Showing papers on "Electronic structure published in 2015"
11 Dec 2015
TL;DR: The Open Quantum Materials Database (OQMD) as discussed by the authors is a high-throughput database consisting of nearly 300,000 density functional theory (DFT) total energy calculations of compounds from the Inorganic Crystal Structure Database (ICSD).
Abstract: The Open Quantum Materials Database (OQMD) is a high-throughput database currently consisting of nearly 300,000 density functional theory (DFT) total energy calculations of compounds from the Inorganic Crystal Structure Database (ICSD) and decorations of commonly occurring crystal structures. To maximise the impact of these data, the entire database is being made available, without restrictions, at www.oqmd.org/download
. In this paper, we outline the structure and contents of the database, and then use it to evaluate the accuracy of the calculations therein by comparing DFT predictions with experimental measurements for the stability of all elemental ground-state structures and 1,670 experimental formation energies of compounds. This represents the largest comparison between DFT and experimental formation energies to date. The apparent mean absolute error between experimental measurements and our calculations is 0.096 eV/atom. In order to estimate how much error to attribute to the DFT calculations, we also examine deviation between different experimental measurements themselves where multiple sources are available, and find a surprisingly large mean absolute error of 0.082 eV/atom. Hence, we suggest that a significant fraction of the error between DFT and experimental formation energies may be attributed to experimental uncertainties. Finally, we evaluate the stability of compounds in the OQMD (including compounds obtained from the ICSD as well as hypothetical structures), which allows us to predict the existence of ~3,200 new compounds that have not been experimentally characterised and uncover trends in material discovery, based on historical data available within the ICSD. Researchers in the USA and Germany introduce a database of over 300,000 calculations detailing the electronic structure and stability of inorganic materials. Chris Wolverton and co-workers from Northwestern University and the Leibniz Institute for Information Infrastructure describe the structure of the Open Quantum Materials Database—a catalog storing information about the electronic properties of a significant fraction of the known crystalline solids determined using density functional theory calculations. Density functional theory is a powerful computational technique that uses quantum mechanics to determine the lowest energy state of the electrons travelling through a lattice of atoms. The researchers verified the accuracy of the calculations by comparing them to experimental results on 1,670 crystals. The database is freely available to scientists, enabling them to design and predict the properties of as yet unrealised materials.
1,235 citations
TL;DR: In this article, a comprehensive first-principles study of the electronic structure of 51 semiconducting monolayer transition-metal dichalcogenides and -oxides in the 2H and 1T hexagonal phases is presented.
Abstract: We present a comprehensive first-principles study of the electronic structure of 51 semiconducting monolayer transition-metal dichalcogenides and -oxides in the 2H and 1T hexagonal phases. The quasiparticle (QP) band structures with spin–orbit coupling are calculated in the G0W0 approximation, and comparison is made with different density functional theory descriptions. Pitfalls related to the convergence of GW calculations for two-dimensional (2D) materials are discussed together with possible solutions. The monolayer band edge positions relative to vacuum are used to estimate the band alignment at various heterostructure interfaces. The sensitivity of the band structures to the in-plane lattice constant is analyzed and rationalized in terms of the electronic structure. Finally, the q-dependent dielectric functions and effective electron and hole masses are obtained from the QP band structure and used as input to a 2D hydrogenic model to estimate exciton binding energies. Throughout the paper we focus on...
892 citations
TL;DR: In this article, it was shown that the non-centrosymmetric compound TaAs is a 3-dimensional topological Weyl semimetal, which is a state of quantum matter with unusual electronic structures that resemble both a 3D graphene and a topological insulator.
