Showing papers on "Electronic structure published in 2009"
TL;DR: In this paper, the electronic structure of GNRs and GQDs with 2-20 nm lateral dimensions was verified by tunnelling spectroscopy, and it was shown that GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width, and the magnitudes of measured GNR energy gaps agree with recent theoretical calculations.
Abstract: Graphene shows promise as a future material for nanoelectronics owing to its compatibility with industry-standard lithographic processing, electron mobilities up to 150 times greater than Si and a thermal conductivity twice that of diamond. The electronic structure of graphene nanoribbons (GNRs) and quantum dots (GQDs) has been predicted to depend sensitively on the crystallographic orientation of their edges; however, the influence of edge structure has not been verified experimentally. Here, we use tunnelling spectroscopy to show that the electronic structure of GNRs and GQDs with 2-20 nm lateral dimensions varies on the basis of the graphene edge lattice symmetry. Predominantly zigzag-edge GQDs with 7-8 nm average dimensions are metallic owing to the presence of zigzag edge states. GNRs with a higher fraction of zigzag edges exhibit a smaller energy gap than a predominantly armchair-edge ribbon of similar width, and the magnitudes of the measured GNR energy gaps agree with recent theoretical calculations.
1,199 citations
TL;DR: The results of this detailed analysis reveal that the GO is rough with an average surface roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from sp3 C-O bonds.
Abstract: We elucidate the atomic and electronic structure of graphene oxide (GO) using annular dark field imaging of single and multilayer sheets and electron energy loss spectroscopy for measuring the fine structure of C and O K-edges in a scanning transmission electron microscope. Partial density of states and electronic plasma excitations are also measured for these GO sheets showing unusual π* + σ* excitation at 19 eV. The results of this detailed analysis reveal that the GO is rough with an average surface roughness of 0.6 nm and the structure is predominantly amorphous due to distortions from sp3 C−O bonds. Around 40% sp3 bonding was found to be present in these sheets with measured O/C ratio of 1:5. These sp2 to sp3 bond modifications due to oxidation are also supported by ab initio calculations.
1,070 citations
TL;DR: In this paper, the authors reported ab initio calculations of the two-dimensional systems (MoS and NbSe) and compared them with the electronic structure of the three-dimensional analogue of graphene.
Abstract: We report on ab initio calculations of the two-dimensional systems ${\text{MoS}}_{2}$ and ${\text{NbSe}}_{2}$, which recently were synthesized. We find that two-dimensional ${\text{MoS}}_{2}$ is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that ${\text{NbSe}}_{2}$ is a metal, which is similar to the three-dimensional analog of this compound. We further computed the electronic structure of the two-dimensional hexagonal (graphene-like) lattices of Si and Ge and compared them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, also known as silicene, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.
924 citations
Book•
13 Apr 2009
TL;DR: In this article, the authors present an overview of DFT's application in other fields of physics, such as chemistry, physics, and mathematics, as well as its application in the field of surface analysis.
