Ground State Electronic Properties Research Articles

A study of optical properties and electron energy loss spectra of ZnS by linear response theory

The linear response theory has been applied to study the optical properties and electron energy loss spectra of ZnS. The ground state is built using the Full-Potential Linearized Augmented Plane Wave method. Thereafter, the electronic properties such as band structure and density of states are calculated. Calculations of electron energy loss spectra and optical properties are performed on the top of these ground state electronic properties. The calculations are performed using three exchange–correlation kernels namely, adiabatic local density approximation, long range contribution, and the bootstrap. The random phase approximation is also considered. An approach proposed by us to find the material dependent parameter α is used in long range contribution kernel to capture more accurate optical properties. Three values of α viz 0.78, 1.09, and 1.22 are considered. It is observed that the α = 0.78 gives very good results. This proposed scheme is found to work very well for ZnS also. The effect of local field and electron–hole interaction on the spectra is examined. For example after incorporating local field effect the high frequency dielectric constant ε∞ [i.e. ε1E→0eV ], reduces by 9.19, 12.26, 13.51 and 11.02% for random phase approximation, adiabatic local density approximation, long range contribution and bootstrap kernel respectively. In EELS plasmon peak positions are found using the three kernels and random phase approximation. A good accord with experimental results is noted after incorporating local field effects. It is observed that local field effect causes redshift of prominent peak (i.e. plasmon peak) in electron energy loss spectra by 0.61 eV.

Thermal stability and properties of silicon-germanium nanocrystals

Using first-principles calculations and ensemble theory, we have calculated the ground-state energy and electronic properties of SixGe10−xH16 nanocrystals, and analyzed their stability and properties at finite temperatures. We have determined the numerical correspondence between chemical potential and the proportion of element in SixGe10−xH16. The probability of various structures appearing within SixGe10−xH16 nanocrystals depends on temperature and chemical potential environment. The influence of vibrational free energy, as investigated by theoretical computations, is also summarized. The research results show that vibrational free energy enhances the structure stability by the occupation of Ge atoms and results in a more concentrated distribution of the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital.

Charge-exchange-driven interfacial antiferromagnetic ground state in La0.8Sr0.2MnO3 ultrathin films

The evolution of the magnetic ground state of ultrathin 0–10 unit cells (uc) thick La0.8Sr0.2MnO3 films interfaced to an antiferromagnetic La0.45Sr0.55MnO3/SrTiO3(001) buffer layer was investigated with x-ray photoemission electron microscopy. For 0–3 uc La0.8Sr0.2MnO3, we observe antiferromagnetic domains but no ferromagnetic contrast, showing that nominally ferromagnetic La0.8Sr0.2MnO3 adopts the antiferromagnetic ground state of the buffer layer. For larger thicknesses, ferromagnetic domains emerge, confirming that the additional layers revert to the ferromagnetic ground state. We also observe a drastic increase in the complexity of the domain configuration between 3 and 5 uc, which we attribute to competing magnetic and electronic ground states in the system. We attribute the interfacial modified magnetic ground state to charge sharing at the interface due to the chemical potential mismatch, which leads to hole doping at the La0.8Sr0.2MnO3 interface. The present work sheds light on the impact of charge sharing at the interface of complex oxide materials, in particular on the magnetic and electronic states, and presents a strategy for modulating the electronic ground state properties at metallic interfaces.

DFT Calculations on Defect Induced and Doped ASiNR for Sensing the COPD Breath Biomarker

COPD is a respiratory disease with a high mortality rate worldwide. The major cause of death in COPD patients is due to late diagnosis. Early detection of COPD is crucial for significantly reducing the risk of death but is challenging to attain. A distinguished way to early diagnosis is by using the nanosensor for sensing the COPD breath biomarkers. For the first time, we report an armchair silicene nanoribbon (ASiNR) as a promising sensing material for the diagnosis of hexanal a COPD breath biomarker. In this present study, the density functional theory (DFT) with Grimme D2 corrected approach was incorporated to observe the ground state electronic properties and adsorption mechanism of hexanal on the pristine, defect induced (D) and B, C, and N-doped ASiNR systems. N-ASiNR systems show the highest adsorption energy value among previously reported works due to the presence of strong covalent interaction, and it does not show recovery at room temperature. The B-ASiNR system with higher charge transfer exhibits large work function change with the fastest recovery at room temperature in 1.81 s. Our results confirms B-doped ASiNR system acts as an efficient reusable work function-based sensor for the early diagnosis of COPD at room temperature.

