The band gap of periodically-doped graphene with hydrogen is investigated. It is found through a tight-binding model (TB) that for certain periodicities, called here NGPs (non-gap periodicities), no gap is opened at the Dirac point. This result is confirmed by Density Functional Theory (DFT) calculations. DFT results show that a tiny gap is opened for NGPs due to exchange effects, not taken into account in the TB model. However, this tiny gap is one or two orders of magnitude smaller than the gap opened for other periodicities different from NGPs. This finding opens up a new path for band gap engineering experiments in graphene.
We investigate the effects of Na adsorption on the electronic structure of bare and Ir cluster superlattice covered epitaxial graphene on Ir(111) using angle-resolved photoemission spectroscopy and scanning tunneling microscopy. At Na saturation coverage a massive charge migration from sodium atoms to graphene raises the graphene Fermi level by about 1.4 eV relative to its neutrality point. We find that Na is adsorbed on top of the graphene layer and when coadsorbed onto an Ir cluster superlattice it results in the opening of a large bandgap of Δ = 740 meV comparable to the one of Ge and with …
The electronic and structural properties of (i) boron doped graphene sheets, and (ii) the chemisorption processes of hydrogen adatoms on the boron doped graphene sheets have been examined by {\it ab initio} total energy calculations.
We present a first-principles study of geometrical structure and energetics of hydrogen adsorbed on hexagonal single-walled silicon nanotubes (SiNTs). The adsorption behaviors of hydrogen molecules in SiNTs are investigated. The binding energies for the most stable physisorbed configurations are calculated to be less than 0.1 eV. The energy barriers are also investigated for dissociation of H2 molecules. Finally, we consider encapsulation of H2 molecules in SiNTs. The possibility of SiNTs as hydrogen storage materials is discussed.
Hydrogen is a promising element for applications in new energy sources like fuel cells. One key issue for such applications is storing hydrogen. And, to improve storage capacity, understanding the interaction mechanism between hydrogen and possible storage materials is critical. This work uses DFT simulations to comprehensively investigate the adsorption mechanism of H/H$_2$ on the 2D metallic porphyrins with one transition metal in its center. Our results suggest that the mechanism for adsorption of H (H$_2$) is chemisorption (physisorption). The maximum adsorption energy for atomic hydrogen …
The hydrogen adsorption sites in MOF5 were determined using neutron powder diffraction along with first-principles calculations. The metal-oxide cluster is primarily responsible for the adsorption while the organic linker plays only a secondary role. Equally important, at low temperatures and high-concentration, H2 molecules form unique interlinked high-symmetry nano-clusters with intermolecular distances as small as 3.0 Ang. and H2-uptake as high as 10-wt%. These results hold the key to optimizing MOF materials for hydrogen storage applications and also suggest that MOFs can be used as templa…
wo-dimensional (2D) materials unique properties and their promising applications in post-silicon microelectronics have attracted significant attention in the past decade. Recently, ferromagnetic order with out-of-plane easy axis in a monolayer of CrI3 has been observed and reported, with a Curie temperature of 45 K. Here we study, using density functional theory (DFT) calculations, how hydrogen and oxygen adsorption affects the structural, electronic, and magnetic properties of a CrI3 monolayer. Our results show that while the structure remains almost unchanged by the adsorption of hydrogen, a…
Adsorption of hydrogen atoms on a single graphite sheet (graphene) has been investigated by first-principles electronic structure means, employing plane-wave based, periodic density functional theory. A reasonably large 5x5 surface unit cell has been employed to study single and multiple adsorption of H atoms. Binding and barrier energies for sequential sticking have been computed for a number of configurations involving adsorption on top of carbon atoms. We find that binding energies per atom range from ~0.8 eV to ~1.9 eV, with barriers to sticking in the range 0.0-0.2 eV. In addition, depend…
Static and dynamic changes induced by adsorption of atomic hydrogen on the NiAl(110) lattice at 130 K have been examined as a function of adsorbate coverage. Adsorbed hydrogen exists in three distinct phases. At low coverages the hydrogen is itinerant because of quantum tunneling between sites and exhibits no observable vibrational modes. Between 0.4 ML and 0.6 ML, substrate mediated interactions produce an ordered superstructure with c(2x2) symmetry, and at higher coverages, hydrogen exists as a disordered lattice gas. This picture of how hydrogen interacts with NiAl(110) is developed from ou…
Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes of the hydrogen molecule on the Mg(0001) surface. It is found that during the dissociative adsorption process with the minimum energy barrier, the hydrogen molecule firstly orients perpendicular, and then rotates to be parallel to the surface. It is also found that the orientation of the hydrogen molecule at the transition state is neither perpendicular nor parallel to the surface. Most importantly, we find that the rotation causes a reduction of the calculated dissociation ene…