Abstract: Chapter 1: What is Density Functional Theory? 1.1 How To Approach This Book. 1.2 Examples of DFT in Action. 1.3 The Schrodinger Equation. 1.4 Density Functional Theory - From Wavefunctions to Electron Density. 1.5 The Exchange-Correlation Functional. 1.6 The Quantum Chemistry Tourist. 1.7 What Can't DFT Do?. 1.8 Density Functional Theory in Other Fields. 1.9 How To Approach This Book (Revisited). Chapter 2: DFT Calculations for Simple Solids. 2.1 Periodic Structures, Supercells, and Lattice Parameters. 2.2 Face Centered Cubic Materials. 2.3 Hexagonal Close Packed Materials. 2.4 Crystal Structure Prediction. 2.5 Phase Transformations. Chapter 3: Nuts and Bolts of DFT Calculations. 3.1 Reciprocal Space and k-points. 3.2 Energy Cutoffs. 3.3 Numerical Optimization. 3.4 DFT Total Energies - An Iterative Optimization Problem. 3.5 Geometry Optimization. Chapter 4: DFT Calculations for Surfaces of Solids. 4.1 Why Surfaces Are Important. 4.2 Periodic Boundary Conditions and Slab Models. 4.3 Choosing k-points for Surface Calculations. 4.4 Classification of Surfaces by Miller Indices. 4.5 Surface Relaxation. 4.6 Calculation of Surface Energies. 4.7 Symmetric and Asymmetric Slab Models. 4.8 Surface Reconstruction. 4.9 Adsorbates on Surfaces. 4.10 Effects of Surface Coverage. Chapter 5: DFT Calculations of Vibrational Frequencies. 5.1 Isolated Molecules. 5.2 Vibrations of Collections of Atoms. 5.3 Molecules on Surfaces. 5.4 Zero Point Energies. 5.5 Phonons and Delocalized Modes. Chapter 6: Calculating Rates of Chemical Processes Using Transition State Theory. 6.1 A One-Dimensional Example. 6.2 Multi-dimensional Transition State Theory. 6.3 Finding Transition States. 6.4 Finding the Right Transition State. 6.5 Connecting Individual Rates to Overall Dynamics. 6.6 Quantum Effects and Other Complications. Chapter 7: Equilibrium Phase Diagrams From Ab Initio Thermodynamics. 7.1 Stability of Bulk Metal Oxides. 7.2 Stability of Metal and Metal Oxide Surfaces. 7.3 Multiple Chemical Potentials and Coupled Chemical Potentials. Chapter 8: Electronic Structure and Magnetic Properties. 8.1 Electronic Density of States. 8.2 Local DOS and Atomic Charges. 8.3 Magnetism. Chapter 9: Ab Initio Molecular Dynamics. 9.1 Classical Molecular Dynamics. 9.2 Ab Initio Molecular Dynamics. 9.3 Applications of Ab Initio Molecular Dynamics. Chapter 10: Accuracy and Methods Beyond "Standard" Calculations. 10.1 How Accurate Are DFT Calculations? 10.2 Choosing A Functional. 10.3 Examples of Physical Accuracy. 10.4 DFT+X Methods for Improved Treatment of Electron Correlations. 10.5 Large System Sizes With Linear Scaling Methods and Classical Forcefields. 10.6 Conclusion.
852 citations
Posted Content•
TL;DR: In this article, the two-dimensional systems MoS2 and NbSe2 were analyzed and compared with the three-dimensional analogue of this compound, and it was shown that MoS$_2$ is a semiconductor with a gap which is rather close to that of the three dimensional analogue.
Abstract: We report on ab-initio calculations of the two-dimensional systems MoS2 and NbSe2, which recently were synthesized. We find that two-dimensional MoS$_2$ is a semiconductor with a gap which is rather close to that of the three dimensional analogue, and that NbSe$_2$ is a metal, which is similar to the three dimensional analogue of this compound.
We further computed the electronic structure of the two-dimensional hexagonal (graphene like) lattices of Si and Ge, and compare them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.
827 citations
TL;DR: It is found that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B12 clusters and the resultant charge transfer between them.
Abstract: Boron is an element of fascinating chemical complexity. This arises from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons that could in principle favour metallicity, yet they are sufficiently localized to give rise to an insulating state. This delicately balanced electronic structure is easily modified by pressure, temperature and impurities, making it difficult to establish boron's structure and properties. Oganov et al. have now explored the high-pressure behaviour of boron and uncovered a previously unknown ionic phase consisting of negatively charged icosahedral B12 clusters and positively charged B2 pairs. The ionicity of the new phase strongly affects many of its properties, and arises from the different electronic properties of the B12 clusters and B2 pairs and the resultant charge transfer between them. This paper has explored the high-pressure behaviour of boron and uncovered a new phase that consists of negatively charged icosahedral B12 clusters and positively charged B2 pairs. The ionicity of the new phase strongly affects many of its properties, and arises from the different electronic properties of the B12 clusters and B2 pairs and the resultant charge transfer between them. Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new ‘element’ turned out to be a compound containing less than 60–70% of boron, and it was not until 1909 that 99% pure boron was obtained1. And although we now know of at least 16 polymorphs2, the stable phase of boron is not yet experimentally established even at ambient conditions3. Boron’s complexities arise from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high-pressure experiments and ab initio evolutionary crystal structure predictions4,5 that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B12 clusters and the resultant charge transfer between them.