Abstract: Experiments show that TaAs is a three-dimensional topological Weyl semimetal. Three-dimensional (3D) topologicalWeyl semimetals (TWSs) represent a state of quantum matter with unusual electronic structures that resemble both a ‘3D graphene’ and a topological insulator. Their electronic structure displays pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming a unique arc-like Fermi surface (FS). Each Weyl point is chiral and contains half the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in momentum space. By performing angle-resolved photoemission spectroscopy on the non-centrosymmetric compound TaAs, here we report its complete band structure, including the unique Fermi-arc FS and linear bulk band dispersion across the Weyl points, in agreement with the theoretical calculations1,2. This discovery not only confirms TaAs as a 3DTWS, but also provides an ideal platform for realizing exotic physical phenomena (for example, negative magnetoresistance, chiral magnetic effects and the quantum anomalous Hall effect) which may also lead to novel future applications.
802 citations
TL;DR: The surface chemistry of porphyrins, phthalocyanines, their metal complexes, and related compounds, with particular focus on chemical reactions at solid/vacuum interfaces, is discussed in this paper.
513 citations
TL;DR: The key aspects of nanophotonic control of the light upconverting nanoparticles through governed design and preparation of hierarchical shells in the core-shell nanostructures are summarized and their emerging applications in the biomedical field, solar energy conversion, as well as security encoding are reviewed.
Abstract: Light upconverting nanostructures employing lanthanide ions constitute an emerging research field recognized with wide ramifications and impact in many areas ranging from healthcare, to energy and, to security. The core–shell design of these nanostructures allows us to deliberately introduce a hierarchy of electronic energy states, thus providing unprecedented opportunities to manipulate the electronic excitation, energy transfer and upconverted emissions. The core–shell morphology also causes the suppression of quenching mechanisms to produce efficient upconversion emission for biophotonic and photonic applications. Using hierarchical architect, whereby each shell layer can be defined to have a specific feature, the electronic structure as well as the physiochemical structure of the upconverting nanomaterials can be tuned to couple other electronic states on the surface such as excitations of organic dye molecules or localized surface plasmons from metallic nanostructures, or to introduce a broad range of imaging or therapeutic modalities into a single conduct. In this review, we summarize the key aspects of nanophotonic control of the light upconverting nanoparticles through governed design and preparation of hierarchical shells in the core–shell nanostructures, and review their emerging applications in the biomedical field, solar energy conversion, as well as security encoding.
461 citations
Journal Article•
TL;DR: In this article, the authors analyzed the electronic structure and optical properties of perovskite solar cells based on CH3NH3PbI3 with the quasiparticle self-consistent GW approximation.
Abstract: The performance of organometallic perovskite solar cells has rapidly surpassed those of both traditional dye-sensitized and organic photovoltaics, e.g. solar cells based on CH3NH3PbI3 have recently reached 18% conversion efficiency. We analyze its electronic structure and optical properties within the quasiparticle self-consistent GW approximation (QSGW ). Quasiparticle self-consistency is essential for an accurate description of the band structure: bandgaps are much larger than what is predicted by the local density approximation (LDA) or GW based on the LDA. Several characteristics combine to make the electronic structure of this material unusual. First, there is a strong driving force for ferroelectricity, as a consequence the polar organic moiety CH3NH3. The moiety is only weakly coupled to the PbI3 cage; thus it can rotate give rise to ferroelectric domains. This in turn will result in internal junctions that may aid separation of photoexcited electron and hole pairs, and may contribute to the current-voltage hysteresis found in perovskite solar cells. Second, spin orbit modifies both valence band and conduction band dispersions in a very unusual manner: both get split at the R point into two extrema nearby. This can be interpreted in terms of a large Dresselhaus term, which vanishes at R but for small excursions about R varies linearly in k. Conduction bands (Pb 6p character) and valence bands (I 5p) are affected differently; moreover the splittings vary with the orientation of the moiety. We will show how the splittings, and their dependence on the orientation of the moiety through the ferroelectric effect, have important consequences for both electronic transport and the optical properties of this material.
418 citations
TL;DR: The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells and bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure.
Abstract: The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm(2) V(-1) s(-1) and diffusion lengths exceeding 1 μm, while mobilities across the mixed Br/I system depend on crystalline phase disorder.
331 citations
TL;DR: In this article, the authors examined mononuclear metal complexes with high magnetic anisotropy and the theoretical approaches used to rationalize their magnetic properties, and developed a set of simple models.
