Density Of States Function Research Articles

Implementation of the Su-Schrieffer-Heeger Model in the Self-Assembly Si-In Atomic Chains on the Si(553)-Au Surface.

Indium-decorated Si atomic chains on a stepped Si(553)-Au substrate are proposed as an extended Su-Schrieffer-Heeger (SSH) model, revealing topological end states. An appropriate amount of In atoms on the Si(553)-Au surface induce the self-assembly formation of trimer SSH chains, where the chain unit cell comprises one In atom and two Si atoms, confirmed by scanning tunneling microscopy images and density functional calculations. The electronic structure of the system, examined through scanning tunneling spectroscopy, manifests three electron bands within the Si-In chain, accompanied by additional midgap topological states exclusively appearing at the chain's end atoms. To elucidate the emergence of these topological states, a tight-binding model for a finite-length-extended SSH chain is proposed. Analysis of the energy spectra, density of states functions, and eigenfunctions demonstrates the topological nature of these self-assembled atomic chains.

Effects of Alloying Element on Hydrogen Adsorption and Diffusion on α-Fe(110) Surfaces: First Principles Study

Based on first principles density functional theory (DFT) methods, this study employed the Cambridge Serial Total Energy Package (CASTEP) module within Materials Studio (MS) software under the generalized gradient approximation to investigate the adsorption, diffusion behavior, and electronic properties of hydrogen atoms on α-Fe(110) and α-Fe(110)-Me (Mn, Cr, Ni, Mo) surfaces, including calculations of their adsorption energies and density of states (DOS). The results demonstrated that doping with alloy atoms Me increased the physical adsorption energy of H2 molecules on the surface. Specifically, Mo doping elevated the adsorption energy from −1.00825 eV to −0.70226 eV, with the largest relative change being 30.35%. After doping with Me, the chemical adsorption energy of two hydrogen atoms does not change significantly, among which doping with Cr results in a decrease in the chemical adsorption energy. Building on this, further analysis of the chemical adsorption of single atoms on the surface was conducted. By comparing the adsorption energy and the bond length between a hydrogen atom and iron/dopant metal atom, it was found that Mo doping has the greatest impact, increasing the bond length by 58.58%. Analysis of the DOS functions under different doping conditions validated the interaction between different alloy elements and H atoms. Simultaneously, simulations were carried out on the energy barrier crossed by H atoms diffusing into the metal interior. The results indicate that Ni doping facilitates the diffusion of H atoms, while Cr, Mn, and Mo hinder their diffusion, with Mo having the most significant effect, where its barrier is 21.88 times that of the undoped surface. This conclusion offers deep insights into the impact of different doping elements on hydrogen adsorption and diffusion, aiding in the design of materials resistant to hydrogen embrittlement.

Prediction of impurity spectrum function by deep learning algorithm

By using the numerical renormalization group (NRG) method, we construct a large dataset with about one million spectral functions of the Anderson quantum impurity model. The dataset contains the density of states (DOS) of the host material, the strength of Coulomb interaction between on-site electrons (U), and the hybridization between the host material and the impurity site (Γ). The continued DOS and spectral functions are stored with Chebyshev coefficients and wavelet functions, respectively. From this dataset, we build seven different machine learning networks to predict the spectral function from the input data, DOS, U, and Γ. Three different evaluation indexes, mean absolute error (MAE), relative error (RE) and root mean square error (RMSE), are used to analyze the prediction abilities of different network models. Detailed analysis shows that, for the two kinds of widely used recurrent neural networks (RNNs), gate recurrent unit (GRU) has better performance than the long short term memory (LSTM) network. A combination of bidirectional GRU (BiGRU) and GRU has the best performance among GRU, BiGRU, LSTM, and BiLSTM. The MAE peak of BiGRU+GRU reaches 0.00037. We have also tested a one-dimensional convolutional neural network (1DCNN) with 20 hidden layers and a residual neural network (ResNet), we find that the 1DCNN has almost the same performance of the BiGRU+GRU network for the original dataset, while the robustness testing seems to be a little weak than BiGRU+GRU when we test all these models on two other independent datasets. The ResNet has the worst performance among all the seven network models. The datasets presented in this paper, including the large data set of the spectral function of Anderson quantum impurity model, are openly available at https://doi.org/10.57760/sciencedb.j00113.00192.