750 citations
TL;DR: Experimental observations of a pressure-induced transformation of Na into an optically transparent phase at ∼200 GPa are reported, attributing the emergence of this dense insulating state not to atom pairing, but to p–d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices.
Abstract: Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behaviour. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals such as lithium (Li; refs 1-3) and sodium (Na; refs 4, 5), leading in turn to structurally complex phases and superconductivity with a high critical temperature. But the most intriguing prediction-that the seemingly simple metals Li (ref. 1) and Na (ref. 4) will transform under pressure into insulating states, owing to pairing of alkali atoms-has yet to be experimentally confirmed. Here we report experimental observations of a pressure-induced transformation of Na into an optically transparent phase at approximately 200 GPa (corresponding to approximately 5.0-fold compression). Experimental and computational data identify the new phase as a wide bandgap dielectric with a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.
661 citations
TL;DR: In this paper, the electron affinity and ionization energy of vacuum-deposited molybdenum trioxide (MoO3) and of a typical MoO3/hole transport material (HTM) interface were determined via ultraviolet and inverse photoelectron spectroscopy.
Abstract: The electronic structures of vacuum-deposited molybdenum trioxide (MoO3) and of a typical MoO3/hole transport material (HTM) interface are determined via ultraviolet and inverse photoelectron spectroscopy. Electron affinity and ionization energy of MoO3 are found to be 6.7 and 9.68 eV, more than 4 eV larger than generally assumed, leading to a revised interpretation of the role of MoO3 in hole injection in organic devices. The MoO3 films are strongly n-type. The electronic structure of the oxide/HTM interface shows that hole injection proceeds via electron extraction from the HTM highest occupied molecular orbital through the low-lying conduction band of MoO3.
640 citations
TL;DR: In this article, the properties of different types of defect states in reduced and n-type doped titania are investigated using density functional theory (DFT) in the local density approximation (LDA) or semilocal generalized gradient approximation (GGA).
Abstract: Defect states in reduced and n-type doped titania are of fundamental importance in several technologically important applications. Still, the exact nature of these states, often referred to as “Ti3+ centers”, is largely unclear and a matter of debate. The problem is complicated by the fact that electronic structure calculations based on density functional theory (DFT) in the local density approximation (LDA) or semilocal generalized gradient approximation (GGA) provide results that do not account for many of the experimentally observed fingerprints of the formation of Ti3+ centers in reduced TiO2. Here, we investigate the properties of at least four different types of Ti3+ centers in bulk anatase, (1) 6-fold-coordinated Ti6c3+ ions introduced by F- or Nb-doping, (2) Ti6c3+−OH species associated with H-doping, (3) undercoordinated Ti5c3+ species associated with oxygen vacancies, and (4) interstitial Ti5c3+ species. The characterization of these different kinds of Ti3+ centers is based on DFT+U and/or hybri...
618 citations
TL;DR: In this paper, the first principles of the electronic structure of BiVO4, a promising photocatalyst for hydrogen generation, were reported, which is a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center.
Abstract: We report the first-principles electronic structure of BiVO4, a promising photocatalyst for hydrogen generation. BiVO4 is found to be a direct band gap semiconductor, despite having band extrema away from the Brillouin zone center. Coupling between Bi 6s and O 2p forces an upward dispersion of the valence band at the zone boundary; however, a direct gap is maintained via coupling between V 3d, O 2p, and Bi 6p, which lowers the conduction band minimum. These interactions result in symmetric hole and electron masses. Implications for the design of ambipolar metal oxides are discussed.
594 citations
TL;DR: In this article, a review of polymer and small molecule-on-metal interfaces with metal is presented, with emphasis placed specifically on the electronic structure and molecular level alignment at these interfaces, perceived differences between small molecule and polymer interfaces, and the difference between organic-onmetal and metal-onorganic interfaces.
