Electronic Charge Density Research Articles

Suppression of the superconducting phase in new structures of elemental sulfur at terapascal pressures

We perform a computational structure search and study the phase diagram of elemental sulfur up to 100 TPa from first-principles using ab initio random structure searching (airss), discovering six new phases with the transition sequence $\text{bcc}\ensuremath{\rightarrow}I{4}_{1}/acd\ensuremath{\rightarrow}cI16\ensuremath{\rightarrow}\ensuremath{\alpha}\text{-U}\ensuremath{\rightarrow}\text{hcp}\ensuremath{\rightarrow}A15\ensuremath{\rightarrow}\text{bcc}$. The electronic properties and charge density distributions of the new phases are extensively studied. Remarkably, upon transition to the $I{4}_{1}/acd$ phase at 1.24 TPa, the superconducting critical temperature of sulfur abruptly drops from 12 K to just 0.4 K, and above 5 TPa, we find the critical temperature to be zero up to at least 100 TPa. We show that this sudden suppression of superconductivity is coincident with the formation of a sequence of electride phases, which feature significantly reduced electron-phonon coupling and substantial charge localization. Despite ceasing to be a superconductor, sulfur remains metallic up to at least 100 TPa.

Mixed Ionic-Electronic Conduction, a Multifunctional Property in Organic Conductors.

Organic mixed ionic-electronic conductors (OMIECs) have gained recent interest and rapid development due to their versatility in diverse applications ranging from sensing, actuation and computation to energy harvesting/storage, and information transfer. Their multifunctional properties arise from their ability to simultaneously participate in redox reactions as well as modulation of ionic and electronic charge density throughout the bulk of the material. Most importantly, the ability to access charge states with deep modulation through a large extent of its density of states and physical volume of the material enables OMIEC-based devices to display exciting new characteristics and opens up new degrees of freedom in device design. Leveraging the infinite possibilities of the organic synthetic toolbox, this perspective highlights several chemical and structural design approaches to modify OMIECs' properties important in device applications such as electronic and ionic conductivity, color, modulus, etc. Additionally, the ability for OMIECs to respond to external stimuli and transduce signals to myriad types of outputs has accelerated their development in smart systems. This perspective further illustrates how various stimuli such as electrical, chemical, and optical inputs fundamentally change OMIECs' properties dynamically and how these changes can be utilized in device applications.

The chirality of isotopomers of glycine compared using next‐generationQTAIM

AbstractThe effect of a deuterium (D) or tritium (T) isotope bonded to the alpha carbon of glycine is determined without the need to apply external forces, for example, electric fields or using normal mode analysis. Isotopic effects were accounted for using the mass‐dependent diagonal Born‐Oppenheimer energy correction (DBOC) at the CCSD level of theory. We calculated the stress tensor trajectories of the dominant C‐N bond within next generation quantum theory of atoms in molecules (NG‐QTAIM). S‐character chirality was discovered using the stress tensor trajectories, instead of the Cahn–Ingold–Prelog (CIP) rules, for ordinary glycine. The S‐character chirality was preserved after the substitution of the H on the alpha carbon for a D isotope but transformed to R‐character chirality after replacement with the T isotope. This reversal of the chirality depending on the presence of a single D or T isotope bound to the alpha carbon adds to the debate on the nature of the extraterrestrial origins of chirality in simple amino acids. We demonstrate that NG‐QTAIM is a promising tool for understanding isotopic induced electronic charge density changes, useful in analysis of infrared (IR) or circular dichroism (CD) spectra explaining changes in mode couplings and bands intensities or sign.

Opto-electronic, thermodynamic and charge carriers transport properties of Ta2FeNiSn2 and Nb2FeNiSn2 double half-Heusler alloys