The quantum density of states and distribution functions of the helium-3: Wigner approach in path integral Monte Carlo simulations

A new path integral representation of the quantum density of states (DOS) and distribution functions of strongly correlated fermions are derived in the Wigner formulation of quantum mechanics. A new path integral Monte Carlo approach to calculate DOS and thermodynamic functions is suggested. Using 3 He as an interesting example, we calculate the DOS, internal energy distribution (IED), momentum distribution functions (MDFs), spin-resolved radial distribution functions at different densities and temperatures. The physical meaning and parameters of exchange-correlation holes, the quantum oscillations of IEDs and DOS as well as the high-momentum asymptotics (‘quantum tails’) of MDFs have been considered and explained.

Phase-space path-integral representation of the quantum density of states: Monte Carlo simulation of strongly correlated soft-sphere fermions.

The Wigner formulation of quantum mechanics is used to derive a path-integral representation of the quantum density of states (DOS) of strongly correlated fermions in the canonical ensemble. A path-integral Monte Carlo approach for the simulation of DOS and other thermodynamic functions is suggested. The derived Wigner function in the phase space resembles the Maxwell-Boltzmann distribution but allows for quantum effects. We consider a three-dimensional quantum system of strongly correlated soft-sphere fermions at different densities and temperatures. The calculated properties include the DOS, momentum distribution functions, spin-resolved radial distribution functions, potentials of mean force, and related energy levels obtained from the Bohr-Sommerfeld condition. We observe sharp peaks on DOS and momentum distribution curves, which are explained by the appearance of fermionic bound states.

Oxygen Dependence of Formation, Electronic State Transition, and Spin Polarization for Anatase TiO2: A Comprehensive Study

The stability, geometry, microstructure, and specie combination together with the electronic states of the anatase TiO2 with oxygen defect content of 0%, 3.125%, 6.25%, and 12.5% have been intensively studied within the framework of the density functional theory method. The results show that the TiO2 with an oxygen defect is not as stable as intrinsic TiO2. The compound formation enthalpy Ef and the oxygen defect formation energy value tend to be larger for a higher defect content, and the oxygen defect gets harder to be formed. The bonds within the TiO6 polyhedron are different and not geometrically symmetrical. The bond strengths show distinct diversity, and the primitive cell of anatase TiO2 show spatial expansion when there are oxygen defects. All bands moved down to the low energy region, and two impurity energy band levels emerged for the anatase TiO2 with oxygen defect. The energy band gap is decreased from 3.085 eV to 1.165 eV, 1.0015 eV, and 0.43 eV. There are generally 7 peaks for the spin density of states function, corresponding to their 5 main bands. For the anatase TiO2 with an oxygen defect content of 12.5%, the spin density of states functions are not horizontal ordinate symmetrical near −1.12 eV and 0.31 eV. They are formed by oxygen defect energy levels, which is the result of the Ti d and O p state electron polarization. Transitions from weak paramagnetic to antiferromagnetic are found for the anatase TiO2 with oxygen defect.

Impact of edge functionalization on electron field-emission characteristics of carbon nanotubes: A theoretical approach

A theoretical approach using first-principle calculations of the density of states (DOS) of functionalized carbon nanotubes (CNTs) is carried out to understand their enhanced electron field emission (FE) properties. The theoretical functionalization of CNTs is perceived using hydrogenation (H/O–H) and oxidation methods. In order to investigate the enhancement in the FE properties of functionalized CNTs, both single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) are studied. The work function is observed to be more decreased in case of zigzag SWCNT (φ = 3.32 for oxygenated SWCNT) as compared to others SWCNT. The dependence of DOS on zigzag/armchair edge functionalization has also been investigated to reveal the impact of DOS on FE. The observed results indicate that edge functionalization of CNTs leads to significant changes in the band structure, DOS, and work functions. The shifting of DOS away from the Fermi level and decrease in work function is evidenced owing to the reduction in the curvature effect of CNT. Also, due to enhanced DOS near the Fermi level, making them a better proposition for FE applications. Our calculations provide an in-depth insight into the functionalization mechanism to understand the enhanced FE properties from them.

