Generalized Kohn-Sham (GKS) HOMO and LUMO orbital energies have been rigorously established to be the chemical potentials of electron removal and addition, making them good approximations to negative ionization potential (IP) and electron affinity (EA) from a density functional approximation (DFA) with minimal delocalization error. For other quasiparticle energies (higher IPs and lower EAs), their connection to the GKS orbital energies has not been established but remains highly interesting. In this work, we provide the comparison of experimental quasiparticle energies for many finite systems with calculations from the GW Green's function and localized orbitals scaling correction (LOSC), a recently developed correction to semilocal DFAs, which has minimal delocalization error. Numerical results in this work 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 calculations of excitation energies of the <i>N</i>-electron systems from the ground state DFA calculations of the (<i>N-1</i>) -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 Rydberg states, good accuracy was obtained only with the use of LOSC DFA. This work highlights the pathway to quasiparticle and excitation energies from ground density functional calculations.

Approximating quasiparticle and excitation energies from ground state generalized Kohn–Sham calculations

2019 Fall National Meeting

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