Benchmarking van der Waals functionals with noncontact RPA calculations on graphene-Ag(111)

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).We have benchmarked long range behavior of seven different van der Waals functionals comparing them with our ACF-RPA correlation calculations for graphene on a Ag(111) system. Correlation given by the second version of van der Waals density functional vdW-DF2 agrees remarkably well with our random phase approximation (RPA) calculation in the long range region. In the intermediate and shorter range regions combining vdW-DF2 correlation with proper exchange functional becomes important. We compared the results of the van der Waals functionals in this region to the previous RPA calculations and to some extent to experimental observations, and calculated that the combined vdW-DF2(C09x) or rev-vdW-DF2 functionals show satisfactory behavior.Peer Reviewe

Benchmarking van der Waals functionals with noncontact RPA calculations on graphene-Ag(111)

We have benchmarked long range behavior of seven different van der Waals functionals comparing them with our ACF-RPA correlation calculations for graphene on a Ag(111) system. Correlation given by the second version of van der Waals density functional vdW-DF2 agrees remarkably well with our random phase approximation (RPA) calculation in the long range region. In the intermediate and shorter range regions combining vdW-DF2 correlation with proper exchange functional becomes important. We compared the results of the van der Waals functionals in this region to the previous RPA calculations and to some extent to experimental observations, and calculated that the combined vdW-DF2(C09x) or rev-vdW-DF2 functionals show satisfactory behavior

Femtosecond laser driven molecular dynamics on surfaces: Photodesorption of molecular oxygen from Ag(110)

We simulate the femtosecond laser induced desorption dynamics of a diatomic molecule from a metal surface by including the effect of the electron and phonon excitations created by the laser pulse. Following previous models, the laser induced surface excitation is treated through the two temperature model, while the multidimensional dynamics of the molecule is described by a classical Langevin equation, in which the friction and random forces account for the action of the heated electrons. In this work, we propose the additional use of the generalized Langevin oscillator model to also include the effect of the energy exchange between the molecule and the heated surface lattice in the desorption dynamics. The model is applied to study the laser induced desorption of O$_2$ from the Ag(110) surface, making use of a six-dimensional potential energy surface calculated within density functional theory. Our results reveal the importance of the phonon mediated process and show that, depending on the value of the electronic density in the surroundings of the molecule adsorption site, its inclusion can significantly enhance or reduce the desorption probabilities.Comment: 11 pages, 8 figure

Strong two-dimensional plasmon in Li-intercalated hexagonal boron-nitride film with low damping

The field of plasmonics seeks to find materials with an intensive plasmon (large plasmon pole weight) with low Landau, phonon and other losses (small decay width). In this paper we propose a new class of materials that show exceptionally good plasmonic properties. These materials consist of van der Waals stacked 'plasmon active' layers (atomically thin metallic layers) and 'supporting' layers (atomically thin wide band gap insulating layers). One such material that can be experimentally realized - lithium intercalated hexagonal boron-nitride is studied in detail. We show that its 2D plasmon intensity is superior to intensity of well studied Dirac plasmon in heavy doped graphene which is hard to achieve. We also propose the method for computationally very cheap, but accurate analysis of plasmon spectra in such materials, based on one band tight-binding approach and effective background dielectric function

Proximity-induced magnetization in graphene: Towards efficient spin gating

Gate-tunable spin-dependent properties could be induced in graphene at room temperature through magnetic proximity effect by placing it in contact with a metallic ferromagnet. Because strong chemical bonding with the metallic substrate makes gating ineffective, an intervening passivation layer is needed. Previously considered passivation layers result in a large shift of the Dirac point away from the Fermi level, so that unrealistically large gate fields are required to tune the spin polarization in graphene. We show that a monolayer of Au or Pt used as the passivation layer between Co and graphene brings the Dirac point closer to the Fermi level. In the \Co/\Pt/\Gr system the proximity-induced spin polarization in graphene and its gate control are strongly enhanced by the presence of a surface band near the Fermi level. Furthermore, the shift of the Dirac point could be eliminated entirely by selecting submonolayer coverage in the passivation layer. Our findings open a path towards experimental realization of an optimized two-dimensional system with gate-tunable spin-dependent properties.Comment: 10 page

Crystal structure prediction of (quasi-)two-dimensional lead halide perovskites

Two-dimensional lead halide perovskites are promising materials for optoelectronics due to the tunability of their properties with the number of lead halide layers and the choice of an organic spacer. Physical understanding for the rational design of materials primarily requires knowledge of crystal structure. 2D lead halide perovskites are usually prepared in the form of films complicating the experimental determination of structure. To enable theoretical studies of experimentally unresolvable structures as well as high-throughput virtual screening, we present an algorithm for crystal structure prediction of lead halide perovskites. Using automatically prepared classical potential we show that our algorithm enables fast access to a structure that can be used for further first-principles studies

Mechanochemical Metathesis between AgNO3 and NaX (X = Cl, Br, I) and Ag2XNO3 Double-Salt Formation

Here we describe real-time, in situ monitoring of mechanochemical solid-state metathesis between silver nitrate and the entire series of sodium halides, on the basis of tandem powder X-ray diffraction and Raman spectroscopy monitoring. The mechanistic monitoring reveals that reactions of AgNO3 with NaX (X = Cl, Br, I) differ in reaction paths, with only the reaction with NaBr providing the NaNO3 and AgX products directly. The reaction with NaI revealed the presence of a novel, short-lived intermediate phase, while the reaction with NaCl progressed the slowest through the well-defined Ag2ClNO3 intermediate double salt. While the corresponding iodide and bromide double salts were not observed as intermediates, all three are readily prepared as pure compounds by milling equimolar mixtures of AgX and AgNO3. The in situ observation of reactive intermediates in these simple metathesis reactions reveals a surprising resemblance of reactions involving purely ionic components to those of molecular organic solids and cocrystals. This study demonstrates the potential of in situ reaction monitoring for mechanochemical reactions of ionic compounds as well as completes the application of these techniques to all major compound classes