Abstract:

Quantitative understanding of electronic excitations in semiconductors has been and still is a central topic of condensed matter theory because of its fundamental and technological importance. With the advent of modern electronic structure method that includes electron-electron and electron-hole interactions from first principles, theory is now used to predict and accurately compare with experiment excited-state properties of semiconductors and insulators without any adjusting parameters. 

However, there are some perceived exceptions. One widely discussed case is zinc oxide. In this talk, I will show, contrary to previous reports, that the conventional GW approximation is able to calculate accurately the experimental band gap (~ 3.6 eV) of ZnO. The widely discussed, severe underestimate of the quasiparticle gap of ZnO within the GW method is a result of an inadequate treatment of the semicore electrons and the slow and nonuniform convergence in the Coulomb-hole self-energy in previous calculations. In addition, an assumed small kinetic energy cut-off for the dielectric matrix may result in a false convergence behavior for the quasiparticle self-energy.

Profile:

       Prof. Zhang got his bachelor’s degree in Physics from Xiamen University in 1993, Master’s degree in Atomic & Molecular Physics from CAS in 1996 and Ph.D. degree in Condensed Matter Physics from Pennsylvania State University in 2001. He worked as a research scientist at Corning Incorporated during 2001 and 2003 and then went to Berkeley to do postdoctoral research with S.G. Louie and M.L. Cohen. Currently he has been an assistant professor at the University at Buffalo, SUNY since 2005. Up to now, he has numbers of papers published on best journals like Nature (1) and Physical Review Letters (10), cited by more than 750 times.