320 citations
TL;DR: If NCs are to be useful within electrical devices, such as photovoltaic (PV) cells, the complex relation between their surface structure and their frontier orbital structure must be better understood.
Abstract: In the 1990s, when quantum confined colloidal semiconductor nanocrystals (NCs, or quantum dots) were first synthesized with narrow size distributions, there was an explosion of effort to harness their bright and narrow luminescence for optoelectronic devices and fluorescence labeling ( 1 ) However, the surfactant ligands that stabilized NCs also influenced their electronic structure and optical properties Encapsulating the NC cores within an insulating inorganic shell reduced the effect of surface structure on charge recombination ( 2 ) and forced the radiative recombination of photoexcited charges These structures greatly increased the photoluminescence quantum yield (PLQY) and enabled their recent use in liquid crystal displays However, PLQYs of core-shell nanocrystals remain sensitive to their surfaces and if NCs are to be useful within electrical devices, such as photovoltaic (PV) cells, the complex relation between their surface structure and their frontier orbital structure must be better understood
294 citations
01 Jan 2015
TL;DR: This work drove a transient charge density wave melting, excited collective vibrations in TbTe3, and observed them through their time-, frequency-, and momentum-dependent influence on the electronic structure and identified the role of the observed collective vibration in the transition.
275 citations
TL;DR: Modeling properties of chemical species and chemical reactions requires usually the quantum-mechanical level of description, and nonlocal embedding operators based on either transferrable pseudopotentials or frozen orbitals obtained from localization procedures have been developed in many groups.
Abstract: Modeling properties of chemical species and chemical reactions requires usually the quantum-mechanical level of description. Methods from the ever-growing toolbox of quantum chemistry1,2 are used for this purpose. Due to unfavorable scaling of quantum chemistry methods, a compromise must be made between the accuracy of the numerical results and the size of the system described at the wave function level. The same strategy can be extended for separating molecular fragments or molecules. Nonlocal embedding operators based on either transferrable pseudopotentials or frozen orbitals obtained from localization procedures have been developed in many groups. The essential feature of all such local potentials is that they comprise a component which takes into account the intermolecular Pauli repulsion.
TL;DR: The results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications.
Abstract: Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations The direct optical band gap of the monolayer 2H-MoS2 increases by 117% from 185 to 208 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure–property relation due to the rich band structure of MoS2 Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures This substantial reversible tunability of the electronic and vibr
TL;DR: In this article, the authors performed quantum Monte Carlo calculations and found that the interlayer interaction in bulk black phosphorus and related few-layer phosphorene is associated with a significant charge redistribution that is incompatible with purely dispersive forces and not captured by density functional theory calculations with different vdW corrected functionals.
Abstract: Sensitive dependence of the electronic structure on the number of layers in few-layer phosphorene raises a question about the true nature of the interlayer interaction in so-called "van der Waals (vdW) solids". We performed quantum Monte Carlo calculations and found that the interlayer interaction in bulk black phosphorus and related few-layer phosphorene is associated with a significant charge redistribution that is incompatible with purely dispersive forces and not captured by density functional theory calculations with different vdW corrected functionals. These findings confirm the necessity of more sophisticated treatment of nonlocal electron correlation in total energy calculations.
TL;DR: In this paper, a self-contained introduction to electronic structure calculations for single molecule magnet properties is provided in conjunction with several contemporary case studies on diverse mononuclear 3d-transition metal complexes.
TL;DR: The controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method is reported, for the first time, to show p-type semiconductor characteristics and high photoresponsivity comparable to exfoliated GaSe nanosheets.
