Chapter 3
Electronic Structure Theory for X-Ray
Absorption and Photoemission
Spectroscopy
Peter Krüger
Abstract The principles of X-ray absorption and photoemission spectroscopy calculations are introduced and the basics of electronic structure theory, including the
Hartree–Fock approximation, density functional theory, its time-dependent version
and quasiparticle theory are reviewed on an elementary level. Emphasis is put on
polarization effects and the role played by electron correlation.
3.1 Introduction
In this chapter, the basic theory of X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES) is introduced and popular computational methods
are reviewed. Since XAS and PES mainly probe electronic excitations, a thorough
understanding of electronic structure theory is mandatory. We shall review the standard theoretical methods for ground state electronic structure calculations, namely,
Hartree–Fock (HF) and density functional theory (DFT). Among the various excited
state theories, we focus on time-dependent DFT and briefly touch upon Green’s
function quasiparticle methods and the Bethe–Salpeter equation approach. We do
not discuss ligand-field atomic multiplet theory, because this important method for
transition metal L-edge calculations is covered in Chap. 4.
3.2 Light–Matter Interaction
As light is an electromagnetic wave, it interacts with all charged particles. In the
visible to X-ray regime, the interaction with the electrons hugely dominates the
interaction with the atomic nuclei. We shall therefore disregard the nuclear degrees
P. Krüger (B)
Graduate School of Engineering and Molecular Chirality Research Center, Chiba University,
Chiba 263-8522, Japan
e-mail: pkruger@chiba-u.jp
© The Author(s) 2021
H. Bulou et al. (eds.), Magnetism and Accelerator-Based Light Sources,
Springer Proceedings in Physics 262,
https://doi.org/10.1007/978-3-030-64623-3_3
63
Electronic Structure Theory for X-Ray
Absorption and Photoemission
Spectroscopy
Peter Krüger
Abstract The principles of X-ray absorption and photoemission spectroscopy calculations are introduced and the basics of electronic structure theory, including the
Hartree–Fock approximation, density functional theory, its time-dependent version
and quasiparticle theory are reviewed on an elementary level. Emphasis is put on
polarization effects and the role played by electron correlation.
3.1 Introduction
In this chapter, the basic theory of X-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES) is introduced and popular computational methods
are reviewed. Since XAS and PES mainly probe electronic excitations, a thorough
understanding of electronic structure theory is mandatory. We shall review the standard theoretical methods for ground state electronic structure calculations, namely,
Hartree–Fock (HF) and density functional theory (DFT). Among the various excited
state theories, we focus on time-dependent DFT and briefly touch upon Green’s
function quasiparticle methods and the Bethe–Salpeter equation approach. We do
not discuss ligand-field atomic multiplet theory, because this important method for
transition metal L-edge calculations is covered in Chap. 4.
3.2 Light–Matter Interaction
As light is an electromagnetic wave, it interacts with all charged particles. In the
visible to X-ray regime, the interaction with the electrons hugely dominates the
interaction with the atomic nuclei. We shall therefore disregard the nuclear degrees
P. Krüger (B)
Graduate School of Engineering and Molecular Chirality Research Center, Chiba University,
Chiba 263-8522, Japan
e-mail: pkruger@chiba-u.jp
© The Author(s) 2021
H. Bulou et al. (eds.), Magnetism and Accelerator-Based Light Sources,
Springer Proceedings in Physics 262,
https://doi.org/10.1007/978-3-030-64623-3_3
63