Computational methods for 2D materials modelling.

Materials with thickness ranging from a few nanometers to a single atomic layer present unprecedented opportunities to investigate new phases of matter constrained to the two-dimensional plane. Particle-particle Coulomb interaction is dramatically affected and shaped by the dimensionality reduction, driving well-established solid state theoretical approaches to their limit of applicability. Methodological developments in theoretical modelling and computational algorithms, in close interaction with experiments, led to the discovery of the extraordinary properties of two-dimensional materials, such as high carrier mobility, Dirac cone dispersion and bright exciton luminescence, and inspired new device design paradigms. This review aims to describe the computational techniques used to simulate and predict the optical, electronic and mechanical properties of two-dimensional materials, and to interpret experimental observations. In particular, we discuss in detail the particular challenges arising in the simulation of two-dimensional constrained fermions and quasiparticles, and we offer our perspective on the future directions in this field.

Communication: electronic band gaps of semiconducting zig-zag carbon nanotubes from many-body perturbation theory calculations.

Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy.

Infrared spectroscopy of copper-resveratrol complexes: a joint experimental and theoretical study.

Infrared multiple-photon dissociation spectroscopy has been used to record vibrational spectra of charged copper-resveratrol complexes in the 3500-3700 cm(-1) and 1100-1900 cm(-1) regions. Minimum energy structures have been determined by density functional theory calculations using plane waves and pseudopotentials. In particular, the copper(I)-resveratrol complex presents a tetra-coordinated metal bound with two carbon atoms of the alkenyl moiety and two closest carbons of the adjoining resorcinol ring. For these geometries vibrational spectra have been calculated by using linear response theory. The good agreement between experimental and calculated IR spectra for the selected species confirms the overall reliability of the proposed geometries.

Tunable band gap in hydrogenated quasi-free-standing graphene.

We show by angle-resolved photoemission spectroscopy that a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via hydrogen loading and reaches approximately 1.0 eV for a hydrogen coverage of 8%. The local rehybridization from sp(2) to sp(3) in the chemical bonding is observed by X-ray photoelectron spectroscopy and X-ray absorption and allows for a determination of the amount of chemisorbed hydrogen. The hydrogen induced gap formation is completely reversible by annealing without damaging the graphene. Calculations of the hydrogen loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission experiments. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study hydrogen storage in carbon materials.

The addition of plerixafor is safe and allows adequate PBSC collection in multiple myeloma and lymphoma patients poor mobilizers after chemotherapy and G-CSF.

We report 13 multiple myeloma (MM) or lymphoma patients who were failing PBSC mobilization after disease-specific chemotherapy and granulocyte-CSF (G-CSF), and received plerixafor to successfully collect PBSCs. Patients were considered poor mobilizers when the concentration of PB CD34(+) cells was always lower than 10 cells/µL, during the recovery phase after chemotherapy and/or were predicted to have inadequate PBSC collection to proceed to autologous transplantation. Plerixafor (0.24 mg/kg) was administered subcutaneously for up to three consecutive days, while continuing G-CSF, 10-11 h before the planned leukapheresis. Plerixafor administration was safe and no significant adverse events were recorded. We observed a 4.7 median fold-increase in the number of circulating CD34(+) cells after plerixafor as compared with baseline CD34(+) cell concentration (from a median of 6.2 (range 1-12) to 21.5 (range 9-88) cells/µL). All patients collected >2 × 10(6) CD34(+) cells/kg in 1-3 leukaphereses. In all, 5/13 patients have already undergone autograft with plerixafor-mobilized PBSCs, showing a rapid and durable hematological recovery. Our results suggest that the pre-emptive addition of plerixafor to G-CSF after chemotherapy is safe and may allow the rescue of lymphoma and MM patients, who need autologous transplantation but are failing PBSC mobilization.

Ab initio melting curve of molybdenum by the phase coexistence method.

Ab initio calculations of the melting curve of molybdenum for the pressure range 0-400 GPa are reported. The calculations employ density functional theory (DFT) with the Perdew-Burke-Ernzerhof exchange-correlation functional in the projector augmented wave (PAW) implementation. Tests are presented showing that these techniques accurately reproduce experimental data on low-temperature body-centered cubic (bcc) Mo, and that PAW agrees closely with results from the full-potential linearized augmented plane-wave implementation. The work attempts to overcome the uncertainties inherent in earlier DFT calculations of the melting curve of Mo, by using the "reference coexistence" technique to determine the melting curve. In this technique, an empirical reference model (here, the embedded-atom model) is accurately fitted to DFT molecular dynamics data on the liquid and the high-temperature solid, the melting curve of the reference model is determined by simulations of coexisting solid and liquid, and the ab initio melting curve is obtained by applying free-energy corrections. The calculated melting curve agrees well with experiment at ambient pressure and is consistent with shock data at high pressure, but does not agree with the high-pressure melting curve deduced from static compression experiments. Calculated results for the radial distribution function show that the short-range atomic order of the liquid is very similar to that of the high-T solid, with a slight decrease of coordination number on passing from solid to liquid. The electronic densities of states in the two phases show only small differences. The results do not support a recent theory according to which very low dT(m)dP values are expected for bcc transition metals because of electron redistribution between s-p and d states.