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Showing papers on "Electronic structure published in 2020"


Journal ArticleDOI
TL;DR: CP2K as discussed by the authors is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems, especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations.
Abstract: CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular, and biological systems. It is especially aimed at massively parallel and linear-scaling electronic structure methods and state-of-the-art ab initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post–Hartree–Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.

938 citations


Journal ArticleDOI
TL;DR: This review revisits the main capabilities of CP2K to perform efficient and accurate electronic structure simulations and puts the emphasis on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.
Abstract: CP2K is an open source electronic structure and molecular dynamics software package to perform atomistic simulations of solid-state, liquid, molecular and biological systems. It is especially aimed at massively-parallel and linear-scaling electronic structure methods and state-of-the-art ab-initio molecular dynamics simulations. Excellent performance for electronic structure calculations is achieved using novel algorithms implemented for modern high-performance computing systems. This review revisits the main capabilities of CP2k to perform efficient and accurate electronic structure simulations. The emphasis is put on density functional theory and multiple post-Hartree-Fock methods using the Gaussian and plane wave approach and its augmented all-electron extension.

632 citations


Journal ArticleDOI
15 Sep 2020-Carbon
TL;DR: In this article, the electronic spectrum and optical nonlinearity of the sp-hybridized cyclo[18]carbon with novel topology are studied by means of (time-dependent) density functional theory calculations.

388 citations


Journal ArticleDOI
TL;DR: In this review, a detailed snapshot of current progress in quantum algorithms for ground-state, dynamics, and thermal-state simulation is taken and their strengths and weaknesses for future developments are analyzed.
Abstract: As we begin to reach the limits of classical computing, quantum computing has emerged as a technology that has captured the imagination of the scientific world. While for many years, the ability to execute quantum algorithms was only a theoretical possibility, recent advances in hardware mean that quantum computing devices now exist that can carry out quantum computation on a limited scale. Thus, it is now a real possibility, and of central importance at this time, to assess the potential impact of quantum computers on real problems of interest. One of the earliest and most compelling applications for quantum computers is Feynman's idea of simulating quantum systems with many degrees of freedom. Such systems are found across chemistry, physics, and materials science. The particular way in which quantum computing extends classical computing means that one cannot expect arbitrary simulations to be sped up by a quantum computer, thus one must carefully identify areas where quantum advantage may be achieved. In this review, we briefly describe central problems in chemistry and materials science, in areas of electronic structure, quantum statistical mechanics, and quantum dynamics that are of potential interest for solution on a quantum computer. We then take a detailed snapshot of current progress in quantum algorithms for ground-state, dynamics, and thermal-state simulation and analyze their strengths and weaknesses for future developments.

327 citations


Journal ArticleDOI
TL;DR: A combined experimental and theoretical study clearly identified that low-electronegative B dopant could reform the local electronic configuration and atomic arrangement of bonded Co and adjacent P atoms, enhance the electrons' delocalization capacity of Co atoms for high electrical conductivity, and optimize the free energy of H adsorption and H2 desorption on the active sites for better HER kinetics.
Abstract: Even though transition-metal phosphides (TMPs) have been developed as promising alternatives to Pt catalyst for the hydrogen evolution reaction (HER), further improvement of their performance requires fine regulation of the TMP sites related to their specific electronic structure. Herein, for the first time, boron (B)-modulated electrocatalytic characteristics in CoP anchored on the carbon nanotubes (B-CoP/CNT) with impressive HER activities over a wide pH range are reported. The HER performance surpasses commercial Pt/C in both neutral and alkaline media at large current density (>100 mA cm-2 ). A combined experimental and theoretical study identified that the B dopant could reform the local electronic configuration and atomic arrangement of bonded Co and adjacent P atoms, enhance the electrons' delocalization capacity of Co atoms for high electrical conductivity, and optimize the free energy of H adsorption and H2 desorption on the active sites for better HER kinetics.

