Density Functional Prediction of Quasiparticle, Excitation, and Resonance Energies of Molecules With a Global Scaling Correction Approach.

Xiaolong Yang,Weitao Yang,Xiao Zheng

doi:10.3389/fchem.2020.588808

Abstract

Molecular quasiparticle and excitation energies determine essentially the spectral characteristics measured in various spectroscopic experiments. Accurate prediction of these energies has been rather challenging for ground-state density functional methods, because the commonly adopted density function approximations suffer from delocalization error. In this work, by presuming a quantitative correspondence between the quasiparticle energies and the generalized Kohn–Sham orbital energies, and employing a previously developed global scaling correction approach, we achieve substantially improved prediction of molecular quasiparticle and excitation energies. In addition, we also extend our previous study on temporary anions in resonant states, which are associated with negative molecular electron affinities. The proposed approach does not require any explicit self-consistent field calculation on the excited-state species, and is thus highly efficient and convenient for practical purposes.

Highlights

Density function theory (DFT) (Hohenberg and Kohn, 1964) has made great success in practical calculations for ground-state electronic properties because of its outstanding balance between accuracy and computational cost
Quasihole Energies of Molecules Because of the lack of highly accurate experimental or theoretical data for the molecular quasielectron energies, in this work we only compare the calculated quasihole energies that are associated with the occupied KS/generalized KS (GKS) orbitals to the reference data available in the literature
A non-empirical global scaling correction (GSC) approach is used to reduce the delocalization error associated with the density functional approximations (DFAs) by imposing an energy linearity condition for systems with a fractional number of electrons

Summary

Introduction

Density function theory (DFT) (Hohenberg and Kohn, 1964) has made great success in practical calculations for ground-state electronic properties because of its outstanding balance between accuracy and computational cost. Vext(r) is the external potential, vH(r) is the Hartree potential, vxc(r) is the local exchange-correlation (XC) potential, and {φm(r)} and {εm} are the KS/generalized KS (GKS) orbitals and their eigenvalues, respectively. It is challenging to apply conventional ground-state density functional methods to calculate excited-state-related properties, such as the quasiparticle (QP) energies and the electronic excitation energies, which will be introduced as follows. In a direct photoemission experiment, an electron on a molecule absorbs the energy of a photon and gets excited away from the molecule. Such a process leaves a quasihole in the molecule whose energy level is renormalized by the presence of the other electrons. In an inverse photoemission experiment, an electron attaches to a molecule by emitting a photon, which leads to the formation of a quasielectron whose energy level is influenced by the existing electrons in the molecule (Onida et al, 2002)

Methods

Results

Conclusion