Abstract: Considerable research and development means have been focused in the past decade on organic semiconductor thin films and devices with applications to full color displays, flexible electronics and photovoltaics. Critical areas of these thin films are their interfaces with electrodes, with other organic films and with dielectrics, as these interfaces control charge injection and transport through the device. Full understanding of the mechanisms that determine the electronic properties of these interfaces, i.e. the relative position of molecular levels and charge carrier transport states, is an important goal to reach for developing reliable device processing conditions. This report provides an extensive, although probably somewhat biased, review of polymer– and small molecule–metal interface work of the past few years, with emphasis placed specifically on (i) the electronic structure and molecular level alignment at these interfaces, (ii) the perceived differences between small molecule and polymer interfaces, (iii) the difference between organic-on-metal and metal-on-organic interfaces, and (iv) the role played by electrode surface contamination in establishing interface energetics. Environmental conditions, e.g. vacuum vs. ambient, are found to be critical parameters in the processing of polymer and small molecule interfaces with metals. With similar processing conditions, these two types of interfaces are found to obey very similar molecular level alignment rules.
TL;DR: In this article, the surface relaxations, surface energies, and work functions of low-index metallic surfaces using pseudopotential plane-wave density-functional calculations within the generalized gradient approximation were studied.
Abstract: We study the relaxations, surface energies, and work functions of low-index metallic surfaces using pseudopotential plane-wave density-functional calculations within the generalized gradient approximation. We study here the (100), (110), and (111) surfaces of Al, Pd, Pt, and Au and the (0001) surface of Ti, chosen for their use as contact or lead materials in nanoscale devices. We consider clean, mostly nonreconstructed surfaces in the slab-supercell approximation. Particular attention is paid to the convergence of these quantities with respect to slab thickness; furthermore, different methodologies for the calculation of work functions and surfaces energies are compared. We find that the use of bulk references for calculations of surface energies and work functions can be detrimental to convergence unless numerical grids are closely matched, especially when surface relaxations are being considered. Our results and comparison show that calculated values often do not quantitatively match experimental values. This may be understandable for the surface relaxations and surface energies, where experimental values can have large error but even for the work functions, neither local nor semilocal functionals emerge as an accurate choice for every case.
TL;DR: Density functional theory computations on a cluster Au144(SR)60 with an icosahedral Au114 core with 30 RS−Au−SR units protecting its surface yield an excellent fit of the structure factor to the experimental X-ray scattering structure factor measured earlier for 29 kDa thiolate-protected gold clusters.
Abstract: Density-functional theory computations on a cluster Au144(SR)60 with an icosahedral Au114 core with 30 RS−Au−SR units protecting its surface yield an excellent fit of the structure factor to the experimental X-ray scattering structure factor measured earlier for 29 kDa thiolate-protected gold clusters. This cluster has a special combination of atomic and electronic structure that provides explanations for the observed stability and capacitive charging properties with several available oxidation states in electrochemistry and optical absorption extending well into the infrared region.
TL;DR: It is shown that lattice constants, atomization energies of solids, and adsorption energies on metal surfaces evaluated using the random-phase approximation to the correlation energy are in very good agreement with experiment.
Abstract: For ab initio electronic structure calculations, the random-phase approximation to the correlation energy is supposed to be a suitable complement to the exact exchange energy. We show that lattice constants, atomization energies of solids, and adsorption energies on metal surfaces evaluated using this approximation are in very good agreement with experiment. Since the method is fairly efficient and handles ionic, metallic, and van der Waals bonded systems equally well, it is a very promising choice to improve upon density functional theory calculations, without resorting to more demanding diffusion Monte Carlo or quantum chemical methods.
TL;DR: It is found that materials become softer with excitation, and the rate of disordering of the gold lattice is found to be retarded at excitation levels up to 2.85 megajoules per kilogram with respect to the degree of lattice heating, which is indicative of increased lattice stability at high effective electronic temperatures.