Ground state property calculations of LiHn complexes using IBM Qiskit’s quantum simulator

In this study, the variational quantum eigensolver (VQE) on a quantum simulator is used in calculating ground state electronic structure properties of the LiHn, n = 1–3, complexes including their singly charged ions. Results calculated using classical electronic structure algorithms are also included. We investigate the use of the unitary coupled cluster with singles and doubles (UCCSD) Ansatz using VQE within Qiskit and compare results to full configuration interaction (FCI) calculations. Computed ground state energies, electron affinities, ionization potentials, and dipole moments are considered. We report the first-of-its-kind simulated quantum computing results of selected LiHn species and use the parity orbital to qubit mapping scheme. We find that VQE/UCCSD results are comparable to classical coupled clusters with singles and doubles for all considered systems with respect to FCI. A VQE calculation cost evaluation is included in which we evaluate performance using both Jordan–Wigner and parity orbital to qubit mapping schemes. We also discuss some of the current limitations of utilizing VQE for the study of chemical systems.

Metal–insulator transition and G-type antiferromagnetism in CaNbO[formula omitted] perovskite: Insight from DFT+U study

In this work, we have investigated the ground state electronic and magnetic properties of CaNbO3 perovskite using the density functional theory, along with the Hubbard corrections. The study of structural, electronic, and magnetic properties was carried out using semi-empirical parameters. The structural properties reveal that Nb-O bond lengths are unequal in all directions, and ∠O-Nb-O bond angles are not equal to 90°, which makes NbO6 octahedra distorted. The electronic behavior of the compound, considering the strong correlation effect, shows a metal–insulator transition. The reason for this transition is found to be Jahn–Teller distortion. The stable magnetic state of the compound is obtained to be a G-type antiferromagnetic, using various U values.

Regioselective Synthesis of 2,4- and 2,5-Disubstituted 1,3-Thiazoles from 2-Oxo-2-(amino)ethanedithioates via Base-Catalyzed Cyclization

AbstractFacile and efficient methods are reported for the synthesis of 2,4- and 2,5-disubstituted-1,3-thiazoles by the cyclization of 2-oxo-2-(amino)ethanedithioates with TosMIC and α-haloketones in high yields. Key structures were confirmed based on X-ray crystallographic studies. In addition, investigation of ground state geometry, electronic and molecular structural properties, FMOs, global reactivity descriptors, MEP and NCI analyses were predicted to access the information related to the stability, reactivity, and strength of the interactions present in the molecules by quantum chemical calculations. Further, the potency of derivatives was tested against the SARS-Cov2 receptor (PDB ID: 7mc6) via molecular docking approach with binding scores of –6.0 to –8.4 kcal/mol.

Sampling the Materials Space for Conventional Superconducting Compounds.

A large scale study of conventional superconducting materials using a machine-learning accelerated high-throughput workflow is performed, starting by creating a comprehensive dataset of around 7000 electron-phonon calculations performed with reasonable convergence parameters. This dataset is then used to train a robust machine learning model capable of predicting the electron-phonon and superconducting properties based on structural, compositional, and electronic ground-state properties. Using this machine, the transition temperatures (Tc ) of approximately 200000 metallic compounds are evaluated, all of which are on the convex hull of thermodynamic stability (or close to it) to maximize the probability of synthesizability. Compounds predicted to have Tc values exceeding 5K are further validated using density-functional perturbation theory. As a result, 541 compounds with Tc values surpassing 10K, encompassing a variety of crystal structures and chemical compositions, are identified. This work is complemented with a detailed examination of several interesting materials, including nitrides, hydrides, and intermetallic compounds. Particularly noteworthy is LiMoN2 , which is predicted to be superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38K. LiMoN2 has previously been synthesized in this phase, further heightening its potential for practicalapplications.