A computational research study of the structural, electronic, and optical characteristics of double half-Heusler alloys Ta2FeNiSn2 and Nb2FeNiSn2 is presented by performing ab initio calculations. The density functional theory framework employs the full-potential linearized augmented plane wave method to solve Kohn–Sham equation as implemented in the Wien2k code. The exchange-correlation potential is processed by using the local density approximation and the generalized gradient approximation–Perdew, Burke, and Ernzerhof approximations to calculate the total energy and other physical properties. The obtained results showed that both alloys possess high cohesive energies, where Nb2FeNiSn2 (7.213 eV atom−1) is more consistent than Ta2FeNiSn2 (6.249 eV atom−1), these remarkable results support the structural stability for both alloys. Also, the thermodynamic stability of both compounds was confirmed through calculating the formation energy as the obtained results were close to the results obtained in as well as given the Open Quantum Materials Database. Electronic characteristics and chemical bonding are illustrated and discussed by computing the electron charge density, density of states, and band structure. Both alloys show semiconductor behavior with (∼0.5 eV) indirect energy bandgap. Also, we have calculated and analyzed the complex dielectric function, absorption coefficient, as well as, reflectivity spectra for both compounds. The semi local Boltzmann transport theory has been employed to treat temperature effect on thermoelectric properties of Ta2FeNiSn2 and Nb2FeNiSn2 compounds where the obtained results appears that both compounds have high coefficient at the normal condition, and they also have a good power factor at the Fermi level, which emphasizes that the thermoelectric efficiency of the two compounds is good and does not require doping. Also, depending on quasi-harmonic model was used for estimating the heat capacity, the lattice thermal conductivity, the thermal expansion and the Debye temperature under the pressure effects.

First-principles investigation of equilibrium phase, mechanical and thermodynamic properties of the Nowotny TM5Si3C ternary phase

Although the TM-Si-C ternary compounds are potential high-temperature ceramics, the equilibrium phase, mechanical and thermodynamic properties of Nowotny phase (NP) are still unclear. Here, the structural stability, mechanical and thermodynamic properties of the TM5Si3C Nowotny phase (NP) are studied by the first-principles calcualtions. Four TM5Si3C ternary phases (TM = Mo, Nb, W and Ta) are considered. It is found that the equilibrium structure of the Nowotny phase (NP) is a TM5Si3C. In particular, the Mo5Si3C, Nb5Si3C, W5Si3C and Ta5Si3C are firstly predicted. Nb5Si3C has better thermodynamic stability in comparison to the other TM5Si3C. Furthermore, the calculated elastic properties show that four TM5Si3C not only exhibit similar strength in comparison to the corresponding TM5Si3 and TMSi2, but also show better ductility compared to the corresponding TM-Si binary silicides. The nature of mechanical properties of TM5Si3C is revealed by the electronic structure and difference charge density. In addition, it is further found that four TM5Si3C have high melting points and excellent thermodynamic stability. Naturally, the better thermodynamic properties of TM5Si3C is related to the vibration of C atom in a system.

Theoretical study on Xe⋯N non-covalent interactions: Three hybridization N with XeO3 and XeOF2

The interactions of complexes of XeOF2 and XeO3 with a series of different hybridization N-containing donors are studied by means of DFT and MP2 calculations. The aerogen bonding interaction energies range from 6.5 kcal/mol to 19.9 kcal/mol between XeO3 or XeOF2 and typical N-containing donors. The sequence of interaction for N-containing hybridization is sp3>sp2>sp, and XeO3 is higher than XeOF2. For some donors of sp2 and sp3 hybridization, the steric effect plays a minor role in the interaction with the evidence of reduced density gradient plots. The dominant stable part is the electrostatic interaction. In complex of XeO3, the weight of polarization is larger than dispersion, while the situation is opposite for XeOF2 complexes. Except for the sum of the maximum value of molecular electrostatic potential on Xe atom and minimum value of molecular electrostatic potential on N atom, the otherfive interaction parameters including the potential energy density at bond critical point, the equilibrium distances, interaction energies with the basis set superposition error correction, localized molecular orbital energy decomposition analysis interaction energies, and the electron charge density, show great linear correlation coefficients with each other.

Compton profile and charge density reconstruction by the maximum entropy method

The aim of this work is to propose a theoretical procedure to determine the electron momentum density and Compton profile of valence electrons in solids. The procedure consists in a hybrid methodology that combines the maximum entropy method and Dirac-Hartree–Fock formalism, which allows including exchange and correlation effects on valence electrons for distances near the atomic nucleus and that are approximated using the Breit-Wigner distribution function. This technique can be applied for a wide range of crystalline solids. The results and comparisons reported here are for: lithium, beryllium, aluminum, silicon and copper. The application of the model only requires prior knowledge of the Fermi momentum values. In addition, a reconstruction of the valence electron charge density distribution via simple expression of the Compton profile is derived.

