations, linear and nonlinear
optical responses, transient optics, as well as field-driven time-resolved angle-resolved
photoemission spectroscopy (tr-ARPES). Moreover, we show that self-energy effects can play a
critical role in the electron-phonon coupling going beyond DFT, leading to transformative
understanding of properties such as superconductivity in some materials.