We present the GW100 set. GW100 is a benchmark set of the ionization potentials and electron affinities of 100 molecules computed with the GW method using three independent GW codes and different GW methodologies. The quasi-particle energies of the highest-occupied molecular orbitals (HOMO) and lowest-unoccupied molecular orbitals (LUMO) are calculated for the GW100 set at the G0W0@PBE level using the software packages TURBOMOLE, FHI-aims, and BerkeleyGW. The use of these three codes allows for a quantitative comparison of the type of basis set (plane wave or local orbital) and handling of unoccupied states, the treatment of core and valence electrons (all electron or pseudopotentials), the treatment of the frequency dependence of the self-energy (full frequency or more approximate plasmon-pole models), and the algorithm for solving the quasi-particle equation. Primary results include reference values for future benchmarks, best practices for convergence within a particular approach, and average error bars for the most common approximations.

No abstract

Hot carrier thermalization is a major source of efficiency loss in solar cells. Because of the subpicosecond time scale and complex physics involved, a microscopic characterization of hot carriers is challenging even for the simplest materials. We develop and apply an ab initio approach based on density functional theory and many-body perturbation theory to investigate hot carriers in semiconductors. Our calculations include electron-electron and electron-phonon interactions, and require no experimental input other than the structure of the material. We apply our approach to study the relaxation time and mean free path of hot carriers in Si, and map the band and k dependence of these quantities. We demonstrate that a hot carrier distribution characteristic of Si under solar illumination thermalizes within 350 fs, in excellent agreement with pump-probe experiments. Our work sheds light on the subpicosecond time scale after sunlight absorption in Si, and constitutes a first step towards ab initio quantification of hot carrier dynamics in materials. DOI: 10.1103/PhysRevLett.112.257402 PACS numbers: 78.56.-a, 71.20.Mq, 78.47.db, 88.40.H-Single-junction solar cells based on crystalline Si are rapidly approaching the Shockley-Queisser efficiency limit [1,2]. While the Carnot efficiency of ∼95% sets the ultimate limit for solar energy conversion at room temperature, practical efficiency limits in ordinary photovoltaic (PV) solar cells are significantly lower; e.g., the ShockleyQueisser limit for Si is close to 30% [2]. The main factors limiting efficiency are carrier thermalization and absorption losses [3,4]. For the case of Si under AM1.5 solar illumination [5], nearly 25% of incident solar energy is lost to heat as the nonequilibrium ("hot") carriers generated by sunlight absorption thermalize to the edges of the band gap. Not only is hot carrier thermalization the main source of loss in most PV materials, it is also difficult to prevent, control, and understand with microscopic detail due to the subpicosecond time scale typical of hot carrier relaxation [6]. This scenario is common to other technologies employing hot carriers, including electronics, optoelectronics, and renewable energy devices beyond PV [7][8][9][10][11].The leading mechanisms involved in hot carrier thermalization consist of inelastic electron-phonon (e-ph) and electron-electron (e-e) scattering processes [12]. Relaxation times for e-ph and e-e interactions in semiconductors have been studied extensively by model Hamiltonians with selected phonon modes, simplified electronic band structures, deformation potentials, and/or empirical pseudopotentials [13][14][15][16][17][18]. Hot carrier dynamics in semiconductors has been investigated experimentally using pump-probe optical measurements [19,20].This work has two main goals. First, we present an ab initio approach based on density functional theory (DFT) and many-body perturbation theory to investigate hot carriers in materials. Second, we apply this framework to study hot carrier thermalization a...

We calculate the photoemission spectra of suspended and epitaxial doped graphene using an ab initio cumulant expansion of the Green's function based on the GW self-energy. Our results are compared to experiment and to standard GW calculations. For doped graphene on a silicon carbide substrate, we find, in contrast to earlier calculations, that the spectral function from GW only does not reproduce experimental satellite properties. However, ab initio GW plus cumulant theory combined with an accurate description of the substrate screening results in good agreement with experiment, but gives no plasmaron (i.e., no extra well-defined excitation satisfying Dyson's equation).

We compute the phase diagram of twisted bilayer graphene near the magic angle where the occurrence of flat bands enhances the effects of electron-electron interactions and thus unleashes strongly-correlated phenomena. Most importantly, we find a crossover between d+id superconductivity and Mott insulating behavior near half-filling of the lowest electron band when the temperature is increased. This is consistent with recent experiments. Our results are obtained using unbiased many-body renormalization group techniques combined with a mean-field analysis of the effective couplings.Introduction-The discovery of correlated-insulator behaviour [1] and unconventional superconductivity (SC) in twisted bilayer graphene (TBG) by Cao et al. [2] has triggered an intense research effort to understand the phase diagram as well as other physical properties [3, 4] of this system. TBG is a van der Waals material consisting of two graphene layers which are rotated with respect to each other. At certain magic values of the rotation or twist angle, the Fermi velocity at the Dirac points of TBG vanishes resulting in flat bands in the vicinity of the Fermi energy [5,6]. For such a system, it is expected that electron-electron interactions play an important role and could potentially lead to the emergence of exotic correlated phases. The unveiling of this type of unconventional superconductivity and Mott physics in TBG is particularly exciting due to its resemblance to the physics of high-T c superconductors. In fact, the reported ratio [2] of the superconducting critical temperature to the Fermi temperature -a hallmark to decide whether superconductors are in the strong or weak coupling limit -puts experimentally realized TBG near the magic angle in the ballpark of those ratios obtained for high-T c cuprates (LSCO,YBCO,BSCCO), iron pnictides or monolayer iron selenide on a STO surface. These reside among the strongest coupling superconductors known today. Thus, TBG provides an intriguing route to study the largely unknown physics of such a superconductor in the extremely controllable framework offered by graphene where the ratio of the interaction to the kinetic energy can be tuned by approaching the magic twist angle and the filling can be modified by a bottom gate.To gain insight into the experimental results of Cao et al. [1,2], a wide range of models have been proposed in recent weeks [7]. Without assuming a specific microscoping pairing mechanism, Peltonen and coworkers [8] used mean-field theory to study SC in TBG and find a strongly inhomogeneous superconducting order parameter. Ray and Das [9] solve the Eliashberg equation for TBG and predict an extended s-wave as the leading pairing symmetry. In contast, Xu and Balents [10], Zhang

Core-electron x-ray photoelectron spectroscopy is a powerful technique for studying the electronic structure and chemical composition of molecules, solids and surfaces. However, the interpretation of measured spectra and the assignment of peaks to atoms in specific chemical environments is often challenging. Here, we address this problem and introduce a parameter-free computational approach for calculating absolute core-electron binding energies. In particular, we demonstrate that accurate absolute binding energies can be obtained from the total energy difference of the ground state and a state with an explicit core hole when exchange and correlation effects are described by a recently developed meta-generalized gradient approximation and relativistic effects are included even for light elements. We carry out calculations for molecules, solids and surface species and find excellent agreement with available experimental measurements. For example, we find a mean absolute error of only 0.16 eV for a reference set of 103 molecular core-electron binding energies. The capability to calculate accurate absolute core-electron binding energies will enable new insights into a wide range of chemical surface processes that are studied by x-ray photoelectron spectroscopy. arXiv:1904.04823v1 [cond-mat.mtrl-sci]

The ability to understand and control the electronic properties of individual molecules in a device environment is crucial for developing future technologies at the nanometre scale and below. Achieving this, however, requires the creation of three-terminal devices that allow single molecules to be both gated and imaged at the atomic scale. We have accomplished this by integrating a graphene field effect transistor with a scanning tunnelling microscope, thus allowing gate-controlled charging and spectroscopic interrogation of individual tetrafluoro-tetracyanoquinodimethane molecules. We observe a non-rigid shift in the molecule's lowest unoccupied molecular orbital energy (relative to the Dirac point) as a function of gate voltage due to graphene polarization effects. Our results show that electron–electron interactions play an important role in how molecular energy levels align to the graphene Dirac point, and may significantly influence charge transport through individual molecules incorporated in graphene-based nanodevices.

Harnessing hot electrons and holes resulting from the decay of localized surface plasmons in nanomaterials has recently led to new devices for photovoltaics, photocatalysis and optoelectronics. Properties of hot carriers are highly tunable and in this work we investigate their dependence on the material, size and environment of spherical metallic nanoparticles. In particular, we carry out theoretical calculations of hot carrier generation rates and energy distributions for six different plasmonic materials (Na, K, Al, Cu, Ag and Au). The plasmon decay into hot electron-hole pairs is described via Fermi's Golden Rule using the quasistatic approximation for optical properties and a spherical well potential for the electronic structure. We present results for nanoparticles with diameters up to 40 nm, which are embedded in different dielectric media. We find that small nanoparticles with diameters of 16 nm or less in media with large dielectric 1 arXiv:1802.05096v1 [cond-mat.mtrl-sci] 14 Feb 2018 constants produce most hot carriers. Among the different materials, Na, K and Au generate most hot carriers. We also investigate hot-carrier induced water splitting and find that simple-metal nanoparticles are useful for initiating the hydrogen evolution reaction, while transition-metal nanoparticles produce dominantly holes for the oxygen evolution reaction. Keywordshot electrons, plasmon decay, nanoparticles, water splitting, nanophotonics Energetic or "hot" electrons and holes produced by the decay of localized surface plasmons (LSP) in metallic nanostructures have recently generated much excitement. They can be harnessed in optoelectronic devices, such as photodetectors, or for solar energy conversion, i.e. in photocatalytic or photovoltaic devices. 1-8 For example, Mukherjee et al. observed that plasmon-induced hot electrons can trigger H 2 dissociation reactions on the surface of gold nanoparticles. 9 An important advantage of nanoplasmonic devices compared to traditional systems is their tunability: their optical and electronic properties depend sensitively on the nanoparticle size and shape, but also on the nanoparticle material and its environment. 10-15To guide experimental progress and identify nano-devices with favorable hot-carrier properties, a detailed theoretical understanding of the physico-chemical processes that govern hot-carrier generation is needed. However, developing such a theory is challenging because of the large size of experimentally relevant nanoparticles. Atomistic ab initio calculations are currently only feasible for metallic clusters and very small nanoparticles. 5,16,17 To model properties of experimentally relevant nanoparticles with radii of 10 nm or more, two different strategies have been employed. In many calculations, simplified models for the electronic structure of the nanoparticle are used, such as jellium models or non-interacting electron models. 18-21 For example, Manjavacas et al. employed a spherical well model to simulate hot-carrier generation in silver nanoparticles with di...