Optoelectronic and photovoltaic properties of Cs 2 AgBiX 6 (X = Br, Cl, or I) halide double perovskite for solar cells: Insight from density functional theory

In this study, the electronic structure, optical, and electrical properties of double perovskite Cs2AgBiX6 (X = Br, Cl, and I) were investigated through the density functional theory within the Tran–Blaha modified Becker–Johnson approach. The optoelectronic properties such as the bandgap energy, density of states, charge density, and dielectric function are discussed. The physical parameters including the quantum efficiency, Voc, Jsc, were estimated for industrial photovoltaics (PV). Based on the optimized structure, it was found that the bandgap values are 1.12, 2.04, and 2.81 eV for Cs2AgBiI6, Cs2AgBiBr6, and Cs2AgBiCl6 respectively. Meanwhile, the electronic charge density predicts that the bounds between Cs and Br/I/Cl are covalent. Quantum efficiency shows high evolution, a very high spectrum of absorption coefficients is observed around the visible range, which proves the use of such double perovskite compound in the PV device.

Preparation, electronic structure and optical properties of Na2GeSe3 crystals

From the first principles, in the framework of the density functional theory in LDA and LDA+U approximations, the band structure, total and partial densities of electronic states, spatial distribution of the electron charge density, also the optical functions: dielectric constant, refractive and absorption indices, reflection and absorption coefficients of Na2GeSе3 crystal have been calculated. According to the calculation results, Na2GeSе3 is a direct-gap crystal with the top of valence band and the bottom of conduction band at the point Г of Brillouin zone. The calculated band gap is Egd = 1.7 eV LDA and Egd = 2.6 eV in the LDA+U approximations. Based on the data of total and partial densities of electronic states, contributions of atomic orbitals to the crystalline ones have been determined. Also, the data of chemical bond formation in the crystals under discussion have been obtained.

An insight into structural, electronic and optical characteristics of Mo1-xMxO3 (M = Zr, Y, ZrY) for the formation of conducting filaments in optoelectronic memory devices: A first principles study

In the present work, we have theoretically investigated the structural, electronic and optical characteristics of Mo1−xMxO3 (M = Zr, Y, co-doped (ZrY)) for Optoelectronic Resistive Random-Access Memory (ORRAM) devices and associated applications. Density functional theory within Heyd-Scuseria-Ernzerhof (HSE06) functional has been employed to better estimate optoelectronic parameters. The structural outcomes, findings of the energy band structure, spin resolved total density of states (TDOS), three dimensional iso-surface electron charge density, electron localization function and Bader charge analysis unveil thatMo1−x(ZrY)xO3 is comparatively more suitable composite with enhanced charge conductance for ORRAM devices. The partial density of states (PDOS) and Bader charge analysis results reveals that noticeable orbital contribution of the constituent atoms mainly in increasing conductivity through hybridization. Formation energy and phonon calculations confirmed that studied structures are stable. The photo absorption behavior shows that Mo1−x(ZrY)xO3 can absorb a broad electromagnetic radiations wavelength range from ultraviolet (UV) to infrared (IR) coherent with the charge conduction property which has been found a most fitted candidate for ORRAM and associated applications.

Large scale dataset of real space electronic charge density of cubic inorganic materials from density functional theory (DFT) calculations

Driven by the big data science, material informatics has attracted enormous research interests recently along with many recognized achievements. To acquire knowledge of materials by previous experience, both feature descriptors and databases are essential for training machine learning (ML) models with high accuracy. In this regard, the electronic charge density ρ(r), which in principle determines the properties of materials at their ground state, can be considered as one of the most appropriate descriptors. However, the systematic electronic charge density ρ(r) database of inorganic materials is still in its infancy due to the difficulties in collecting raw data in experiment and the expensive first-principles based computational cost in theory. Herein, a real space electronic charge density ρ(r) database of 17,418 cubic inorganic materials is constructed by performing high-throughput density functional theory calculations. The displayed ρ(r) patterns show good agreements with those reported in previous studies, which validates our computations. Further statistical analysis reveals that it possesses abundant and diverse data, which could accelerate ρ(r) related machine learning studies. Moreover, the electronic charge density database will also assists chemical bonding identifications and promotes new crystal discovery in experiments.