Abstract: Under strong optical excitation conditions, it is possible to create highly nonequilibrium states of matter. The nuclear response is determined by the rate of energy transfer from the excited electrons to the nuclei and the instantaneous effect of change in electron distribution on the interatomic potential energy landscape. We used femtosecond electron diffraction to follow the structural evolution of strongly excited gold under these transient electronic conditions. Generally, materials become softer with excitation. In contrast, the rate of disordering of the gold lattice is found to be retarded at excitation levels up to 2.85 megajoules per kilogram with respect to the degree of lattice heating, which is indicative of increased lattice stability at high effective electronic temperatures, a predicted effect that illustrates the strong correlation between electronic structure and lattice bonding.
TL;DR: The fermion functional renormalization-group method is applied to determine the pairing symmetry and pairing mechanism of the FeAs-Based materials and finds an electronic-driven superconducting pairing instability.
Abstract: We apply the fermion functional renormalization-group method to determine the pairing symmetry and pairing mechanism of the FeAs-Based materials. Within a five band model with pure repulsive interactions, we find an electronic-driven superconducting pairing instability. For the doping and interaction parameters we have examined, extended s wave, whose order parameter takes on opposite sign on the electron and hole pockets, is always the most favorable pairing symmetry. The pairing mechanism is the inter-Fermi-surface Josephson scattering generated by the antiferromagnetic correlation.
TL;DR: The results can be rationalized with the help of the valence-bond resonance theory of planar pi conjugated systems and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.
Abstract: 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 5×5 surface unit cell has been adopted to study single and multiple adsorptions 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 to ∼1.9 eV, with barriers to sticking in the range 0.0–0.15 eV. In addition, depending on the number and location of adsorbed hydrogen atoms, we find that magnetic structures may form in which spin density localizes on a 3×3R30° sublattice and that binding (barrier) energies for sequential adsorption increase (decrease) linearly with the site-integrated magnetization. These results can be rationalized with the help of the valence-bond resonance theory of planar π conjugated systems and suggest that preferential sticking due to barrierless adsorption is limited to formation of hydrogen pairs.
TL;DR: In this article, the electronic structure of the recently synthesized hydrogenated graphene, named graphane, was studied using the GW approximation, and the minimum band gap was found to be direct a
Abstract: Using the GW approximation, we study the electronic structure of the recently synthesized hydrogenated graphene, named graphane. For both conformations, the minimum band gap is found to be direct a ...
TL;DR: In this article, it was demonstrated that the presence of the metal substrate leads to a significant polarization of the water bilayer, which causes a substantial water-induced reduction of the work function in spite of the weak water-metal interaction.
Abstract: Properties of the metal–water interface have been addressed by periodic density functional theory calculations, in particular with respect to the electronic and geometric structures of water bilayers on several transition metal surfaces. It will be demonstrated that the presence of the metal substrate leads to a significant polarization of the water bilayer. This causes a substantial water-induced reduction of the work function in spite of the weak water–metal interaction, but it is not associated with a significant change of the electronic structure of the metal substrates. The structure and the vibrational spectra of water bilayers at room temperatures have been studied performing ab initio molecular dynamics simulations. The simulations suggest that the water bilayer structure on noble metals is not stable at room temperature, whereas on more strongly interacting metal surfaces some ordering of the water layer persists. In addition, metal–water interfaces under electrochemical conditions, i.e. for charged metal substrates, are addressed. Our simulations show that the charging of the surface leads to characteristic changes in the wall–oxygen distribution and the vibrational spectra.
TL;DR: In this paper, the formation energies and electronic properties of the most probable isolated defects and their clustered pairs are analyzed through first-principles density functional theory calculations, and the formation of Sn interstitials is found to be higher in energy, under all charge states and chemical environments.
Abstract: Empirically, intrinsic defects in SnO2 are known to give rise to a net oxygen substoichiometry and n-type conductivity; however, the atomistic nature of the defects is unclear. Through first-principles density functional theory calculations, we present detailed analysis of both the formation energies and electronic properties of the most probable isolated defects and their clustered pairs. While stoichiometric Frenkel and Schottky defects are found to have a high energetic cost, oxygen vacancies, compensated through Sn reduction, are predicted to be the most abundant intrinsic defect under oxygen-poor conditions. These are likely to lead to conductivity through the mobility of electrons from Sn(II) to Sn(IV) sites. The formation of Sn interstitials is found to be higher in energy, under all charge states and chemical environments. Although oxygen interstitials have low formation energies under extreme oxygen-rich conditions, they relax to form peroxide ions (O22−) with no possible mechanism for p-type con...
