1,720,990 research outputs found
Diffusion quantum monte carlo study of argon dimer
No full textWe reproduce the binding energy curve of a prototypical van derWaals system, namely the Ar dimer, by a fixed node-diffusion quantum Monte Carlo approach. The results, in good agreement with the experimental values and the best reference potential-energy curve, are compared with those obtained by density functional theory (DFT) using different local, semilocal, and van der Waals-corrected functionals. A differential-density analysis is also reported, which describes how the electron density redistributes as a consequence of the interaction between the Ar atoms and highlights significant differences among the different approaches and possible shortcomings of DFT methods in accurately describing the electron density distribution
Bandgap opening in graphene using alkali ions by first principles
No full textRecently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na thorn, K thorn, and Cs thorn ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene
Introduction to Maximally Localized Wannier Functions
No full textThe maximally localized Wannier functions (MLWFs) provide a practical basis set for the analysis and computation of the electronic structure of periodic systems, which can be applied in all those cases where real space localization represents a significant advantage. In close analogy with MLWFs, localized molecular orbitals (LMOs) have a long tradition in computational chemistry. To provide a simple and practical introduction to MLWFs, this chapter reviews the basic ideas underlying periodic lattices and Bloch functions. Among the potentially infinite applications of MLWFs, a number of selected examples are presented in the chapter, providing a practical and intuitive solution to common problems in electronic structure calculations. These encompass the classical cases of charge distribution and bonding analysis, followed by the closely related study of defected and amorphous structures, where information on bonding and electronic charge distribution complements the standard geometrical analysis of the system
Cooperative Effects of N-Doping and Ni(111) Substrate for Enhanced Chemical Reactivity of Graphene: The Case of CO and O2 Adsorption
No full textWhile pristine graphene (G) is chemically inert, chemical doping is currently regarded as a leading strategy for fine-tuning both G electronic properties and reactivity toward adsorbed species. Following recent experimental work, we demonstrate that deposition of G on Ni(111) and introduction of N-based defects in the G lattice lead to cooperative effects, determining sizeable chemical reactivity toward CO adsorption. CO chemisorption is predicted on pyridinic-, pyrrolic-, and epoxy-like defects generated by N-ion bombardment, compatibly with the experiment. Comparison with O-2 adsorption further reveals selective reactivity of the defective system with respect to distinct gaseous moieties, thereby opening new pathways toward high-sensitivity CO sensors and controlled surface chemical reactions
Prediction for Two Spatially Modulated Superfluids: 4He on Fluorographene and on Hexagonal BN
No full textWe have derived the adsorption potential of 4He atoms on fluorographene (GF), on graphane and on hexagonal boron nitride (hBN) by a recently developed ab initio method that incorporates the van der Waals interaction. The stability of the commensurate R30 degrees phase of 4He on GF and on hBN is studied by state-of-the-art quantum simulations at T=0 K. With our adsorption potentials, we find that in both cases this commensurate state of 4He is unstable toward a fluid state in which the 4He atoms are delocalized, and not localized like in the case of 4He on graphite or on graphene. In the case of GF, the present result is in qualitative agreement with the superfluid phase that was obtained using an empirical adsorption potential (Nava et al. in Phys Rev B 86:174509, 2012). This fluid state of 4He on GF and on hBN is characterized by a very large density modulation. For instance, the local density changes by a factor of order 2 along the path connecting two adsorption sites. Recent experiments (Nyeki et al. in Nat Phys 13:455, 2017) have discovered a superfluid phase in the second layer 4He. This is a spatially modulated superfluid that turns out to have anomalous thermal properties. This gives a strong motivation for an experimental study of monolayer 4He on GF and on hBN that we predict to be a superfluid with a much stronger spatial modulation
Many-body van der Waals interactions beyond the dipole approximation
No full textLong-ranged van der Waals (vdW) interactions are most often treated via Lennard-Jones approaches based on the combination of two-body and dipolar approximations. While beyond-dipole interactions and many-body contributions were separately addressed, little is known about their combined effect, especially in large molecules and relevant nanoscale systems. Here, we provide a full many-body description of vdW interactions beyond the dipole approximation, efficiently applicable to large-scale systems. Dipole-quadrupole interactions consistently exhibit large magnitude up to nm-scale separations, while many-body effects lead to system-dependent screening effects, which can reduce vdW interactions by a large fraction. Combined many-body and multipolar terms emerge as an essential ingredient for the reliable description of vdW interactions in molecular and nanoscale systems
Tunable van der Waals interactions in low-dimensional nanostructures
No full textNon-covalent van der Waals interactions play a major role at the nanoscale, and even a slight change in their asymptotic decay could produce a major impact on surface phenomena, self-assembly of nanomaterials, and biological systems. By a full many-body description of vdW interactions in coupled carbyne-like chains and graphenic structures, here, we demonstrate that both modulus and a range of interfragment forces can be effectively tuned, introducing mechanical strain and doping (or polarizability change). This result contrasts with conventional pairwise vdW predictions, where the two-body approximation essentially fixes the asymptotic decay of interfragment forces. The present results provide viable pathways for detailed experimental control of nanoscale systems that could be exploited both in static geometrical configurations and in dynamical processes
Amino-silane co-functionalized h-BN nanofibers with anti-corrosive function for epoxy coating
No full textIn this research, hexagonal boron nitride nanofibers co-functionalized with polydopamine and (3-aminopropyl) triethoxysilane (Fh-BNNFs) are used for developing anti-corrosion solvent-based nanocomposite epoxy coatings. The h-BNNFs are successfully synthesized by utilizing inexpensive precursors of melamine and boric acid. The prepared nanomaterials are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and N2 adsorption/desorption isotherms. The corrosion resistance of the pure and nanocomposite epoxy coatings is investigated by electrochemical impedance spectroscopy, Potentiodynamic polarization tests, salt spray, and pull-off adhesion measurements. The results indicate that the epoxy nanocomposite coatings containing optimum amount of the Fh-BNNFs show superior corrosion resistance. Moreover, density functional theory (DFT) method is applied to investigate the energetics and interaction mechanisms at each interface within the epoxy matrix
A review of zirconium disulfide: Structural characterization, properties, applications, and prospects of dichalcogenide materials
No full textIn recent decades, two-dimensional (2D) materials have attracted significant attention for their unique electronic, optical, mechanical, and electrical properties, making them promising for applications in catalysis, solar cells, batteries, and superconductivity. Among 2D materials, transition-metal dichalcogenides (TMDCs) are noteworthy due to their tunable bandgap, high carrier mobility, and mechanical flexibility. Zirconium disulfide (ZrS2), a member of the TMDC family, stands out for its thermodynamic stability, environmental friendliness, and excellent thermoelectric properties. This paper provides an in-depth discussion of the synthesis of ZrS2 and its related materials, detailing various crystal structures and characterization methods. Additionally, the properties and applications of ZrS2 and its analogs are thoroughly reviewed, with a focus on their potential future developments
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