Effect of Ca2+ doping on the electronic charge density and magnetic properties of ZnFe2O4 spinel ferrites

Effect of Ca2+ doping on the electronic charge density and magnetic properties of ZnFe2O4 spinel ferrites

Ab-initio study of structural stability, electronic and optical properties of X2GeSe (X = P and Sb) monolayers

This paper investigated the structural stability, electronic and optical properties of X2GeSe (X = P and Sb) monolayers in a hexagonal structure. The calculations are based on the density functional theory using the plane wave method in the Quantum-Espresso computational package for local density approximation (LDA) and the generalized gradient approximation (GGA). The results of phononic calculations indicate that P2GeSe and Sb2GeSe monolayers are dynamically stable in LDA and GGA approximations. The electronic section of X2GeSe (X = P and Sb) monolayers showed that both compounds are semiconductors. The P2GeSe and Sb2GeSe monolayers in the LDA approximation exhibit a direct bandgap at the Γ point with a quantity of 0.88 and 0.84 eV, respectively. Also, P2GeSe and Sb2GeSe monolayers have an indirect bandgap in the GGA approximation in the Г−K path whit amount of 1.07 and 1.02 eV, respectively. For X2GeSe monolayers (X = P and Sb), the optical gaps calculated from the absorption spectrum confirm the electronic bandgap results. The optical calculations showed that the static dielectric constant ε1(0) decreases in the x and z directions but increases in the y-direction with increasing constant atomic radius from P to Sb atom. According to the results, in both LDA and GGA approximations, the maximum reflections of the P2GeSe monolayer are in the ultraviolet domain of the electromagnetic spectrum and for the Sb2GeSe monolayer, the maximum of reflections occurs in the infrared domain. This result makes the studied monolayers a potential candidate for use in optoelectronic devices as a reflector layer of the electromagnetic beam. The calculated of the energy loss spectrum L(ω) diagram shows that the significant collective excitations of the electron charge density in the crystal, which is considered as the plasmonic peak, are in the y-direction. The values of the static refractive index n0, obtained from the squares of the real part of the dielectric function at zero energy, n0=ε1(0), are very close to that of the refractive index diagram at zero energy. For every examined monolayer, the static refractive index in the y-direction is larger than other x and z directions in both LDA and GGA approximations. Examination of the optical properties of the X2GeSe (X = P and Sb) monolayers in different x, y, and z-directions explains the anisotropy of the studied structures.

A theoretical study of HCN adsorption and width effect on co-doped armchair graphene nanoribbon

Hydrogen cyanide (HCN) is one of the hazardous gas and requires sensitive detection material. In the present work stable structures, adsorption analysis, charge transfer and electronic properties of defective, pristine, Phosphorus doped, Boron doped and Boron Phosphorus co-doped ArGNRs are studied using first principles calculations combined with Density functional theory (DFT). In two models of ArGNRs with N = 6 and N = 8 atoms along width, it is observed that pristine ArGNR is not a good sensing material for HCN molecule however, on introducing defects and dopants its sensitivity drastically increases and results in chemisorption for all models of ArGNRs. Different doping site optimizations for all models of ArGNR are observed which reveal that defective, Phosphorous doped, Boron-Phosphorus co-doped ArGNR with width N = 6 shows higher negative value of adsorption energy with adsorption energy values are −5.81 eV, −1.27 eV and −1.06 eV. Band nature predicts that for BP-ArGNR with N = 6 shows large reduction as compared to co-doped system of N = 8 model system. A remarkable charge transfer occurs between the HCN molecule and BP-ArGNR as proved by the electronic charge densities. DOS analysis predicts that the defective, phosphorus doped and boron-phosphorus co-doped ArGNRs are good sensing materials with intense peaks after adsorption of cyanide molecule as compared to pristine ArGNR for N = 6 model system. This implies that defective, Phosphorus and B, P co-doped ArGNR with N = 6 has high sensitivity to cyanide molecule as compared to N = 8 model system. Results of our simulated work are not only helpful to evaluate sensing mechanism but also provide a potential sensor material detection of HCN.

