VIRTUAL

 

Thursday, April 1st    2021

3:45 – 4:45 p.m.

WEBEX

 

Speaker:  Prof. Weitao Yang

Philip Handler Distinguished Professor of Chemistry

Department of Chemistry and Department  of Physics

Duke University, USA

 

 

“Photoemission and Photoexcitation Spectroscopy from Ground State DFT Calculations”

 

 

 

Abstract: 

The perspectives of fractional charges and fractional spins provide a clear analysis of the errors of commonly used density functional approximations (DFAs).  These errors, the delocalization and static correlation error, lead to diversified problems in present-day density functional theory calculations. For achieving a universal elimination of these two errors, we developed a localized orbital scaling correction (LOSC): it accurately characterizes the distributions of global and local fractional electrons and spins, and is thus capable of correcting system energy, energy derivative and electron density in a size-consistent manner. Our approach introduces the explicit derivative discontinuity and largely restores the flat-plane behavior of electronic energy at fractional charges and fractional spins. The LOSC–DFAs lead to systematically improved results, including the dissociation of ionic species, single bonds, multiple bonds without breaking the space or spin symmetry, the band gaps of molecules and polymer chains, the energy and density changes upon electron addition and removal, and photoemission spectra, and energy-level alignments for interfaces.

We carried the comparison of experimental quasiparticle energies for many finite systems with calculations from the GW Green function and LOSC.  Extensive results with over 40 systems clearly show that LOSC orbital energies achieve slightly better accuracy than the GW calculations with little dependence on the semilocal DFA, supporting the use of LOSC DFA orbital energies to predict quasiparticle energies. This also leads to the QE-DFT (quasiparticle energies from DFT) approach: the calculations of excitation energies of the N-electron systems from the ground state DFA calculations of the (N - 1)-electron systems. Results show good performance with accuracy similar to TDDFT and the delta SCF approach for valence excitations with commonly used DFAs with or without LOSC. For charge transfer and Rydberg states, good accuracy was obtained only with the use of LOSC DFA.  The QE-DFT method has been further developed to describe excited-state potential energy surfaces (PESs), conical intersections, and the analytical gradients of excited-state PESs.

 

Bio:

https://scholars.duke.edu/person/weitao.yang