Abstract: Compared with their bulk counterparts, atomically thin two-dimensional (2D) crystals exhibit new physical properties, and have the potential to enable next-generation electronic and optoelectronic devices. However, controlled synthesis of large uniform monolayer and multi-layer 2D crystals is still challenging. Here, we report the controlled synthesis of 2D GaSe crystals on SiO2/Si substrates using a vapor phase deposition method. For the first time, uniform, large (up to ~60 μm in lateral size), single-crystalline, triangular monolayer GaSe crystals were obtained and their structure and orientation were characterized from atomic scale to micrometer scale. The size, density, shape, thickness, and uniformity of the 2D GaSe crystals were shown to be controllable by growth duration, growth region, growth temperature, and argon carrier gas flow rate. The theoretical modeling of the electronic structure and Raman spectroscopy demonstrate a direct-to-indirect bandgap transition and progressive confinement-induced bandgap shifts for 2D GaSe crystals. The 2D GaSe crystals show p-type semiconductor characteristics and high photoresponsivity (~1.7 A/W under white light illumination) comparable to exfoliated GaSe nanosheets. These 2D GaSe crystals are potentially useful for next-generation electronic and optoelectronic devices such as photodetectors and field-effect transistors.
TL;DR: In this paper, it was shown that the alignment of the O 2p valence bands and the unoccupied Co 3d conduction bands improves the conductivity of the La1-xSrxCoO3 perovskite series.
Abstract: The bulk electronic structure, surface composition, conductivity, and electrochemical activity toward the oxygen evolution reaction for the La1–xSrxCoO3 perovskite series (with x = 0, 0.2, 0.4, 0.6, 0.8, 1) are investigated experimentally and theoretically. It is found that Sr substitutions have the effect of straightening the octahedral cage, aligning atoms along the Co–O–Co axis, and increasing the average oxidation state of the Co cations. As a consequence, both the ex situ electronic conductivity as well as the activity toward the oxygen evolution reaction are considerably improved. According to density-functional theory calculations, the alignment of the Co–O–Co bonds and the oxidation of the Co cations enhance the overlap between the occupied O 2p valence bands and the unoccupied Co 3d conduction bands, rationalizing the improvement of the conductivity as a function of the Sr fraction. Additionally, a study of the surface properties as a function of the Sr fraction, carried out by X-ray photoelectro...
TL;DR: In this article, a DFT+U calculation was performed on the electronic structure and catalytic performance of a β-MnO2 catalyst for the oxygen reduction reaction (ORR) with different numbers and extents of OVs.
Abstract: Oxygen vacancies (OVs) are important for changing the geometric and electronic structures as well as the chemical properties of MnO2. In this study, we performed a DFT+U calculation on the electronic structure and catalytic performance of a β-MnO2 catalyst for the oxygen reduction reaction (ORR) with different numbers and extents of OVs. Comparing those results with the experimental XRD analysis, we determined that OVs produce a new crystalline phase of β-MnO2. Changes in the electronic structure (Bader charges, band structure, partial density of states, local density of states, and frontier molecular orbital), proton insertion, and oxygen adsorption in β-MnO2 (110) were investigated as a function of the bulk OVs. The results show that a moderate concentration of bulk OVs reduced the band gap, increased the Fermi and HOMO levels of the MnO2 (or MnOOH), and elongated the O–O bond of the adsorbed O2 and coadsorbed O2 with H. These changes substantially increase the conductivity of MnO2 for the catalysis of ...
TL;DR: This work demonstrates that modulating electronic structures by transition-metal doping is expected to provide effective means to manipulate electronic, optical, chemical, and catalytic properties of thiolated noble metal nanoclusters.
Abstract: With the incorporation of Pd or Pt atoms, thiolated Ag-rich 25-metal-atom nanoclusters were successfully prepared and structurally characterized for the first time. With a composition of [PdAg24(SR)18]2– or [PtAg24(SR)18]2–, the obtained 25-metal-atom nanoclusters have a metal framework structure similar to that of widely investigated Au25(SR)18. In both clusters, a M@Ag12 (M = Pd, Pt) core is capped by six distorted dimeric -RS-Ag-SR-Ag-SR- units. However, the silver-thiolate overlayer gives rise to a geometric chirality at variance to Au25(SR)18. The effect of doping on the electronic structure was studied through measured optical absorption spectra and ab initio analysis. This work demonstrates that modulating electronic structures by transition-metal doping is expected to provide effective means to manipulate electronic, optical, chemical, and catalytic properties of thiolated noble metal nanoclusters.