Cs2AgBiBr6 as a mixed anion perovskites for photovoltaic applications: A first-principle study

Ab initio calculations were performed for cubic Fm-3 m (225) and tetragonal (I4/m) phases for Cs2AgBiBr6(CaB2). We used the Vienna Ab Initio Simulation Package (VASP) to calculate the ground state properties using two different exchange-correlation functionals, namely the Generalized gradient approximation method (GGA) and the screened hybrid functional as proposed byHeyd,Scuseria, andErnzerhof (HSE06) method. Tetragonal Cs2AgBiBr6 phase was stabilized in the tetragonal phase. The bandgap (Eg) was calculated using HSE06 for the polymorphs optimized at the PBE level and it is found that they belong to the indirect bandgap. The calculated bandgap for cubic and tetragonal phases in HSE06 for Cs2AgBiBr6 were 1.97 eV, and 2.4 eV, respectively. The character of chemical bonding in CaB2 is discussed based on electronic structures, charge density, charge transfer, and bond overlap population analyses.

Tailoring activation of CoNiO nanoparticles/porous carbon nanofibers by atomic doping for high performance supercapacitors.

Metal-organic framework (MOF) materials are rich in active sites and have a high specific surface area, which make them potential electrode materials. In this work, a simple immersion method combined with a carbonization treatment process is applied to prepare MOF derived composite materials (CoNiO/PCNFs). Among them, cobalt-based MOFs (Co-MOFs) are selected as the precursor and doped with Ni atoms, and the ratio of Co and Ni is tailored to acquire a high-performance electrode. The electrochemical results show that when the ratio of Co to Ni is 2 : 2, the prepared CoNiO/PCNFs-2 electrode has high capacitance (912.4 F g-1 at 1 A g-1) and superior rate capability (retention is above 50% at 100 A g-1). Additionally, it is highly stable at 20 A g-1 (nearly no degradation after 6000 cycles). Density Functional Theory (DFT) calculations indicate that the Ni doping models present lower formation energy and better -OH group adsorption properties. Moreover, the density of electronic state (DOS) and differential charge density distribution demonstrate that Ni doping effectively enhances the charge transport during the charging and discharging processes, which is beneficial to enhance the energy storage of the electrode materials. In conclusion, this work presents a strategy to design MOF-derived composite electrodes. The experimental tests and theoretical calculations explore the energy storage process and prove that the CoNiO/PCNF electrode materials have great potential for applications.

Synthesis, crystal structure and in silico studies of novel 2,4-dimethoxy-tetrahydropyrimido[4,5-b]quinolin-6(7H)-ones.

Herein, acetic acid mediated multicomponent synthesis of novel 2,4-dimethoxy-tetrahydropyrimido[4,5-b]quinolin-6(7H)-one (2,4-dimethoxy-THPQs) was reported. Single-crystal XRD analysis of four newly developed crystals of 2,4-dimethoxy-THPQs and their DFT study were also reported. The structure of all molecules was optimized using DFT B3LYP/6-31G(d) level and compared with the corresponding single-crystal XRD data. As a result, the theoretical and experimental geometrical parameters (bond lengths and bond angles) were found to be in good agreement. Frontier molecular orbital (FMO) and molecule electrostatic potential (MEP) analyses were used to investigate the physicochemical properties and relative reactivity of 2,4-dimethoxy-THPQs. The formation of strong C–H⋯O and N–H⋯O interaction was investigated by Hirshfeld analysis. Furthermore, electronic charge density concentration in 2,4-dimethoxy-THPQs was analysed by the Mulliken atomic charges which helps to predict the ability of 2,4-dimethoxy-THPQs to bind in the receptor. The molecular docking of the crystal structure of 2,4-dimethoxy-THPQs in the main protease (Mpro) of SARS-CoV-2 suggested that all four 2,4-dimethoxy-THPQs efficiently docked in Mpro. Furthermore, 2,4-dimethoxy-THPQs with a 3-chloro substitution in the phenyl ring have the highest binding affinity because of the additional formation of halogen bonds and highest dipole moment.