Density functional theory $(DFT)$ studies show that doping of $3d TM$ atoms into $Mg_4^{0,+} (TMMg_3^{0,+})$ can alter the endothermic nature of molecular hydrogen adsorption on bare $Mg_4^{0,+}$. $H_2$ adsorption on $TMMg_3^{0,+}$ clusters depends on the $TM(3d)$ orbital contribution to the frontier molecular orbitals of the clusters. In $H_2TMMg_3^{0,+}$ complexes, $H_2$ is adsorbed through donation and back donation of electronic charges with $TMMg_3^{0,+}$ clusters. $H_2$ binding energy is the maximum for $NiMg_3$ (-0.76 eV) and $FeMg_3^+$ (-0.48 eV) among the neutral and cationic $TMMg_3$…
We present a detailed ab initio study of the electronic structure and magnetic order of an Fe monolayer on the Ir(001) surface covered by adsorbed oxygen and hydrogen. The results are compared to the clean Fe/Ir(001) system, where recent intensive studies indicated a strong tendency towards an antiferromagnetic order and complex magnetic structures. The adsorption of an oxygen overlayer significantly increases interlayer distance between the Fe layer and the Ir substrate, while the effect of hydrogen is much weaker. We show that the adsorption of oxygen (and also of hydrogen) leads to a p(2$\t…
By using first principles calculations we report a chemical doping induced gap in graphene. The structural and electronic properties of CrO$_3$ interacting with graphene layer are calculated using ab initio methods based on the density functional theory. The CrO$_3$ acts as an electron acceptor modifying the original electronic and magnetic properties of the graphene surface through a chemical adsorption. The changes induced in the electronic properties are strongly dependent of the CrO$_3$ adsorption site and for some sites it is possible to open a gap in the electronic band structure. Spin p…
While the diffusion of hydrogen on silicon surfaces has been relatively well characterised both experimentally and theoretically, the diffusion around corners between surfaces, as will be found on nanowires and nanostructures, has not been studied. Motivated by nanostructure fabrication by Patterned Atomic Layer Epitaxy (PALE), we present a density functional theory (DFT) study of the diffusion of hydrogen around the edge formed by the orthogonal (001) and (110) surfaces in silicon. We find that the barrier from (001) to (110) is approximately 0.3 eV lower than from (110) to (001), and that it…
First-principles DFT levels of calculations have been carried out in order to study the structural stability and electronic properties of hydrogen passivated graphene (H-graphene) clusters. Two different shaped clusters, rectangular and circular, consisting of 6 to 160 carbon atoms and hydrogen termination at the zigzag boundary edges have been studied. The relative stability of rectangular shaped cluster consisting 96 C-atoms found to be 1.5% greater than that of circular shape cluster consisting same number of C-atoms. In comparing circular and rectangular cluster containing same number of C…
We investigated interaction between hydrogen molecules and bare as well as functionalized single-wall carbon nanotubes (SWNT) using first-principles plane wave method. We found that the binding energy of the H$_{2}$ physisorbed on the bare SWNT is very weak, and can be enhanced neither by increasing the curvature of the surface through radial deformation, nor by the coadsorption of Li atom that makes the semiconducting tube metallic. Though the bonding is strengthened upon adsorption directly to Li atom, yet its nature continues to be physisorption. However, the character of the bonding change…
The structural, vibrational, energetic and electronic properties of hydrogen at the stoichiometric RuO2(110) termination are studied using density functional theory. The oxide surface is found to stabilize both molecular and dissociated H2. The most stable configuration in form of hydroxyl groups (monohydrides) at the undercoordinated O^br surface anions is at low temperatures accessed via a molecular state at the undercoordinated Ru^cus atoms (dihydrogen) and a second precursor in form of a water-like species (dihydride) at the O^br sites. This complex picture of the low-temperature dissociat…
The adsorption of hydrogen at nonpolar GaN(1-100) surfaces and its impact on the electronic and vibrational properties is investigated using surface electron spectroscopy in combination with density functional theory (DFT) calculations. For the surface mediated dissociation of H2 and the subsequent adsorption of H, an energy barrier of 0.55 eV has to be overcome. The calculated kinetic surface phase diagram indicates that the reaction is kinetically hindered at low pressures and low temperatures. At higher temperatures ab-initio thermodynamics show, that the H-free surface is energetically fav…
We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)$^S$. Lactide is a precursor for polylactic acid ring-opening polymerization and Pt is a well known catalyst surface. We study here the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using Density Functional Theory (DFT…