Surface functionalization of graphene-like boron arsenide monolayer: a first-principles study

In this work, the effects of hydrogen (H) and oxygen (O) adsorption on the electronic and magnetic properties of graphene-like boron arsenide (BAs) monolayer are investigated using first-principles calculations. Pristine monolayer is a non-magnetic two-dimensional (2D) material, exhibiting direct gap semiconductor character with band gap of 0.75 (1.18) eV as calculated by generalized gradient approximation with Perdew–Burke–Ernzerhof (HSE06) functional. Four high-symmetry adsorption sites are considered, including on-top of B atom (), on-top of As atom (), on-top of hollow site (), and on-top of bridge site (). Using the criterion of adsorption energy, it is found that and sites are favorable adsorption sites for H and O adatom, respectively. The analysis of electronic interactions indicate the charge transfer from host BAs monolayer to both adatoms. H adsorption conducts to the emergence of magnetic semiconductor nature in BAs monolayer with a total magnetic moment of 1.00 . Herein, the magnetism is originated mainly from H adatom and its neighbor As atoms. In contrast, the non-magnetic nature of BAs monolayer is preserved upon absorbing O atoms. In this case, the energy gap exhibits a slight reduction of 4%. Further, the effects of adatom coverage are also analyzed. The presented results suggest an effective modification of ground state electronic properties, as well as induction of new feature-rich properties to make new multifunctional 2D materials from non-magnetic BAs monolayer.

Ground state structural, electronic and magnetic properties of Mg-doped LaMnO[formula omitted] perovskite: GGA+U study

The effect of Mg doping on the ground state structural, electronic and magnetic properties has been investigated by means of GGA+U calculations. The inspection of the structure, magnetic moment data and density plots, show that by substituting La by Mg at the La site at a concentration of 0.25, the compound exhibits a Pbnm orthorhombic structure and a half metallic ferromagnetic behaviour with degenerated Mn-eg states. The corresponding average A-site cation radius 〈rA〉 value does not allow metallic-insulator phase transition in the compound. However, by doping Mg on Mn site with the same proportion, the resulting compound shows a Pbnm orthorhombic structure and a half metallic behaviour with degeneracy lifting in Mn-eg states. Our results obtained for LaMn0.75Mg0.25MnO3 agree more with experimental data than those obtained for La0.75Mg0.25MnO3, suggesting that Mg will prefer to substitute at the Mn site due to their close ionic radii.

A Ground-State Dual-Descriptor Strategy for Screening Efficient Singlet Fission Systems.

Exploration of singlet fission (SF) materials is vital for enhancing the photoelectric conversion efficiency of photovoltaic devices, and the development of an effective screening means is in great demand. In this work, we for the first time propose a promising dual-descriptor strategy to predict the SF energetics (ΔESF) from ground-state electronic properties, the gap (GapHL) and exchange energy (KHL) between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), where GapHL plays a dominant role and KHL acts as a correction. This strategy is statistically verified through exploring the effect of N-doping on the electronic/energetic properties of the N-doped tetracene derivatives and isomers. Several rules of thumb are suggested, and the reliability of this strategy is validated by comparison with experiments. This work proposes a novel strategy for exploring SF chromophores with insights into the SF energetics from ground-state properties and certainly has fundamental interest and generality in exploring efficient SF-capable materials.

Quantum Descriptors for Predicting and Understanding the Structure-Activity Relationships of Michael Acceptor Warheads.

Predictive modeling and understanding of chemical warhead reactivities have the potential to accelerate targeted covalent drug discovery. Recently, the carbanion formation free energies as well as other ground-state electronic properties from density functional theory (DFT) calculations have been proposed as predictors of glutathione reactivities of Michael acceptors; however, no clear consensus exists. By profiling the thiol-Michael reactions of a diverse set of singly- and doubly-activated olefins, including several model warheads related to afatinib, here we reexamined the question of whether low-cost electronic properties can be used as predictors of reaction barriers. The electronic properties related to the carbanion intermediate were found to be strong predictors, e.g., the change in the Cβ charge accompanying carbanion formation. The least expensive reactant-only properties, the electrophilicity index, and the Cβ charge also show strong rank correlations, suggesting their utility as quantum descriptors. A second objective of the work is to clarify the effect of the β-dimethylaminomethyl (DMAM) substitution, which is incorporated in the warheads of several FDA-approved covalent drugs. Our data suggest that the β-DMAM substitution is cationic at neutral pH in solution and promotes acrylamide's intrinsic reactivity by enhancing the charge accumulation at Cα upon carbanion formation. In contrast, the inductive effect of the β-trimethylaminomethyl substitution is diminished due to steric hindrance. Together, these results reconcile the current views of the intrinsic reactivities of acrylamides and contribute to large-scale predictive modeling and an understanding of the structure-activity relationships of Michael acceptors for rational TCI design.

