Abstract

The GW approximation in electronic structure theory has become a widespread tool for predicting electronic excitations in chemical compounds and materials. In the realm of theoretical spectroscopy, the GW method provides access to charged excitations as measured in direct or inverse photoemission spectroscopy. The number of GW calculations in the past two decades has exploded with increased computing power and modern codes. The success of GW can be attributed to many factors: favorable scaling with respect to system size, a formal interpretation for charged excitation energies, the importance of dynamical screening in real systems, and its practical combination with other theories. In this review, we provide an overview of these formal and practical considerations. We expand, in detail, on the choices presented to the scientist performing GW calculations for the first time. We also give an introduction to the many-body theory behind GW, a review of modern applications like molecules and surfaces, and a perspective on methods which go beyond conventional GW calculations. This review addresses chemists, physicists and material scientists with an interest in theoretical spectroscopy. It is intended for newcomers to GW calculations but can also serve as an alternative perspective for experts and an up-to-date source of computational techniques.

Highlights

  • Electronic structure theory derives from the fundamental laws of quantum mechanics and describes the behavior of electrons—the glue that shapes all matter

  • Before we introduce the GW approximation as a tractable computational approach for calculating quasiparticle energies, we will first address the photocurrent, which is the quantity measured in direct photoemission experiments

  • The accuracy of the Analytic continuation (AC) approach depends on the features of the self-energy on the real axis and on the flexibility of the model function, which continues the self-energy to real frequencies

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Summary

INTRODUCTION

Electronic structure theory derives from the fundamental laws of quantum mechanics and describes the behavior of electrons—the glue that shapes all matter. To understand the properties of matter and the behavior of molecules, the quantum mechanical laws must be solved numerically because a pen and paper solution is not possible In this context, Hedin’s GW method (Hedin, 1965) has become the de facto standard for electronic structure properties as measured by direct and inverse photoemission experiments, such as quasiparticle band structures and molecular excitations. Electronic structure theory covers the quantum mechanical spectrum of computational materials science and quantum chemistry. The GW approach is an integral part of electronic structure theory and readily available in major electronic structure codes It is taught at summer schools along side DFT and other electronic structure methods.

Direct and Inverse Photoemission
The Quasiparticle Concept
Comparison to Experimental Spectra
HEDIN’S GW EQUATIONS
The G0W0 Equations
Procedure
Frequency Treatment
Contour Deformation
Analytic Continuation
Fully Analytic Approach
Comparison of Accuracy and Computational
Basis Sets
Plane Waves
Localized Basis Sets
Pseudopotentials
Basis Set Convergence
Elimination of Unoccupied State
Starting Point Dependence and Optimization
Consistent Starting Point Scheme
Deviation From the Straight Line Scheme
IP-Theorem Schemes
Computational Complexity and Cost
Practical Guidelines
Fully Self-consistent GW
Eigenvalue Self-consistency and Level
Self-consistency via a New Ground
SOLIDS
Band Gaps
Band Structures and Band Parameters
Lifetimes
More Challenging Solids
Defects in Solids
Outlook on Solids
SURFACES
TWO-DIMENSIONAL MATERIALS
MOLECULES
First Ionization Potentials and Electron
Ionization Spectra
The GW100 Benchmark Set
Molecular Crystals
10. TOTAL ENERGY AND THE ELECTRONIC GROUND STATE
10.1. Electron Density
10.2. Total Energy
11.1. Challenges
11.2. Quantum Chemistry
11.3. Non-equilibrium Green’s Functions
11.4. Vertex Corrections
11.5. Optical Properties
11.6. T-Matrix
11.7. Cumulant Expansion
11.8. Local Vertex
12. CONCLUSION
Green’s Function Formalism
Findings
Hedin’s Equations

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