Approximating Quasiparticle and Excitation Energies from Ground State Generalized Kohn-Sham Calculations

TL;DR

This paper demonstrates that LOSC-corrected orbital energies from ground state DFT can accurately approximate quasiparticle and excitation energies, offering a practical alternative to more complex methods like GW and TDDFT.

Contribution

It establishes the effectiveness of LOSC-corrected orbital energies in predicting quasiparticle and excitation energies from ground state calculations, with minimal dependence on the underlying DFA.

Findings

LOSC orbital energies outperform some GW calculations in accuracy.

LOSC DFA orbital energies reliably predict quasiparticle energies.

Good accuracy for valence and Rydberg excitations, especially with LOSC correction.

Abstract

Quasiparticle energies and fundamental band gaps in particular are critical properties of molecules and materials. It was rigorously established that the generalized Kohn-Sham HOMO and LUMO orbital energies are the chemical potentials of electron removal and addition and thus good approximations to band edges and fundamental gaps from a density functional approximation (DFA) with minimal delocalization error. For other quasiparticle energies, their connection to the generalized Kohn-Sham orbital energies has not been established but remains highly interesting. 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. Extensive results with over forty 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 calculations of excitation energies of the $N$-electron systems from the ground state DFA calculations of the $\left(N-1\right)$-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.