Networks of materials: Construction and structural analysis

AbstractModeling and analysis of the materials universe is an emerging area of research with many important applications in materials science. The main goal is to create a map of materials which allows not only to visualize and navigate the materials space, but also reveal complex relationships and “connections” among materials and potentially find clusters of materials with similar properties. In this paper, we consider the problem of mapping and exploring the materials universe using network science tools and concepts. The networks are based on the open‐source materials data repository AFLOW.org where each material is represented as a node, and each pair of nodes is connected by a link if the respective materials exhibit a high level of similarity between their Density of States (DOS) functions. We discuss the importance of similarity measure selection, investigate basic structural properties of the resulting networks, and demonstrate advantages and limitations of the proposed approaches. Materials networks, similarity measures, DOS function, materials informatics, network analysis, clique.

Haeckelite boron nitride as nano sensor for the detection of hazardous methyl mercury

A new two-dimensional (2D) member in the boron nitride family, haeckelite BN (haeck-BN) is proposed as a nanosensor for the detection of environmental hazardous material, methyl mercury (CH3Hg). Using first principles-based dispersion corrected density functional calculations, we have studied interaction of CH3Hg with haeck-BN to understand its role as toxic gas sensor. The interaction of CH3Hg with haeck-BN is validated by calculating the adsorption energy and electronic density of states (DOS). The change in DOS and work function (WF) upon adsorption of CH3Hg molecules further confirms the sensing ability of haeck-BN. In the pristine form, haeck-BN shows weak interaction towards CH3Hg with adsorption energy of −0.45 eV. To tune the sensing and electronic properties of haeck-BN, we doped haeck-BN with Al, S, Si, and P atoms. The substitutions were found to alter the electronic properties of haeck-BN, turning it from semiconducting to metallic. However, with the substitution of heteroatom, a significant increment in the adsorption energy is observed in the range of −1.9 eV to −3.8 eV. Our finding suggests that haeck-BN can be utilized as a sensor for the detection of hazardous toxins.

Carriers disappear from conduction band edge with oscillations for certain values of electric and parallel magnetic fields

An attempt has been made to study the energy-spectrum of conduction electrons and the corresponding density-of-states (DOS) functions in semiconductors with the presence of electric and parallel magnetic fields. It is found for n-GaAs that the isotropic parabolic un-perturbed energy spectrum exhibits anisotropic dispersion with energy dependent mass anisotropy in the presence of an external electric field. This anisotropic dispersion relation transforms to an isotropic one under the approximation:k2x≈1/3k2; where kx also, the band-gap of semiconductor increases with both of electric and parallel magnetic fields. Is the x-component of wave-vector ¯k . Furthermore, the carriers are disappeared from the conduction band-edge without oscillations in the case of only electric field. However, carriers vanish with oscillations with the presence of both the electric and magnetic fields. The well-known result of the DOS functions for parabolic band has been retrieved, under certain limiting conditions, from our generalized expressions. Our theoretical observations of band-gap enhancement and the DOS functions are correlated with the nature of the experimental findings.

Discrete and Weyl density of states for photonic dispersion relation

The current density of states (DOS) calculations do not take into account the essential discreteness of the state space, since they rely on the unbounded continuum approximation. Recently, discrete DOS based on the quantum-mechanically allowable minimum-energy interval has been introduced for the quadratic dispersion relation. In this work, we consider systems exhibiting a photonic (photon-like) dispersion relation and calculate the related density and number of states (NOS). Also, a Weyl’s conjecture-based DOS function is calculated for photons and acoustic phonons at a low-frequency limit, by considering the bounded continuum approach. We show that the discrete DOS function reduces to expressions of bounded and unbounded continua in the appropriate limits. The fluctuations in discrete DOS completely disappear under accumulation operators. It is interesting that relative errors of NOS and DOS functions with respect to discrete ones have exactly the same character as the ones of the quadratic dispersion relation. Furthermore, the application of discrete and Weyl DOS for the calculation of internal energy of a photon gas is presented and the importance of discrete DOS is discussed. It is shown that the discrete DOS function given in this work needs to be used whenever the low energy levels of a physical system are heavily occupied.