192 citations


Journal ArticleDOI
15 Sep 2020-Carbon
TL;DR: In this article, the cyclo[18] carbon has been investigated in terms of its bonding character, electron delocalization, and aromaticity by quantum chemistry calculation and wave function analysis.

173 citations


Journal ArticleDOI
TL;DR: In this paper, the flat bands in twisted bilayer WSe2 are shown near both 0° and 60° twist angles, in agreement with first-principles density functional theory calculations.
Abstract: The crystal structure of a material creates a periodic potential that electrons move through giving rise to its electronic band structure. When two-dimensional materials are stacked, the resulting moire pattern introduces an additional periodicity so that the twist angle between the layers becomes an extra degree of freedom for the resulting heterostructure. As this angle changes, the electronic band structure is modified leading to the possibility of flat bands with localized states and enhanced electronic correlations1–6. In transition metal dichalcogenides, flat bands have been theoretically predicted to occur for long moire wavelengths over a range of twist angles around 0° and 60° (ref. 4) giving much wider versatility than magic-angle twisted bilayer graphene. Here, we show the existence of a flat band in the electronic structure of 3° and 57.5° twisted bilayer WSe2 samples using scanning tunnelling spectroscopy. Our direct spatial mapping of wavefunctions at the flat-band energy show that the localization of the flat bands is different for 3° and 57.5°, in agreement with first-principles density functional theory calculations4. Using scanning tunnelling spectroscopy, the flat bands in twisted bilayer WSe2 are shown near both 0° and 60° twist angles.

171 citations


Journal ArticleDOI
TL;DR: OrbNet is shown to outperform existing methods in terms of learning efficiency and transferability for the prediction of density functional theory results while employing low-cost features that are obtained from semi-empirical electronic structure calculations.
Abstract: We introduce a machine learning method in which energy solutions from the Schrodinger equation are predicted using symmetry adapted atomic orbital features and a graph neural-network architecture. OrbNet is shown to outperform existing methods in terms of learning efficiency and transferability for the prediction of density functional theory results while employing low-cost features that are obtained from semi-empirical electronic structure calculations. For applications to datasets of drug-like molecules, including QM7b-T, QM9, GDB-13-T, DrugBank, and the conformer benchmark dataset of Folmsbee and Hutchison [Int. J. Quantum Chem. (published online) (2020)], OrbNet predicts energies within chemical accuracy of density functional theory at a computational cost that is 1000-fold or more reduced.

156 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a conceptually simple and easy way to automatically identify π orbitals for any kind of systems, which makes subsequent analyses of π electrons straightforward.
Abstract: The characteristic of π electrons has a crucial role in determining various properties of chemical systems, such as reactivity, aromaticity and spectroscopy. There are a large number of methods could be used for investigating π electronic structure, for example, the well-known electron localization function and multicenter bond order. For completely planar systems, the π molecular orbitals can be unambiguously identified and thus studying their π electronic structure is easy. However, for non-planar systems, identification of π orbitals and then analysis of π electrons are often not trivial. In this work, based on localized molecular orbitals (LMOs), we propose a conceptually simple and easy way to automatically identify π orbitals for any kind of systems, which makes subsequent analyses of π electrons straightforward. In addition, we show that the identified π LMOs can also be used to reliably estimate π component of molecular orbitals or other kinds of orbitals. The method proposed in this work has been implemented into our wavefunction analysis code Multiwfn as a key ingredient of standard analysis protocol for π electrons. Application examples given in this article illustrated that this protocol makes analysis of π electronic structure for a wide variety of chemical systems unprecedentedly convenient and reliable.

146 citations


Journal ArticleDOI
TL;DR: The problem of finding the minimum number of fully commuting groups of terms covering the whole Hamiltonian is found to be equivalent to the minimum clique cover problem for a graph representing Hamiltonian terms as vertices and commutativity between them as edges.
Abstract: The Variational Quantum Eigensolver approach to the electronic structure problem on a quantum computer involves measurement of the Hamiltonian expectation value. Formally, quantum mechanics allows ...