Quantum Many-Body Theory from a Solution of the N-Representability Problem.

Here we present a many-body theory based on a solution of the N-representability problem in which the ground-state two-particle reduced density matrix (2-RDM) is determined directly without the many-particle wave function. We derive an equation that re-expresses physical constraints on higher-order RDMs to generate direct constraints on the 2-RDM, which are required for its derivation from an N-particle density matrix, known as N-representability conditions. The approach produces a complete hierarchy of 2-RDM constraints that do not depend explicitly upon the higher RDMs or the wave function. By using the two-particle part of a unitary decomposition of higher-order constraint matrices, we can solve the energy minimization by semidefinite programming in a form where the low-rank structure of these matrices can be potentially exploited. We illustrate by computing the ground-state electronic energy and properties of the H_{8} ring.

Meta-GGA SCAN Functional in the Prediction of Ground State Properties of Magnetic Materials: Review of the Current State

In this review, we consider state-of-the-art density functional theory (DFT) investigations of strongly correlated systems performed with the meta-generalized gradient approximation (meta-GGA) strongly constrained and appropriately normed (SCAN) functional during the last five years. The study of such systems in the framework of the DFT is complicated because the well-known exchange–correlation functionals of the local density approximation (LDA) and generalized gradient approximation (GGA) families are not designed for strong correlations. The influence of the exchange–correlation effects beyond classical LDA and GGA are considered in view of the prediction of the ground state structural, magnetic, and electronic properties of the magnetic materials, including pure metals, binary compounds, and multicomponent Heusler alloys. The advantages of SCAN and points to be enhanced are discussed in this review with the aim of reflecting the modern state of computational materials science.

Neutral, Heteroleptic [Cu(I)(PPh3 )2 (4H-imidazolato)] Complexes: Ligand Exchange Reactivity, Redox Properties, Excited-State Dynamics.

Cu(I) 4H-imidazolate complexes are rare examples of Cu(I) complexes with chelating anionic ligands and are potent photosensitizers with unique absorption and photoredox properties. In this contribution, five novel heteroleptic Cu(I) complexes with monodentate triphenylphosphine co-ligands are investigated. As a consequence of the anionic 4H-imidazolate ligand and in contrast to comparable complexes with neutral ligands, these complexes are more stable than their homoleptic bis(4H-imidazolato)Cu(I) congeners. Here, the ligand exchange reactivity was studied by 31 P-,19 F-, and variable temperature NMR and the ground state structural and electronic properties by X-ray diffraction, absorption spectroscopy, and cyclic voltammetry. The excited-state dynamics were investigated by femto- and nanosecond transient absorption spectroscopy. The observed differences, with respect to chelating bisphosphine bearing congeners, are often due to the increased geometric flexibility of the triphenylphosphines. These observations render the investigated complexes interesting candidates for photo(redox)reactions not accessible with chelating bisphosphine ligands.

Covalent post-assembly modification of π-conjugated supramolecular polymers delivers structurally robust light-harvesting nanoscale objects.