TL;DR: By the first-principles electronic structure calculations, it is found that the ground state of PbO-type tetragonal alpha-FeTe is in a bicollinear antiferromagnetic order, in which the Fe local moments align ferromagnetically along a diagonal direction and antiferronagnetic along the other diagonal direction on the Fe square lattice.
Abstract: By the first-principles electronic structure calculations, we find that the ground state of PbO-type tetragonal alpha-FeTe is in a bicollinear antiferromagnetic order, in which the Fe local moments (similar to 2.5 mu(B)) align ferromagnetically along a diagonal direction and antiferromagnetically along the other diagonal direction on the Fe square lattice. This novel bicollinear order results from the interplay among the nearest, the next-nearest, and the next-next-nearest neighbor superexchange interactions, mediated by Te 5p band. In contrast, the ground state of alpha-FeSe is in a collinear antiferromagnetic order, similar to those in LaFeAsO and BaFe(2)As(2). This finding sheds new light on the origin of magnetic ordering in Fe-based superconductors.
TL;DR: Comparing QDs passivated by different ligands, it is found that hybridized states are denser at the edge of the conduction band of the cluster ligated with phosphine oxide molecules than that with primary amines.
Abstract: We investigate the impact of ligands on the morphology, electronic structure, and optical response of the Cd33Se33 cluster, which overlaps in size with the smallest synthesized CdSe nanocrystal quantum dots (QDs). Our density functional theory calculations demonstrate significant surface reorganization for both the bare cluster and the cluster capped with amine or phosphine oxide model ligands. We observe strong surface−ligand interactions leading to substantial charge redistribution and polarization effects on the surface. These effects result in the development of hybridized states, for which the electronic density is spread over the cluster and the ligands. The loss of one of the passivating ligands leads to either optically dark or bright additional states inside of the band gap, depending on the position of the leaving ligand on the QD surface. However, for fully ligated QDs, neither the ligand-localized nor hybridized molecular orbitals appear as trap states inside or near the band gap of the QD. In...
TL;DR: This work finds that a combination of significantly quantal elements, six of seven atoms being hydrogen, becomes a stable metal at a pressure approximately 1/4 of that required to metalize pure hydrogen itself.
Abstract: From detailed assessments of electronic structure, we find that a combination of significantly quantal elements, six of seven atoms being hydrogen, becomes a stable metal at a pressure approximately 1/4 of that required to metalize pure hydrogen itself. The system, LiH6 (and other LiHn), may well have extensions beyond the constituent lithium. These hypothetical materials demonstrate that nontraditional stoichiometries can considerably expand the view of chemical combination under moderate pressure.
TL;DR: Calculations using density functional theory confirm that structures with on-top registry have the lowest energy and provide clear evidence for strong electronic coupling between the graphene pi-states and Co d-states at the interface.
Abstract: We have grown well-ordered graphene adlayers on the lattice-matched Co(0001) surface. Low-temperature scanning tunneling microscopy measurements demonstrate an on-top registry of the carbon atoms with respect to the Co(0001) surface. The tunneling conductance spectrum shows that the electronic structure is substantially altered from that of isolated graphene, implying a strong coupling between graphene and cobalt states. Calculations using density functional theory confirm that structures with on-top registry have the lowest energy and provide clear evidence for strong electronic coupling between the graphene π-states and Co d-states at the interface.
TL;DR: It is shown that the two orbital branches associated with the 3E excited state are averaged when operating at room temperature, leading to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing.
Abstract: We report a study of the $^{3}E$ excited-state structure of single negatively charged nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at cryogenic temperatures and optically detected magnetic resonance. A theoretical model is developed and shows excellent agreement with experimental observations. In addition, we show that the two orbital branches associated with the $^{3}E$ excited state are averaged when operating at room temperature. This study leads to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing.
