Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

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Low-temperature spin-polarized scanning tunneling microscopy is employed to study spin transport across single Cobalt-Phathalocyanine molecules adsorbed on well characterized magnetic nanoleads. A spin-polarized electronic resonance is identified over the center of the molecule and exploited to spatially resolve stationary spin states. These states reflect two molecular spin orientations and, as established by density functional calculations, originate from a ferromagnetic molecule-lead superexchange interaction mediated by the organic ligands. 73.20.At,75.70.Rf,85.65.+h Conceptually new device structures accounting for sizable quantum effects will be needed if the downscaling of electronic and magnetic devices were to continue. One of these new concepts is the marriage of molecular electronics and spintronics, where functional molecules become active device components within a circuitry where information is carried by spins [1,2]. Progress toward this tantalizing goal rely on our understanding of spin transport and magnetism in reduced dimensions, where fundamental playgrounds extend to the extreme limit of single atoms and molecules. Studies include spin transport across a well chosen molecule sandwiched between two magnetic leads [3,4], or even atomic-size constrictions formed by bringing two leads into contact [5,6]. One of the limiting drawbacks is the variability of the resulting conductance, which comes from the incomplete knowledge we have of the molecule-lead interface. For instance, only a few experimental studies have focused on the interaction between a molecular spin and a magnetic substrate [7,8]. A better understanding would enable us to target the chemical engineering needed for building the desired spintronic functionalities into a molecule. In the past years, it became possible with spin-polarized (SP) scanning tunneling microscopy and spectroscopy (STM and STS) to directly observe the interplay between magnetism and surface structure with atomic resolution. SP-STM can also serve as a model tunneling magnetoresistance device since the junction includes two well defined magnetic leads -the tip and the sampleseparated by a vacuum barrier. A link can then be accurately established between spin transport and density of states. Recently, through SP-STM it was possible to evidence how the magnetization switching of a nanocluster is influenced by the spatial location of the spin injection [9]. Another example can be found in SP-STM of single atoms [10]. When the SP current flows across a magnetic atom adsorbed on a magnetic surface rather than directly into the surface, the tunneling spin transport is significantly affected, and some control can be exerted through the choice of the atom.Here we show how tunneling spin transport can be modified by "dressing" atoms with organic ligands. We combine low-temperature SP-STM and model calculations to study a model system consisting of individual Cobalt-Phthalocyanine (CoPc, Fig. 1a) molecules adsorbed on a magnetic substrate. The interaction between the m...

We investigate how field-effect doping affects the structural properties, the electronic structure and the Hall coefficient of few-layers transition metal dichalcogenides by using density-functional theory. We consider mono-, bi-, and trilayers of the H polytype of MoS2, MoSe2, MoTe2, WS2, and WSe2 and provide a full database of electronic structures and Hall coefficients for hole and electron doping. We find that, for both electron and hole doping, the electronic structure depends on the number of layers and cannot be described by a rigid band shift. Furthermore, it is important to relax the structure under the asymmetric electric field. Interestingly, while the width of the conducting channel depends on the doping, the number of occupied bands at each given k point is almost uncorrelated with the thickness of the doping-charge distribution. Finally, we calculate within the constant-relaxation-time approximation the electrical conductivity and the inverse Hall coefficient. We demonstrate that in some cases the charge determined by Hall-effect measurements can deviate from the real charge by up to 50%. For hole-doped MoTe2 the Hall charge has even the wrong polarity at low temperature. We provide the mapping between the doping charge and the Hall coefficient. In the appendix we present more than 250 band structures for all doping levels of the transition-metal dichalcogenides considered within this work.