A two-component stapling strategy is used to covalently tether a new class of water-soluble supramolecular polymers built from bay-functionalized perylene bisimide (PBI) units. By leveraging a novel combined strategy where excitonic coupling and fluorescence data are exploited as spectroscopic reporters, structural design principles are established to form light-harvesting superstructures whose ground-state electronic properties are not sensitive to solvation environments. Moreover, we interrogate the structural properties of stapled superstructures by capitalizing on the drastic changes in fluorescence quantum yields against parent supramolecular assemblies. In essence, our work shows that the combination of excitonic coupling measurements and photoluminescence experiments delineates a more accurate understanding of the design principles required to limit the degree of structural defects and magnify short- and long-range electronic couplings between redox-active units in this new class of solvated nanoscale objects. These results highlight that the fragile conformation of non-covalent assemblies, which are regulated by weak secondary interactions, can be preserved by post-assembly modification of preformed supramolecular polymers. These synthetic and spectroscopic principles can in turn be codified as experimental handles to parameterize the optoelectronic properties of light-harvesting nanoscale objects.

The nature of the electronic ground state of M2C (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) MXenes.

A systematic computational study is presented aimed at accurately describing the electronic ground state nature and properties of M2C (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) MXenes. Electronic band structure calculations in the framework of density functional theory (DFT), carried out with different types of basis sets and employing the generalized gradient approach (GGA) and hybrid functionals, provide strong evidence that Ti2C, Zr2C, Hf2C, and Cr2C MXenes exhibit an open-shell conducting ground state with localized spins on the metal atoms, while V2C, Nb2C, Mo2C, Ta2C, and W2C MXenes exhibit a diamagnetic conducting ground state. For Ti2C, Zr2C, Hf2C, and Cr2C, the analysis of the low-lying spin polarized solutions with different spin orderings indicates that their ground states are antiferromagnetic (AFM), consisting of two ferromagnetic (FM) metal layers coupled antiferromagnetically. For the diamagnetic MXenes, the converged spin polarized solutions are significantly less stable than the closed shell solution except for the case of V2C and Mo2C where those excited open shell solutions can be thermally accessible (less than 300 meV per formula unit). The analysis of charge and spin density distributions of the ground state of the MXenes reveals that, in all cases, the metal atoms have a net charge close to +1 e and C atoms close to -2 e. In the case of diamagnetic MXenes, the electronic structure of V2C, Nb2C, and Ta2C is consistent with metal atoms exhibiting a closed-shell s2d2 configuration whereas for Mo2C, and W2C is consistent with a low-spin s1d4 configuration although the FM solution is close in energy for V2C and Mo2C suggesting that they may play a role in their chemistry at high temperature. For the open shell MXenes, the spin density primarily located at the metal atoms showing one unpaired electron per Ti+, Zr+, and Hf+ magnetic center, consistent with s2d1 configuration of the metal atom, and of ∼3.5 unpaired electrons per Cr+ magnetic center interpreted as a mixture of s2d3 and high-spin s1d4 configuration. Finally, the analysis of the density of states reveals the metallic character of all these bare MXenes, irrespective of the nature of the ground state, with significant covalent contributions for Mo2C and W2C.

Impact of organic–inorganic wavefunction delocalization on the electronic and optical properties of one-dimensional hybrid perovskites

This work investigates the impact of electronic couplings between the organic and inorganic components of one-dimensional hybrid perovskites on their ground-state and excited-state electronic properties and optical properties.

Structural, optoelectronic and thermal response of new stable MgBe2X2 (X = As, P) Zintl phases: First-principles calculation

Highly-accurate computational predictions of suitable thermoelectric materials have sparked interest in discovering new Zintl phases. We report a detailed first-principles study to investigate the ground-state structural, electronic, optical and thermoelectric properties of MgBe2X2 (X = As, P) Zintl phases. Both compounds' optimized energy-volume curves, negative formation energies and phonon dispersion curves confirm their stability. A semiconductor nature is observed with bandgap values of 1.04 eV and 1.20 eV for MgBe2As2 and MgBe2P2, respectively. The optical response of the studied phases shows their potential to use in optoelectronic devices. Semi-classical Boltzmann theory is implemented through BoltzTraP code to calculate the thermal response. High Seebeck values are achieved at room temperature as well as at high temperatures. The power factor also shows an increase with the temperature increase. Furthermore, the figure of merit (ZT) shows good value of 0.74 for MgBe2As2 and 0.75 for MgBe2P2. A good optical and thermoelectric response of the studied phases opens the opportunity to use them in optoelectronic and thermoelectric applications.

Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator

In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silvaet al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase.