[en] The realistic description of correlated electron systems took an important step forward a few years ago as the combination of density functional methods and dynamical mean-field theory was conceived. This framework allows access to both high and low energy physics and is capable of the description of the specific physics of strongly correlated materials, like the Mott metal-insulator transition. A very important step in the procedure is the interface between the band structure method and the dynamical mean-field theory and its impurity solver. We present a general interface between a projector augmented-wave-based density functional code and many-body methods based on Wannier functions obtained from a projection on local orbitals. The implementation is very flexible and allows for various applications. Quantities like the momentum-resolved spectral function are accessible. We present applications to SrVO₃ and the metal-insulator transition in Ca_2-xSr_xRuO₄.

[en] When exploring new materials for their potential in (opto)electronic device applications, it is important to understand the role of various carrier interaction and scattering processes. In atomically thin transition metal dichalcogenide semiconductors, the Coulomb interaction is known to be much stronger than in quantum wells of conventional semiconductors like GaAs, as witnessed by the 50 times larger exciton binding energy. The question arises, whether this directly translates into equivalently faster carrier–carrier Coulomb scattering of excited carriers. Here we show that a combination of ab initio band-structure and many-body theory predicts Coulomb-mediated carrier relaxation on a sub-100 fs time scale for a wide range of excitation densities, which is less than an order of magnitude faster than in quantum wells. (letter)

[en] Artificially assembled linear atomic clusters, CoCu_nCoCu_m, are used to explore variations of the Kondo effect at the two Co sites. For all investigated Cu_n chain lengths () the addition of a single Cu atom to one edge Co atom of the chain () strongly reduces the amplitude of the Abrikosov–Suhl–Kondo resonance of that Co atom. Concomitantly, the resonance line width is more than halved. On the contrary, the Kondo effect of the opposite edge Co atom remains unaffected. Hybridization together with the linear geometry of the cluster are likely to drive the effect. (paper)

[en] Using ab initio calculations we reveal the nature of the insulating phase recently found experimentally in monolayer 1T-NbSe₂. We find soft phonon modes in a large part of the Brillouin zone indicating the strong-coupling nature of a charge-density-wave instability. Structural relaxation of a supercell reveals a Star-of-David reconstruction with an energy gain of 60 meV per primitive unit cell. The band structure of the distorted phase exhibits a half-filled flat band which is associated with orbitals that are delocalized over several atoms in each Star of David. By including many-body corrections through a combined GW, hybrid-functional, and DMFT treatment, we find the flat band to split into narrow Hubbard bands. The lowest energy excitation across the gap turns out to be between itinerant Se-p states and the upper Hubbard band, determining the system to be a charge-transfer insulator. Combined hybrid-functional and GW calculations show that long-range interactions shift the Se-p states to lower energies. Thus, a delicate interplay of local and long-range correlations determines the gap nature and its size in this distorted phase of the monolayer 1T-NbSe₂. (paper)

[en] In order for methods combining ab initio density-functional theory and many-body techniques to become routinely used, a flexible, fast, and easy-to-use implementation is crucial. We present an implementation of a general charge self-consistent scheme based on projected localized orbitals in the projector augmented wave framework in the Vienna Ab Initio Simulation Package. We give a detailed description on how the projectors are optimally chosen and how the total energy is calculated. We benchmark our implementation in combination with dynamical mean-field theory: first we study the charge-transfer insulator NiO using a Hartree–Fock approach to solve the many-body Hamiltonian. We address the advantages of the optimized against non-optimized projectors and furthermore find that charge self-consistency decreases the dependence of the spectral function—especially the gap—on the double counting. Second, using continuous-time quantum Monte Carlo we study a monolayer of SrVO₃, where strong orbital polarization occurs due to the reduced dimensionality. Using total-energy calculation for structure determination, we find that electronic correlations have a non-negligible influence on the position of the apical oxygens, and therefore on the thickness of the single SrVO₃ layer. (paper)

[en] Phthalocyanine molecules have been adsorbed to Ir(111) and to graphene on Ir(111). From a comparison of scanning tunneling microscopy images of individual molecules adsorbed to the different surfaces alone it is difficult to discern potential differences in the molecular adsorption geometry. In contrast, vibrational spectroscopy using inelastic electron scattering unequivocally hints at strong molecule deformations on Ir(111) and at a planar adsorption geometry on graphene. The spectroscopic evidence for the different adsorption configurations is supported by density functional calculations

[en] We present a joint theoretical and experimental investigation of charge doping and electronic potential landscapes in hybrid structures composed of graphene and semiconducting single layer molybdenum disulfide (MoS₂). From first-principles simulations, we find electron doping of graphene due to the presence of rhenium impurities in MoS₂. Furthermore, we show that MoS₂ edges give rise to charge reordering and a potential shift in graphene, which can be controlled through external gate voltages. The interplay of edge and impurity effects allows the use of the graphene-MoS₂ hybrid as a photodetector. Spatially resolved photocurrent signals can be used to resolve potential gradients and local doping levels in the sample