132 citations


Journal ArticleDOI
Jinhua Luo1, Zhexing Lin1, Yan Zhao1, Shujuan Jiang1, Shaoqing Song1 
TL;DR: In this article, the sp2-hybridized structure of a hollow-concave carbon nitride (C3N4) was exploited for the sustainable and efficient conversion of solar energy to H2 energy.

Journal ArticleDOI
24 Apr 2020
TL;DR: In this paper, high correlated orbitals coupled with phonons in two-dimensional solids are identified for paramagnetic and optically active boron vacancy in hexagonal Boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal.
Abstract: Highly correlated orbitals coupled with phonons in two-dimension are identified for paramagnetic and optically active boron vacancy in hexagonal boron nitride by first principles methods which are responsible for recently observed optically detected magnetic resonance signal. Here, we report ab initio analysis of the correlated electronic structure of this center by density matrix renormalization group and Kohn-Sham density functional theory methods. By establishing the nature of the bright and dark states as well as the position of the energy levels, we provide a complete description of the magneto-optical properties and corresponding radiative and non-radiative routes which are responsible for the optical spin polarization and spin dependent luminescence of the defect. Our findings pave the way toward advancing the identification and characterization of room temperature quantum bits in two-dimensional solids.

Journal ArticleDOI
TL;DR: In this article, the potential of single transition metal atoms (TM, from Ti to Au) supported on g-C3N4 for the oxygen reduction reaction (ORR) was investigated by first-principles calculations.
Abstract: Herein, the potential of single transition metal atoms (TM, from Ti to Au) supported on g-C3N4 (TM/g-C3N4) for the oxygen reduction reaction (ORR) was investigated by first-principles calculations. It was demonstrated that the TM atoms can remain stable in the cavity of g-C3N4 and interact with the substrate via charge transfer from the TM atoms to g-C3N4. Among all the TM/g-C3N4 samples, Pd/g-C3N4 stands out with a low overpotential of 0.46 V, showing good performance for ORR; thus, it has great potential to replace the noble Pt catalyst. The ORR activity of TM/g-C3N4 is a function of ΔE*OH (an energy descriptor). Furthermore, the d-band center and ICOHP (electronic structure descriptors) can quantitatively describe the variation trend of ΔE*OH in addition to Bader charge analysis (a charge transfer descriptor). Considering the number of d orbital electrons and the electronegativity of TM, φ (an intrinsic descriptor) can be applied to predict and reveal the origin of the ORR activity. A bridge from intrinsic characteristics to electronic structures, to charge transfer, to electronic structures and then to adsorption energy has been established, which is conducive to better reveal the ORR activity origin and provide guidance for designing effective ORR electrocatalysts.

Journal ArticleDOI
TL;DR: With a combination of coherent optical transitions and long spin coherence without dilution refrigeration, the SnV is a promising candidate for feasable and scalable quantum networking applications.
Abstract: Solid-state quantum emitters that couple coherent optical transitions to long-lived spin qubits are essential for quantum networks. Here we report on the spin and optical properties of individual tin-vacancy (SnV) centers in diamond nanostructures. Through cryogenic magneto-optical and spin spectroscopy, we verify the inversion-symmetric electronic structure of the SnV, identify spin-conserving and spin-flipping transitions, characterize transition linewidths, measure electron spin lifetimes, and evaluate the spin dephasing time. We find that the optical transitions are consistent with the radiative lifetime limit even in nanofabricated structures. The spin lifetime is phonon limited with an exponential temperature scaling leading to ${T}_{1}g10\text{ }\text{ }\mathrm{ms}$, and the coherence time, ${T}_{2}^{*}$ reaches the nuclear spin-bath limit upon cooling to 2.9 K. These spin properties exceed those of other inversion-symmetric color centers for which similar values require millikelvin temperatures. With a combination of coherent optical transitions and long spin coherence without dilution refrigeration, the SnV is a promising candidate for feasable and scalable quantum networking applications.