TL;DR: It is observed that tunneling from a lower-lying state in hydrogen chloride (HCl) is observed, bolstering the emerging tenet that the coherent interaction between different orbitals—which can amplify the impact of lower orbitals in tunneling processes.
Abstract: Tunneling, one of the most striking manifestations of quantum mechanics, influences the electronic structure of many molecules and solids and is responsible for radioactive decay Much of the interaction of intense light pulses with matter commences with electrons tunneling from atoms or molecules to the continuum Until recently, this starting point was assumed to be the highest occupied orbital of a given system We have now observed tunneling from a lower-lying state in hydrogen chloride (HCl) Analyzing two independent experimental observables allowed us to isolate (via fragment ions), identify (via molecular frame photoelectron angular distributions), and, with the help of ab initio simulations, quantify the contribution of lower-lying orbitals to the total and angle-dependent tunneling current of the molecule Our results bolster the emerging tenet that the coherent interaction between different orbitals—which can amplify the impact of lower orbitals—must be considered in tunneling processes
TL;DR: In this paper, a theoretical study on the electronic structure and elastic transport properties of armchair graphene nanoribbon based junctions is presented by using density functional theory calculations and nonequili...
Abstract: We present a theoretical study on electronic structure and elastic transport properties of armchair graphene nanoribbon based junctions by using density functional theory calculations and nonequili ...
TL;DR: It was theoretically demonstrated that a p-type graphene can be obtained via charge transfer between an organic molecule and graphene, and both the carrier concentration and band gap at the Dirac point can be controlled by coverage of organic molecules.
Abstract: The electronic structure of an electron-acceptor molecule, tetracyanoethylene (TCNE), on graphene was investigated using the first-principles method based on density functional theory. It was theoretically demonstrated that a p-type graphene can be obtained via charge transfer between an organic molecule and graphene. Both the carrier concentration and band gap at the Dirac point can be controlled by coverage of organic molecules. The spin split and partially filled π* orbitals of the TCNE anion radical induce spin density in the graphene layer. Surface modification of graphene by organic molecules could be a simple and effective method to control the electronic structure of graphene over a wide range.
TL;DR: In this article, the electronic band structure and optical properties of Cr-doped ZnO were studied using the density functional method within the generalized-gradient approximation, and three configurations with the substitution of Zn by one and two Cr atoms in different positions were considered.
Abstract: Electronic band structure and optical properties of Cr-doped ZnO were studied using the density functional method within the generalized-gradient approximation. Three configurations with the substitution of Zn by one and two Cr atoms in different positions were considered. For the pure ZnO, the Fermi level locates at the valence band maximum, while it shifts to the conduction band and exhibits metal-like characteristic after Cr atoms are introduced into the ZnO supercell. The calculated optical properties indicate that the optical energy gap is increased after Cr doping. More importantly, strong absorption in the visible-light region is found, which originates from the intraband transition of the Cr 3d bands and the conduction bands. Our calculations provide electronic structure evidence that, in addition to usage as short-wavelength optoelectronic devices, the Cr-doped ZnO system could be a potential candidate for photoelectrochemical application due to the increase in its photocatalytic activity.
TL;DR: The results demonstrate that substitutional P and PN doping creates localized electronic states that modify the electron transport properties by acting as scattering centers, which display promising properties for components in composite materials and, in particular, for fast response and ultra sensitive sensors operating at the molecular level.
Abstract: We present a density functional theory study of the electronic structure, quantum transport and mechanical properties of recently synthesized phosphorus (P) and phosphorus-nitrogen (PN) doped single-walled carbon nanotubes. The results demonstrate that substitutional P and PN doping creates localized electronic states that modify the electron transport properties by acting as scattering centers. Nonetheless, for low doping concentrations (1 doping site per similar to 200 atoms), the quantum conductance for metallic nanotubes is found to be only slightly reduced. The substitutional doping also alters the mechanical strength, leading to a 50% reduction in the elongation upon fracture, while Young's modulus remains approximately unchanged. Overall, the PN- and P-doped nanotubes display promising properties for components in composite materials and, in particular, for fast response and ultra sensitive sensors operating at the molecular level.