Two-dimensional delafossite cobalt oxyhydroxide as a toxic gas sensor

To the chain of development of 2D materials, recently synthesized ultrathin cobalt oxy-hydroxide (CoOOH) nano sheets gain potential interest due to its structural, electronic and other properties. We have studied the interaction mechanism of two toxic gases hydrogen peroxide (H2O2) and ammonia (NH3) adsorbed over 2D CoOOH to understand the role of 2D CoOOH as a toxic gas sensor. We employ first principles based dispersion corrected density functional calculations to study the sensing behavior of 2D CoOOH towards H2O2 and NH3 by calculating adsorption energy, electronic band structure, density of states (DOS) and work function. The electronic band structure, DOS and work function of 2D CoOOH are modulated after adsorption of H2O2 and NH3 molecules. Adsorption of gas molecules confirms the sensing behavior of 2D CoOOH towards these molecules and depicts its use in a sensing device. The full phonon dispersion curves and phonondensity of states reveal the dynamical stability of 2D CoOOH. The calculated adsorption energy of H2O2 and NH3 molecules is −0.532 and −0.460 eV respectively which indicates the strong physisorption of these gases over 2D CoOOH. The ultrafast recovery time of 1239 and 1203 ns respectively were found for H2O2 and NH3 on 2D CoOOH. The work function which is 6.29 eV found for 2D CoOOH, decreases to 5.63 eV for H2O2 as it follows the reduction process on 2D CoOOH, and increases to 6.44 eV for NH3 molecules as it acts as oxidation gas on CoOOH. Our study reveals that the 2D CoOOH can be a better sensor for the H2O2 and NH3 gases than some traditional two-dimensional materials.

A new flatland buddy as toxic gas scavenger: A first principles study

Recently predicted and grown new single element two dimensional (2D) material borophene gathered tremendous research interest due to its structural, electronic and other properties. Using first principles based dispersion corrected density functional calculations, we have studied interaction of two toxic gases phosgene (COCl2) and carbon monoxide (CO) with borophene to understand the role of borophene as biosensor and carriers in drug delivery. The sensing behaviour of borophene towards COCl2 and CO has been studied by calculating the binding energy and electronic density of states (DOS). The change in the band structure, DOS, charge density and work function (WF) upon adsorption of gas molecules further confirms the sensing properties of borophene towards these molecules. The binding energy for COCl2 and CO molecules on borophene is −0.306 eV and −0.15 eV respectively which indicates that the COCl2 is adsorbed more favourably than CO over borophene. The WF is enhanced by 0.193 eV and 0.051 eV after the adsorption of COCl2 and CO over borophene. Short recovery time of 148 ns and 37 ns for COCl2 and CO has been predicted. These findings show that the borophene can be used as nanosensor to detect COCl2 and CO.

Fermi integral and density-of-states functions in a parabolic band semiconductor degenerately doped with impurities forming a band tail

We provide the energy spectrum of an electron in a degenerately doped semiconductor of parabolic band. Knowing the energy spectrum, the density-of-states (DOS) functions are obtained, considering the Gaussian distribution of the potential energy of the impurity states, showing a band tail in them e.g., energy spectrum and density-of-states. Therefore, Fermi integrals (FIs) of DOS functions, having band tail, are developed by the exact theoretical calculations of the same. It is noticed that with heavy dopings in semiconductors, the total FI demonstrates complex functions, containing both real and imaginary terms of different FI functions. Their moduli possess an oscillatory function of $$\eta $$ (reduced $$\hbox {Fermi energy} = E_{\mathrm{f}}/k_{\mathrm{B}}T$$ , $$k_{\mathrm{B}}$$ is the Boltzmann constant and T is the absolute temperature) and $$\eta _{e}$$ (impurity screening potential), having a series solutions of confluent hypergeometric functions, $$\Phi (a, b; z)$$ , superimposed with natural cosine functions of angle $$\theta $$ . The variation of $$\theta $$ with respect to $$\eta $$ indicated a resonance at $$\eta =1.5$$ . The oscillatory behaviour of FIs show the existence of ‘band-gaps’, both in the real as well as in the forbidden bands as new band gaps in the semiconductor.