Graphene functionalization by hydrogen and fluorine has been proposed as a route to modulate its reactivity and electronic properties. However, until now, proposed systems present degradation and limited hydrogen adsorption capacity. In this study, combining first-principles calculations based on density functional theory (DFT) and reactive molecular dynamics, we analyze the tuning of hydrogen adsorption and electronic properties in fluorinated and hydrogenated monolayer graphenes. Our results indicate that fluorine adsorption promotes stronger carbon$-$hydrogen bonds. By changing the concentr…
We investigate the electron transfer from a dissociatively adsorbed H2 molecule to a Au(111) surface using the first-principles methods. A fractional electron transfers from a molecule to a substrate, and potential energy increases during the process. The initial energy increase coincides with that of the isolated, separated, and positively charged H2 molecule calculated by the real-space density functional method. The barrier formation is due to the destabilization of the molecule induced by the electron transfer. The electronegativity difference between the adsorbate and the substrate determ…
Adsorption of ammonia at NH3/NH2/H covered GaN(0001) surface was analyzed using results of ab initio calculations. The whole configuration space of partially NH3/NH2/H covered GaN(0001) surface was divided into zones differently pinned Fermi level: at Ga broken bond state for dominantly bare surface (region I), at VBM for NH2 and H covered (region II), and at CBM for NH3 covered surface (region III). The extensive ab intio calculations show validity of electron counting rule (ECR) for all mixed coverage, for bordering these three regions. The adsorption was analyzed using newly identified depe…
We studied the interaction between a single hydrogen atom and a single graphene using classical molecular dynamics simulation with modified Brenner REBO potential. Three interactions, which are adsorption, reflection, penetration, were observed. Overhang structure appears and creates an adsorption site on the backside of the graphene. It is considered that backside adsorption occurs under the two conditions that an incident hydrogen atom should have incident energy which is larger than the potential barrier of a hexagonal hole of the graphene and that after the hydrogen atom passes through the…
We have carried out first-principles calculations of Be(0001) thin films to study the oscillatory quantum size effects exhibited in the surface energy, work function, and binding energy of the atomic hydrogen monolayer adsorption. The prominent enhancement of the surface density of states at the Fermi level makes Be(0001) thin films more metallic compared to the crystalline Be. As a result, the calculated energetics of Be films and the properties of atomic H adsorption onto Be(0001) surface are featured by a quantum oscillatory behavior. Furthermore, The prominent change in the Be(0001) surfac…
We investigate the hydrogen adsorption capacity of Na-coated carbon nanotubes (Na-SWCNTs) using first-principles electronic structure calculations at absolute temperature and pressure. A single Na atom is always found to occupy the hollow site of a hexagonal carbon ring in all the six different SWCNTs considered, with a nearly uniform Na-C bond length of 2.5 A. Semiconducting zigzag nanotubes, (8,0) and (5,0), show stronger binding energies for the Na atom (-2.1 eV and -2.6 eV respectively), as compared to metallic SWCNTs with armchair and chiral geometries. The single Na atom can further adso…
We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H$_2$ adsorption is dissociative with no energy barrier while other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8-wt% hydrogen. The system is quite stable and exhibits associative desorption upon heating, a requirement for reversible storage. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nan…
The adsorption of hydrogen on the polar Zn-ended ZnO(0001) surface has been investigated by density functional {\it ab-initio} calculations. An on top H(1x1) ordered overlayer with genuine H-Zn chemical bonds is shown to be energetically favorable. The H covered surface is metallic and spin-polarized, with a noticeable magnetic moment at the surface region. Lower hydrogen coverages lead to strengthening of the H-Zn bonds, corrugation of the surface layer and to an insulating surface. Our results explain experimental observations of hydrogen adsorption on this surface, and not only predict a me…
Enhancing Hydrogen Adsorption Ability of MOF-5 with Metal Node Exchange and Linker Functionalisation
Carl von Ossietzky Universität Oldenburg（奥尔登堡卡尔·冯·奥西茨基大学）；Friedrich-Schiller Universität Jena（耶拿弗里德里希·席勒大学）；Université de Montpellier, CNRS, ENSCM（蒙彼利埃大学，法国国家科学研究中心，国立化学学院）
We present a first-principles study of the atomic hydrogen adsorption onto the Be(10\={1}0) thin film. There are two types of Be(10\={1}0) surfaces according to the interlayer spacing between the surface and its nearest-neighbor layer. We show that the H adsorption features on these two kinds of surfaces are remarkably different. The work function, averaged electrostatic potential, and the local charge density consistently show that the charge is transferred from H to Be for L-type (see the text below) surfaces, while the transfer process is inverted for S-type surfaces.
Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released effi…
Hydrogen adsorption on graphene in commensurate periodic arrangements leads to bandgap opening at the Dirac point and the emergence of dispersionless midgap bands. We study these bandgap effects and their dependence on periodicity for a single hydrogen adsorbate on periodic graphene supercells using spin-polarized density-functional theory calculations. Our results show that for certain periodicities, marked by a scale factor of three, the bandgap is suppressed to a great extent, and has a special level structure around the neutrality point. We present explanations for the origin of the change…
We have performed first-principles studies on adsorption patterns of hydrogen adatoms on uniaxially strained graphene. Our simulation reveals that the adsorption energy of adatoms are sensitive to the strain. Hydrogen adatoms on zigzag strained graphene tend to form a chain-like adsorption patterns perpendicular to the strain direction, but those under armchair strain cannot form any long-range chain pattern. We explain our results in terms of a tight-binding model and the electronic structure of strained graphene. These anisotropic adsorption behaviors under uniaxial strain suggest methods fo…
We show that the electronic and atomic structure of carbon nanotubes undergo dramatic changes with hydrogen chemisorption from first principle calculations. Upon uniform exohydrogenation at half coverage, the cross sections of zigzag nanotubes become literally square or rectangular, and they are metallic with very high density of states at the Fermi level, while other isomers can be insulating. For both zigzag and armchair nanotubes, hydrogenation of each carbon atom from inside and outside alternatively yield the most stable isomer with a very weak curvature dependence and a large band gap.
We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage and adsorption sites. In the coverage range $0<Θ<1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendecy to the formation of H isl…
Grand Canonical Monte Carlo (GCMC) simulations are performed to study hydrogen physisorption in different nano carbon porous materials made up of different substructures including carbon nanotubes (CNT), graphene sheets and C60. Hydrogen weight percentage (wt%) at different temperatures with pressure ranging from 1 to 20MPa are predicted. Fugacity and quantum effects on hydrogen adsorption are investigated. Different structural dimensions including the sizes of the substructures and spacing between the substructures are used to study the geometrical effects on hydrogen storage capacity in carb…
We use the non-interacting tight-binding model to study the effect of isolated hydrogen adsorbates on the quasiparticle spectra of single-layer graphene. Using the Green's function approach, we obtain analytic expressions for the local density of states and the spectral function of hydrogen-doped graphene, which are also numerically evaluated and plotted. Our results are relevant for the interpretation of scanning tunneling microscopy and angle-resolved photoemission spectroscopy data of functionalized graphene.
Ni/Cu(001) is known as a unique system showing the spin-reorientation transition from an in-plane to out-of-plane magnetization direction when the Ni-overlayer thickness is increased. We investigate different relaxed multilayer structures with a hydrogen adlayer using the full-potential linearized augmented plane-wave method. The relaxed geometries, determined by total energy and atomic force calculations, show that H-monolayer strongly influences the interlayer distance between the Ni-surface and sub-surface layers yielding the outward relaxation of Ni-layer at H/Ni interface. Furthermore, la…
The d-band center descriptor based on the adsorption strength of adsorbate has been widely used in understanding and predicting the catalytic activity in various metal catalysts. However, its applicability is unsure for the single-atom-anchored two-dimensional (2D) catalysts. Here, taking the hydrogen (H) adsorption on the single-atom-anchored 2D basal plane as example, we examine the influence of orbitals interaction on the bond strength of hydrogen adsorption. We find that the adsorption of H is formed mainly via the hybridization between the 1s orbital of H and the vertical dz2 orbital of a…
We have carried out first-principles calculation of Mg(0001) free-standing thin films to study the oscillatory quantum size effect exhibited in the surface energy, work function, interlayer relaxation, and adsorption energy of the atomic hydrogen adsorbate. The quantum well states have been shown. The calculated energetics and interlayer relaxation of clean and H-adsorbed Mg films are clearly featured by quantum oscillations as a function of the thickness of the film, with oscillation period of about 8 monolayers, consistent with recent experiments. The calculated quantum size effect in H adso…
We measure the adsorption height of hydrogen-intercalated quasi-free-standing monolayer graphene on the (0001) face of 6H silicon carbide by the normal incidence x-ray standing wave technique. A density functional calculation for the full ($6 \sqrt{3} \times 6 \sqrt{3}$)-R30$^\circ$ unit cell, based on a van der Waals corrected exchange correlation functional, finds a purely physisorptive adsorption height in excellent agreement with experiments, a very low buckling of the graphene layer, a very homogeneous electron density at the interface and the lowest known adsorption energy per atom for g…
The graphane with chemically bonded alkali metals (Li, Na, K) was considered as potential material for hydrogen storage. The ab initio calculations show that such material can adsorb as many as 4 hydrogen molecules per Li, Na and K metal atoms. These values correspond to 12.20 wt%, 10.33 wt% and 8.56 wt% of hydrogen, respectively and exceed the DOE requirements. The thermodynamic analysis shows that Li-graphane complex is the most promising for hydrogen storage with ability to adsorb 3 hydrogen molecules per metal atom at 300 K and pressure in the range from 5 to 250 atm.