Journal ArticleDOI
01 Feb 2020-Carbon
TL;DR: In this article, the effect of layer thickness, electrical field and strain on the electronic properties of the C 2 N nanosheet was investigated, and it was shown that increasing the thickness of C 2 n can decrease the band gap and induce semiconductor-to-metal transition.

Journal ArticleDOI
TL;DR: A state-of-the-art analysis of accurate energy measurements on a quantum computer for computational catalysis, using improved quantum algorithms with more than an order of magnitude improvement over the best previous algorithms.
Abstract: The quantum computation of electronic energies can break the curse of dimensionality that plagues many-particle quantum mechanics. It is for this reason that a universal quantum computer has the potential to fundamentally change computational chemistry and materials science, areas in which strong electron correlations present severe hurdles for traditional electronic structure methods. Here, we present a state-of-the-art analysis of accurate energy measurements on a quantum computer for computational catalysis, using improved quantum algorithms with more than an order of magnitude improvement over the best previous algorithms. As a prototypical example of local catalytic chemical reactivity we consider the case of a ruthenium catalyst that can bind, activate, and transform carbon dioxide to the high-value chemical methanol. We aim at accurate resource estimates for the quantum computing steps required for assessing the electronic energy of key intermediates and transition states of its catalytic cycle. In particular, we present new quantum algorithms for double-factorized representations of the four-index integrals that can significantly reduce the computational cost over previous algorithms, and we discuss the challenges of increasing active space sizes to accurately deal with dynamical correlations. We address the requirements for future quantum hardware in order to make a universal quantum computer a successful and reliable tool for quantum computing enhanced computational materials science and chemistry, and identify open questions for further research.

Journal ArticleDOI
TL;DR: In this article, singlet and pair q-UCCD approaches combined with orbital optimization have been investigated for the solution of challenging electronic structure problems in quantum chemistry, such as H4, H2O, and N2 molecules, and the one-dimensional periodic Fermi-Hubbard chain.
Abstract: The Coupled Cluster (CC) method is used to compute the electronic correlation energy in atoms and molecules and often leads to highly accurate results. However, due to its single-reference nature, standard CC in its projected form fails to describe quantum states characterized by strong electronic correlations and multi-reference projective methods become necessary. On the other hand, quantum algorithms for the solution of many-electron problems have also emerged recently. The quantum unitary variant of CC (UCC) with singles and doubles (q-UCCSD) is a popular wavefunction Ansatz for the variational quantum eigensolver algorithm. The variational nature of this approach can lead to significant advantages compared to its classical equivalent in the projected form, in particular, for the description of strong electronic correlation. However, due to the large number of gate operations required in q-UCCSD, approximations need to be introduced in order to make this approach implementable in a state-of-the-art quantum computer. In this work, we evaluate several variants of the standard q-UCCSD Ansatz in which only a subset of excitations is included. In particular, we investigate the singlet and pair q-UCCD approaches combined with orbital optimization. We show that these approaches can capture the dissociation/distortion profiles of challenging systems, such as H4, H2O, and N2 molecules, as well as the one-dimensional periodic Fermi-Hubbard chain. These results promote the future use of q-UCC methods for the solution of challenging electronic structure problems in quantum chemistry.

Journal ArticleDOI
TL;DR: Experiments at the interface of quantum optics and chemistry have revealed that strong coupling between light and matter can substantially modify the chemical and physical properties of molecules a... as mentioned in this paper, which can be seen as an example of the relationship between quantum mechanics and chemistry.
Abstract: Experiments at the interface of quantum optics and chemistry have revealed that strong coupling between light and matter can substantially modify the chemical and physical properties of molecules a...