Journal Article•
TL;DR: In this paper, the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monoline 2H-MoSi2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations were investigated.
Abstract: Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure–property relation due to the rich band structure of MoS2. Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibr...
TL;DR: It is shown that an electric field perpendicular to the layers can induce a semiconductor to metal transition in this family of compounds.
Abstract: We use first-principle calculations to investigate the electronic structure of InSe and In2Se3. The interlayer binding energy is found to be in the same range as for other 2D systems, and the monolayers are found to be dynamically stable, which suggest the possibility to obtain them as isolated layers. The GW approximation including spin-orbit is used to obtain the bandgaps, which are in the range relevant for application in electronics. Also, it is shown that an electric field perpendicular to the layers can induce a semiconductor to metal transition in this family of compounds.
TL;DR: It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one, and all four sheets have ultrahigh carrier mobility and show anisotropy in-plane.
Abstract: Theoretical predictions on the electronic structure and charge carrier mobility in 2D Phosphorus sheets
TL;DR: This work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides to identify those situations where small masses and band-like conduction are more likely to be expected.
Abstract: Open shell transition metal oxides are usually described as Mott or charge transfer insulators, which are often viewed as being disparate from semiconductors. Based on the premise that the presence of a correlated gap and semiconductivity are not mutually exclusive, this work reviews electronic structure calculations on the binary 3d oxides, so to distill trends and design principles for semiconducting transition metal oxides. This class of materials possesses the potential for discovery, design, and development of novel functional semiconducting compounds, e.g. for energy applications. In order to place the 3d orbitals and the sp bands into an integrated picture, band structure calculations should treat both contributions on the same footing and, at the same time, account fully for electron correlation in the 3d shell. Fundamentally, this is a rather daunting task for electronic structure calculations, but quasi-particle energy calculations in GW approximation offer a viable approach for band structure predictions in these materials. Compared to conventional semiconductors, the inherent multivalent nature of transition metal cations is more likely to cause undesirable localization of electron or hole carriers. Therefore, a quantitative prediction of the carrier self-trapping energy is essential for the assessing the semiconducting properties and to determine whether the transport mechanism is a band-like large-polaron conduction or a small-polaron hopping conduction. An overview is given for the binary 3d oxides on how the hybridization between the 3d crystal field symmetries with the O-p orbitals of the ligands affects the effective masses and the likelihood of electron and hole self-trapping, identifying those situations where small masses and band-like conduction are more likely to be expected. The review concludes with an illustration of the implications of the increased electronic complexity of transition metal cations on the defect physics and doping, using as an example the diversity of possible atomic and magnetic configurations of the O vacancy in TiO(2), and the high levels of hole doping in Co(2)ZnO(4) due to a self-doping mechanism that originates from the multivalence of Co.
TL;DR: How valleytronics is possible in these materials by selective interaction of electrons in the different valleys using polarized light is discussed, and for some structures semiconductor-metal transitions could be possible.
Abstract: Transition-metal dichalcogenides TX2 (T = W, Mo; X = S, Se, Te) are layered materials that are available in ultrathin forms such as mono-, bi- and multilayers, which are commonly known as two-dimensional materials. They have an intrinsic band gap in the range of some 500 meV to 2 eV, depending on the composition and number of layers, and giant intrinsic spin–orbit splittings for odd layer numbers, and, in conjunction with their high chemical and mechanical stability, they qualify as candidate materials for two-dimensional flexible electronics and spintronics. The electronic structure of each TX2 material is very sensitive to external factors, in particular towards electric and magnetic fields. A perpendicular electric field reduces the band gap, and for some structures semiconductor–metal transitions could be possible. Moreover, the electric field triggers the spin–orbit splitting for bilayers. A magnetic field applied normal to the layers causes the Hall effect, which in some cases may result in a quantum (spin) Hall effect and thus in magnetic switches. Finally, we discuss how valleytronics is possible in these materials by selective interaction of electrons in the different valleys using polarized light.
