The GW Compendium: A Practical Guide to Theoretical Photoemission Spectroscopy

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.

Calculation of core‐level electron spectra of ionic liquids

“…When the order of BEs is essential, the ΔKS method or, even better, the GW method should be used. [ 39,69,70 ] Nonetheless, because the ε(1s) method is computationally cheaper and more accessible, it can also be used for predicting the XPS spectra of larger systems as well as in longer simulations, especially with periodic boundary conditions. The GW or ΔKS methods are currently impractical for large systems.…”

From flat to tilted: gradual interfaces in organic thin film growth

“…Inclusion of 20 −40 % of exact exchange in the DFT functional is essential for an accurate description of the electronic structure of π-conjugated organic systems and for an accurate prediction of their molecular arrangement. [77][78][79] Highly accurate G 0 W 0 calculations, 80 also performed with CP2K 81,82 for a thiophene monomer, confirm that the PBE0 functional yields the correct energetic ordering of the HOMO, HOMO-1 and lowest unoccupied orbital (LUMO), see Table S1 (SI). This gives us confidence that the predicted HOMO densities and computed STM images of α-6T layers are qualitatively correct.…”

Tuning the Bandgap Character of Quantum‐Confined Si–Sn Alloyed Nanocrystals

“…To obtain quasiparticle energies, starting from a G 0 W 0 , a ev GW calculation was performed where the quasiparticle energies were updated in the noninteracting Green's function while the wavefunctions were kept fixed at their mean‐field values. [ 42 ] The quasiparticle energies were converged until their mean‐change dropped below 10 −5 a.u. For the GW calculation the generalized plasmon pole model (PPM) of the dielectric response frequency dependence [ 38 ] with a screening cutoff energy of 9 a.u.…”

“…But one should note that the PPM assumes a single charge‐neutral excitation and is mainly applied to periodic (crystalline) systems, for finite systems, however, the excitations are not necessarily collective thus the PPM is not rigorously justified here. [ 42 ] However, in practice it has been show that the generalized PPM calculations perform well also for molecular systems. [ 43 ] Moreover, the systems studied here, while still finite, are tending already toward bulk and are somewhere in between molecules and bulk, thus the applicability of generalized PPM is justified.…”