Halogenated aromatic molecules assemble on surfaces forming both hydrogen and halogen bonds. Even though these systems have been intensively studied on flat metal surfaces, high-index vicinal surfaces remain challenging, as they may induce complex adsorbate structures. The adsorption of 2,6-dibromoanthraquinone (2,6-DBAQ) on flat and stepped gold surfaces is studied by means of van der Waals corrected density functional theory. Equilibrium geometries and corresponding adsorption energies are systematically investigated for various different adsorption configurations.~It is shown that bridge si…
Effect of hydrogen adsorption on the extraordinary Hall phenomenon (EHE) in ferromagnetic CoPd films is studied as a function of composition, thickness, substrate and hydrogen concentration in atmosphere. Adsorption of hydrogen adds a positive term in the extraordinary Hall effect coefficient and modifies the perpendicular magnetic anisotropy with the respective changes in coercivity and remanence of hysteresis loops. Hydrogen sensitive compositions are within the Co concentration range 20% < x < 50% with the strongest response near the EHE polarity reversal point x_0 ~ 38%. Depending on the f…
The relationship between activated H2 bond length and adsorption distance on MXenes identified with graph neural network and resonating valence bond theory
The dissociative adsorption of hydrogen on Pd(100) has been studied by ab initio quantum dynamics and ab initio molecular dynamics calculations. Treating all hydrogen degrees of freedom as dynamical coordinates implies a high dimensionality and requires statistical averages over thousands of trajectories. An efficient and accurate treatment of such extensive statistics is achieved in two steps: In a first step we evaluate the ab initio potential energy surface (PES) and determine an analytical representation. Then, in an independent second step dynamical calculations are performed on the analy…
The adsorption of an alkali-metal submonolayer on graphene occupying every third hexagon of the honeycomb lattice in a commensurate $(\sqrt{3}\times\sqrt{3})R30^\circ$ arrangement induces an energy gap in the spectrum of graphene. To exemplify this type of band gap, we present \textit{ab initio} density functional theory calculations of the electronic band structure of C$_6$Li. An examination of the lattice geometry of the compound system shows the possibility that the nearest-neighbor hopping amplitudes have alternating values constructed in a Kekulé-type structure. The band structure of the …
Due to the improvement of computer power and the development of efficient algorithms it is now possible to combine high-dimensional quantum dynamical calculations of the dissociative adsorption of molecular beams with reliable ab-initio potential energy surfaces (PES). In this brief review two recent examples of such studies of the systems H_2/Cu(111), where adsorption is hindered by a noticeable energy barrier, and H_2/Pd(100), where activated as well as non-activated paths to adsorption exist, are presented. The effect of lateral surface corrugations on the sticking probability in the tunnel…
Hydrogen embrittlement of metals is widely observed, but its atomistic origins remain little understood and much debated. Combining a unique identification of interstitial sites through polyhedral tessellation and first-principles calculations, we study hydrogen adsorption at grain boundaries in a variety of face-centered cubic metals of Ni, Cu, gamma-Fe and Pd. We discover the chemomechanical origin of variation of adsorption energetics for interstitial hydrogen at grain boundaries. A general chemomechanical formula is established to provide accurate assessments of hydrogen trapping and segre…