TL;DR: The present analysis suggests that, while MB-MD correctly reproduces both the shifts and the shapes of the main spectroscopic features, an improved description of quantum dynamical effects possibly combined with a dissociable water potential may be necessary for a quantitative representation of the OH stretch band.
Abstract: Vibrational spectroscopy is a powerful technique to probe the structure and dynamics of water. However, deriving an unambiguous molecular-level interpretation of the experimental spectral features remains a challenge due to the complexity of the underlying hydrogen-bonding network. In this contribution, we present an integrated theoretical and computational framework (named many-body molecular dynamics or MB-MD) that, by systematically removing uncertainties associated with existing approaches, enables a rigorous modeling of vibrational spectra of water from quantum dynamical simulations. Specifically, we extend approaches used to model the many-body expansion of interaction energies to develop many-body representations of the dipole moment and polarizability of water. The combination of these "first-principles" representations with centroid molecular dynamics simulations enables the simulation of infrared and Raman spectra of liquid water under ambient conditions that, without relying on any ad hoc parameters, are in good agreement with the corresponding experimental results. Importantly, since the many-body energy, dipole, and polarizability surfaces employed in the simulations are derived independently from accurate fits to correlated electronic structure data, MB-MD allows for a systematic analysis of the calculated spectra in terms of both electronic and dynamical contributions. The present analysis suggests that, while MB-MD correctly reproduces both the shifts and the shapes of the main spectroscopic features, an improved description of quantum dynamical effects possibly combined with a dissociable water potential may be necessary for a quantitative representation of the OH stretch band.
TL;DR: The electronic structure of Cd3As2 is investigated by angle-resolved photoemission measurements on the crystal surface and detailed band structure calculations and the topological surface state with a linear dispersion approaching the Fermi level is identified for the first time.
Abstract: The three-dimensional topological semimetals represent a new quantum state of matter. Distinct from the surface state in the topological insulators that exhibits linear dispersion in two-dimensional momentum plane, the three-dimensional semimetals host bulk band dispersions linearly along all directions. In addition to the gapless points in the bulk, the three-dimensional Weyl/Dirac semimetals are also characterized by “topologically protected” surface state with Fermi arcs on their surface. While Cd3As2 is proposed to be a viable candidate of a Dirac semimetal, more investigations are necessary to pin down its nature. In particular, the topological surface state, the hallmark of the three-dimensional semimetal, has not been observed in Cd3As2. Here we report the electronic structure of Cd3As2 investigated by angle-resolved photoemission measurements on the (112) crystal surface and detailed band structure calculations. The measured Fermi surface and band structure show a good agreement with the band structure calculations with two bulk Dirac-like bands approaching the Fermi level and forming Dirac points near the Brillouin zone center. Moreover, the topological surface state with a linear dispersion approaching the Fermi level is identified for the first time. These results provide experimental indications on the nature of topologically non-trivial three-dimensional Dirac cones in Cd3As2.
TL;DR: A procedure to map electronic structure Hamiltonians to 2-body qubit Hamiltonians with a small set of physically realizable couplings with precision requirements on the coupling strengths and a number of ancilla qubits that scale polynomially in the problem size is described.
Abstract: We show how to apply the quantum adiabatic algorithm directly to the quantum computation of molecular properties. We describe a procedure to map electronic structure Hamiltonians to 2-body qubit Hamiltonians with a small set of physically realizable couplings. By combining the Bravyi-Kitaev construction to map fermions to qubits with perturbative gadgets to reduce the Hamiltonian to 2-body, we obtain precision requirements on the coupling strengths and a number of ancilla qubits that scale polynomially in the problem size. Hence our mapping is efficient. The required set of controllable interactions includes only two types of interaction beyond the Ising interactions required to apply the quantum adiabatic algorithm to combinatorial optimization problems. Our mapping may also be of interest to chemists directly as it defines a dictionary from electronic structure to spin Hamiltonians with physical interactions.
TL;DR: Recent developments underpinning the theory of charge pair generation and phenomena are reviewed, focussing on electronic structure calculations, electrostatic models and approaches to excited state dynamics.
Abstract: Efficient charge pair generation is observed in many organic photovoltaic (OPV) heterojunctions, despite nominal electron–hole binding energies which greatly exceed the average thermal energy. Empirically, the efficiency of this process appears to be related to the choice of donor and acceptor materials, the resulting sequence of excited state energy levels and the structure of the interface. In order to establish a suitable physical model for the process, a range of different theoretical studies have addressed the nature and energies of the interfacial states, the energetic profile close to the heterojunction and the dynamics of excited state transitions. In this paper, we review recent developments underpinning the theory of charge pair generation and phenomena, focussing on electronic structure calculations, electrostatic models and approaches to excited state dynamics. We discuss the remaining challenges in achieving a predictive approach to charge generation efficiency.
TL;DR: Large transverse magnetoreistance and field-induced metal-semiconductor-like transition, in NbSb2 single crystal, revealing the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility.
Abstract: The magnetic field response of the transport properties of novel materials and then the large magnetoresistance effects are of broad importance in both science and application. We report large transverse magnetoreistance (the magnetoresistant ratio ~ 1.3 × 105% in 2 K and 9 T field, and 4.3 × 106% in 0.4 K and 32 T field, without saturation) and field-induced metal-semiconductor-like transition, in NbSb2 single crystal. Magnetoresistance is significantly suppressed but the metal-semiconductor-like transition persists when the current is along the ac-plane. The sign reversal of the Hall resistivity and Seebeck coefficient in the field, plus the electronic structure reveal the coexistence of a small number of holes with very high mobility and a large number of electrons with low mobility. The large MR is attributed to the change of the Fermi surface induced by the magnetic field which is related to the Dirac-like point, in addition to orbital MR expected for high mobility metals.
TL;DR: This work uses a solid-state quantum register realized in a nitrogen-vacancy defect in diamond to compute the bond dissociation curve of the minimal basis helium hydride cation, HeH(+), with an energy uncertainty of 10(-14) hartree, which is 10 orders of magnitude below the desired chemical precision.
Abstract: Ab initio computation of molecular properties is one of the most promising applications of quantum computing. While this problem is widely believed to be intractable for classical computers, efficient quantum algorithms exist which have the potential to vastly accelerate research throughput in fields ranging from material science to drug discovery. Using a solid-state quantum register realized in a nitrogen-vacancy (NV) defect in diamond, we compute the bond dissociation curve of the minimal basis helium hydride cation, HeH+. Moreover, we report an energy uncertainty (given our model basis) of the order of 10–14 hartree, which is 10 orders of magnitude below the desired chemical precision. As NV centers in diamond provide a robust and straightforward platform for quantum information processing, our work provides an important step toward a fully scalable solid-state implementation of a quantum chemistry simulator.
TL;DR: This work reveals the physical origin of the Ti(3+) related photo absorption and visible light photocatalytic activity in prototypical TiO2 and also paves the way for the investigation of the electronic structure and photoabsorption of other metal oxides.
Abstract: In reduced TiO2, electronic transitions originating from the Ti3+-induced states in the band gap are known to contribute to the photoabsorption, being in fact responsible for the material’s blue color, but the excited states accessed by these transitions have not been characterized in detail. In this work we investigate the excited state electronic structure of the prototypical rutile TiO2(110) surface using two-photon photoemission spectroscopy (2PPE) and density functional theory (DFT) calculations. Using 2PPE, an excited resonant state derived from Ti3+ species is identified at 2.5 ± 0.2 eV above the Fermi level (EF) on both the reduced and hydroxylated surfaces. DFT calculations reveal that this excited state is closely related to the gap state at ∼1.0 eV below EF, as they both result from the Jahn–Teller induced splitting of the 3d orbitals of Ti3+ ions in reduced TiO2. Localized excitation of Ti3+ ions via 3d → 3d transitions from the gap state to this empty resonant state significantly increases th...