Structural and electronic properties of β-MnO2 nanoclusters

Pyrolusite (β-MnO2) was investigated for potential use in energy storage devices due to its promising properties for cathode materials in rechargeable lithium-ion batteries. A combination of evolutionary algorithm search techniques and density functional theory techniques were used to determine the structural stabilities of the β-MnO2 nanoclusters on the energy landscape. However, pyrolusite suffers from some structural defects and impurities that hinder its optimal use. The predicted order of stability for the MnO2 nanoclusters correlates with isostructural TiO2. There is an improvement in the stability and electrical conductivity of the nanoclusters as compared to their β-MnO2 bulk counterparts. The cobalt doped nanoclusters showed a preference toward circular compact bonding patterns. The band-gap energy revealed that the nanoclusters have a metallic characteristic behaviour with narrow band gap energies, indicating their good conductive properties. Cobalt doping was shown to improve the structural properties of the nanoclusters based on the decreased bond lengths and more spherical bond angles. Moreover, it also succeeded in improving the conductivity of the nanoclusters based on the reduced Mulliken and Hirshfeld partial charges. The electronic charge density differences of the cobalt doped β-MnO2 nanoclusters displayed a prevalence of the weaker ionic bonding instead of the preferred stronger covalent bonding. This shows the limited effectiveness of cobalt as a dopant.

DFT insights into half metallic ferromagnetism of new cubic PerovskiteVYO3 for spintronics application

The electronic structure, magnetic, optical, thermodynamic and thermoelectric properties of Vanadium-based perovskite VYO3 system are systematically investigated via first-principle computations. FP-LAPW method within PBE-GGA and LSDA, based on the density functional theory (DFT), executed in the WIEN2k-19.1 package is used for the computations. To improve the calculations of the electronic structure as well as magnetic characteristics, the Trans-Blaha modified Becke-Johnson (TB-mBJ) exchange potential is used, which can precisely calculate the energy gap of solids. The computed electronic structure reveals the half-metallic ferromagnetic nature for the investigated compound with total magnetic moment of 2.00008μB. The ferromagnetic phase of VYO3 is energetically more stable with negative cohesive energy, according to our findings. This agrees well with the available similar experimental as well as theoretical calculations. The estimated magnetic moments in VYO3 originate especially from the V-3d state electrons. A semiconductor gap (2.19 eV) has been obtained in minority spin channel while in majority spin channel, the metallic character is dominating, and therefore VYO3 exhibits half-metallic behaviour. The 2D electronic charge density designs in [110] plane indicate the existence of ionic bonding among (O2–-V3+- O2–) and (O2–-Y2+- O2–) bonds to construct all VYO3crystals. The thermodynamic quantities such as coefficient of thermal expansion, Grüneisen parameter, Debye temperature, specific heat capacity have also been analysed up to 1200 K and 80 GPa using Gibbs program. We have used TB-mBJ approximation to evaluate the optical properties by computing the complex dielectric function using with, other parameters are derived. Finally, we have also examined the transport properties i.e., Seebeck coefficient, electrical conductivity, power factor in the range 100–1200 K by semi-classical Boltzmann transport theory.

First-principles investigation of the structural and dynamical stability, electronic and thermal properties of two-dimensional Yn+1Cn (n = 1, 2, and 3) MXenes

This paper studies the structural and dynamical stability, electronic and thermal properties of two-dimensional Yn+1Cn (n = 1, 2, and 3) MXenes in the hexagonal structure. The calculations are carried out using the computational software package QUANTUM-ESPRESSO/PWSCF based on density functional theory (DFT) and the pseudopotential method. The calculated lattice parameters a and c are in good agreement with the previous theoretical and experimental studies. Structural calculations described that Y4C3 is more stable than Y3C2 and Y2C. Analyzing cohesive energy indicates that the structural stability of these compounds increases with increasing n-index due to the increase in the number of stronger bonds between Y and C atoms in the thicker MXene monolayers. The phonon dispersion calculations show that the Yn+1Cn MXenes are dynamically stable at ambient pressure, and it is possible to be experimentally synthesized.Based on the electronic results, it can be argued that the Yn+1Cn has a metallic behavior in the hexagonal structure. Also, the electron charge density distribution confirms the metallic behavior of Yn+1Cn structures. The thermodynamic calculations indicate that enthalpy increases continuously and steadily by increasing pressure and n-index in the Yn+1Cn structures. Generally, for Yn+1Cn (n = 1, 2, and 3) MXenes with the increasing n-index, Debye temperature and stiffness decrease, followed by heat capacity increases.