Journal ArticleDOI
TL;DR: In this paper, a minimization of the systems internal energy via density functional theory reveals a distribution of different low-symmetry local motifs, including tilting, rotations, and B-atom displacements.
Abstract: Many common crystal structures can be described by a single (or very few) repeated structural motif (``monomorphous structures'') such as octahedron in cubic halide perovskites. Interestingly, recent accumulated evidence suggests that electronic structure calculations based on such macroscopically averaged monomorphous cubic ($Pm\text{\ensuremath{-}}3m$) halide perovskites obtained from x-ray diffraction, show intriguing deviations from experiment. These include systematically too small band gaps, dielectric constants dominated by the electronic, negative mixing enthalpy of alloys, and significant deviations from the measured pair distribution function. We show here that a minimization of the systems $T=0$ internal energy via density functional theory reveals a distribution of different low-symmetry local motifs, including tilting, rotations, and B-atom displacements (``polymorphous networks''). This is found only if one allows for larger-than-minimal cell size that does not geometrically exclude low symmetry motifs. As the (super) cell size increases, the energy is lowered relative to the monomorphous cell, and stabilizes after \ensuremath{\sim}32 formula units (\ensuremath{\ge}160 atoms) are included. Being a result of nonthermal energy minimization in the internal energy without entropy, this correlated set of displacements must represent the intrinsic geometry preferred by the underlying chemical bonding (lone pair bonding), and as such has a different origin than the normal, dynamic thermal disorder modeled by molecular dynamics. Indeed, the polymorphous network, not the monomorphous ansatz, is the kernel structure from which high temperature thermal agitation develops. The emerging physical picture is that the polymorphous network has an average structure with high symmetry, yet the local structural motifs have low symmetries. We find that, compared with monomorphous counterparts, the polymorphous networks have significantly lower predicted total energies, larger band gaps, and ionic dominated dielectric constants, and agree much more closely with the observed pair distribution functions. An analogous polymorphous situation is found in the paraelectric phase of a few cubic oxide perovskites where local polarization takes the role of local displacements in halide perovskites, and in the paramagnetic phases of a few $3d$ oxides where the local spin configuration takes that role.


Journal ArticleDOI
TL;DR: An extension of neural-network quantum states to model interacting fermionic problems and use neural-networks to perform electronic structure calculations on model diatomic molecules to achieve chemical accuracy.
Abstract: Neural-network quantum states have been successfully used to study a variety of lattice and continuous-space problems. Despite a great deal of general methodological developments, representing fermionic matter is however still early research activity. Here we present an extension of neural-network quantum states to model interacting fermionic problems. Borrowing techniques from quantum simulation, we directly map fermionic degrees of freedom to spin ones, and then use neural-network quantum states to perform electronic structure calculations. For several diatomic molecules in a minimal basis set, we benchmark our approach against widely used coupled cluster methods, as well as many-body variational states. On some test molecules, we systematically improve upon coupled cluster methods and Jastrow wave functions, reaching chemical accuracy or better. Finally, we discuss routes for future developments and improvements of the methods presented. Despite the importance of neural-network quantum states, representing fermionic matter is yet to be fully achieved. Here the authors map fermionic degrees of freedom to spin ones and use neural-networks to perform electronic structure calculations on model diatomic molecules to achieve chemical accuracy.

Journal ArticleDOI
TL;DR: In this article, the authors provide an electronic structure theory that maps long-period transition metal dichalcogenide (TMD) superlattices onto diatomic crystals with cations and anions.
Abstract: Transition metal dichalcogenide (TMD) bilayers have recently emerged as a robust and tunable moir\'e system for studying and designing correlated electron physics. In this Rapid Communication, by combining a large-scale first-principles calculation and continuum model approach, we provide an electronic structure theory that maps long-period TMD heterobilayer superlattices onto diatomic crystals with cations and anions. We find that the interplay between the moir\'e potential and Coulomb interaction leads to filling-dependent charge transfer between different moir\'e superlattice regions. We show that the insulating state at half filling found in recent experiments on $\mathrm{W}{\mathrm{Se}}_{2}/\mathrm{W}{\mathrm{S}}_{2}$ is a charge-transfer insulator rather than a Mott-Hubbard insulator. Our work reveals the richness of simplicity in moir\'e quantum chemistry.

Journal ArticleDOI
15 May 2020
TL;DR: In this paper, a first-principles calculation for the electronic and magnetic structure of undoped parent NdNiO2 is presented, which is consistent with that for observing the resistivity minimum and Hall coefficient drop.
Abstract: The recent discovery of Sr-doped infinite-layer nickelate NdNiO2 offers a new platform for investigating unconventional superconductivity in nickelate-based compounds. Most intriguingly, the resistivity minimum and Hall coefficient drop were identified simultaneously in the experiment, reflecting a novel electronic structure and transport property of NdNiO2. Driven by this pioneering work, we present a first-principles calculation for the electronic and magnetic structure of undoped parent NdNiO2. By taking into account experimentally relevant interaction strength, we found that (π, π, π) antiferromagnetic NdNiO2 is a compensated bad metal with small Fermi pockets. However, due to the small exchange coupling between 3d-electrons of Ni and strong hybridization with 5d-electrons of Nd, the discovered antiferromagnetic ordering is very weak. Crucially, with the decreasing of temperature, there exists a phase transition between good paramagnetic metal and bad AFM metal. The estimated transition temperature is ~70–90 K, which is consistent with that for observing the resistivity minimum and Hall coefficient drop. In this regarding, our results provide a plausible physical interpretation for these significant experimental observations.

Journal ArticleDOI
TL;DR: TeraChem is an electronic structure and ab initio molecular dynamics software package designed from the ground up to leverage graphics processing units (GPUs) to perform large-scale ground and excited state quantum chemistry calculations in the gas and the condensed phase.
Abstract: Developed over the past decade, TeraChem is an electronic structure and ab initio molecular dynamics software package designed from the ground up to leverage graphics processing units (GPUs) to perform large-scale ground and excited state quantum chemistry calculations in the gas and the condensed phase. TeraChem’s speed stems from the reformulation of conventional electronic structure theories in terms of a set of individually optimized high-performance electronic structure operations (e.g., Coulomb and exchange matrix builds, one- and two-particle density matrix builds) and rank-reduction techniques (e.g., tensor hypercontraction). Recent efforts have encapsulated these core operations and provided language-agnostic interfaces. This greatly increases the accessibility and flexibility of TeraChem as a platform to develop new electronic structure methods on GPUs and provides clear optimization targets for emerging parallel computing architectures.

Journal ArticleDOI
TL;DR: This version of KinBot tackles C, H, O and S atom containing species and unimolecular reactions, and automatically characterizes kinetically important stationary points on reactive potential energy surfaces and arranges the results into a form that lends itself easily to master equation calculations.

Journal ArticleDOI
TL;DR: The presence of 6s2 (5s2) lone-pair electrons on the B-site Pb (Sn) in all-inorganic and hybrid halide ABX3 perovskites distinguishes these materials from the familiar tetrahedral semiconductors traditionally employed in optoelectronics.
Abstract: The presence of 6s2 (5s2) lone-pair electrons on the B-site Pb (Sn) in all-inorganic and hybrid halide ABX3 perovskites distinguishes these materials from the familiar tetrahedral semiconductors traditionally employed in optoelectronics and is key to many of their appealing properties. These electrons are stereochemically active, albeit often in a hidden fashion, resulting in unusual and highly anharmonic lattice dynamics that are linked to many of the special optoelectronic properties displayed by this material class. This article describes the connections between this atypical electronic configuration and the electronic structure and lattice dynamics of these compounds. We illustrate how the lone pair leads to favorable bandwidths and band alignments, mobile holes, large ionic dielectric response, large positive thermal expansion, and even possibly defect-tolerant electronic transport. Taken together, the evidence suggests that other high-performing semiconductors may be found among compounds with lone-pair-bearing cations in high symmetry environments and a high degree of connectivity between atoms.

Journal ArticleDOI
TL;DR: The CISS effect results from the coupling between the electron linear momentum and its spin in a chiral system and opens a new avenue into spin-controlled processes in chemistry.
Abstract: ConspectusThe electron’s spin, its intrinsic angular momentum, is a quantum property that plays a critical role in determining the electronic structure of molecules. Despite its importance, it is n...

Journal ArticleDOI
TL;DR: In this paper, a comparative study of the many-body electronic structure and theoretical phase diagram of the isostructural materials CaCuO$2$ and NdNiO$_2$ is presented.
Abstract: The demonstration of superconductivity in nickelate analogues of high $T_c$ cuprates provides new perspectives on the physics of correlated electron materials. The degree to which the nickelate electronic structure is similar to that of cuprates is an important open question. This paper presents results of a comparative study of the many-body electronic structure and theoretical phase diagram of the isostructural materials CaCuO$_2$ and NdNiO$_2$. Important differences include the proximity of the oxygen $2p$ bands to the Fermi level, the bandwidth of the transition metal-derived $3d$ bands, and the presence, in NdNiO$_2$, of both Nd-derived $5d$ states crossing the Fermi level and a van Hove singularity that crosses the Fermi level as the out of plane momentum is varied. The low energy physics of NdNiO$_2$ is found to be that of a single Ni-derived correlated band, with additional accompanying weakly correlated bands of Nd-derived states that dope the Ni-derived band. The effective correlation strength of the Ni-derived $d$-band crossing the Fermi level in NdNiO$_2$ is found to be greater than that of the Cu-derived $d$-band in CaCuO$_2$, but the predicted magnetic transition temperature of NdNiO$_2$ is substantially lower than that of CaCuO$_2$ because of the smaller bandwidth.

Journal ArticleDOI
05 Feb 2020
TL;DR: In this paper, the atomic and electronic structure data of an arsenic (As) layer on Ag(1 1 1) were presented, and low-energy electron diffraction and scanning tunneling microscopy data provided evidence for an ordered layer with a lattice constant of 3.6 A.
Abstract: Group V element analogues of graphene have attracted a lot of attention recently due to their semiconducting band structures and several other interesting properties predicted by theoretical investigations in the literature. In this study, we present atomic and electronic structure data of an arsenic (As) layer on Ag(1 1 1). Low-energy electron diffraction and scanning tunneling microscopy data provide evidence for an ordered layer with a lattice constant of 3.6 A. This value fits with the theoretical range of 3.54-3.64 A for buckled arsenene, which is the structure consistently predicted by various theoretical studies. The electronic structure obtained by angle-resolved photoelectron spectroscopy shows the existence of three 2D electron bands within 4 eV below the Fermi level. The number of bands and the agreement between experimental band dispersions and the theoretical band structure provide further evidence for the formation of monolayer buckled arsenene on Ag(1 1 1). (Less)

Posted Content
TL;DR: In this paper, the authors exploit x-ray absorption spectroscopy (XAS) and resonant inelastic xray scattering (RIXS) to probe the doping dependent electronic structure of the NiO$_2$ planes.
Abstract: The recent discovery of superconductivity in Nd$_{1-x}$Sr$_{x}$NiO$_2$ has drawn significant attention in the field. A key open question regards the evolution of the electronic structure with respect to hole doping. Here, we exploit x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the doping dependent electronic structure of the NiO$_2$ planes. Upon doping, a higher energy feature in Ni $L_3$ edge XAS develops in addition to the main absorption peak. By comparing our data to atomic multiplet calculations including $D_{4h}$ crystal field, the doping induced feature is consistent with a $d^8$ spin singlet state, in which doped holes reside in the $d_{x^2-y^2}$ orbitals, similar to doped single band Hubbard models. This is further supported by orbital excitations observed in RIXS spectra, which soften upon doping, corroborating with Fermi level shift associated with increasing holes in the $d_{x^2-y^2}$ orbital.