Statistics of Point Vortex Turbulence in Non-neutral Flows and in Flows with Translational and Rotational Symmetries

A theory (Esler and Ashbee in J Fluid Mech 779:275–308, 2015) describing the statistics of N freely-evolving point vortices in a bounded two-dimensional domain is extended. First, the case of a non-neutral vortex gas is addressed, and it is shown that the density of states function can be identified with the probability density function of an infinite sum of independent non-central chi-squared random variables, the details of which depend only on the shape of the domain. Equations for the equilibrium energy spectrum and other statistical quantities follow, the validity of which are verified against direct numerical simulations of the equations of motion. Second, domains with additional conserved quantities associated with a symmetry (e.g., circle, periodic channel) are investigated, and it is shown that the treatment of the non-neutral case can be modified to account for the additional constraint.

Electromagnetic response of chains of spheres: Dynamics to quasi-statics

We calculate the response of infinite chains of spherical particles using different techniques for carrying out lattice sums. The focus is on efficient and accurate methods, their use in establishing Green’s functions connected with density of states functions, their low-frequency limits and their use in homogenization theories.

Phase transitions in a two-dimensional antiferromagnetic Potts model on a triangular lattice with next-nearest neighbor interactions

Phase transitions (PTs) and frustrations in two-dimensional structures described by a three-vertex antiferromagnetic Potts model on a triangular lattice are investigated by the Monte Carlo method with regard to nearest and next-nearest neighbors with interaction constants J1 and J2, respectively. PTs in these models are analyzed for the ratio r = J2/J1 of next-nearest to nearest exchange interaction constants in the interval |r| = 0–1.0. On the basis of the analysis of the low-temperature entropy, the density of states function of the system, and the fourth-order Binder cumulants, it is shown that a Potts model with interaction constants J1 0 and J2 < 0, frustrations arise in the range 0.5 < |r| < 1.0, while, in the interval 0 ⩽ |r| ⩽ 1/3, the model exhibits a second-order PT.

Mechanisms of temperature- and field-dependent effective drift mobilities and impact ionization coefficients in amorphous selenium

The mechanisms of electric-field- and temperature-dependent effective drift mobility and impact ionization coefficient of both holes and electrons in amorphous selenium (a-Se) are investigated in this paper. An analytical model for the microscopic mobility, momentum relaxation mean free path, and hence the effective drift mobility and impact ionization coefficient of carriers, is proposed in this paper by considering the density of states distribution, field enhancement release rate from the shallow traps, and carrier heating. The results of the model are fitted with the published experimental results on effective mobility and impact ionization coefficient with wide variations of the applied electric field and temperature. A better fitting considering thermally activated tunneling for the field-enhancement release rate indicates that the effective drift mobility at extremely high fields is mainly controlled by the neutral defect states near the band edges. The density of state function near the band edges, consisting of an exponential tail and a Gaussian peak, can successfully describe the electric-field- and temperature-dependent effective drift mobility characteristics in a-Se. The momentum relaxation mean free path decreases with increasing field and decreasing temperature, which is required to describe the electric-field- and temperature-dependent behaviors of impact ionization coefficient in a-Se.

Density of states and excitonic condensation in the double layer correlated systems

We consider the single-particle density of states (DOS) in the strongly correlated double layer (DL) system, without applied external fields. We demonstrate an unusual collapse effect in the spectrum of the normal single-particle spectral function at the particular high-symmetry point corresponding to the specific bunching-point solution of the chemical potential in the Frenkel channel. We show that at the low-temperature limit the anomalous spectral function obeys a concave like structure, which is directly related to the interlayer pair formation and condensation. We calculate the normal DOS functions, and we find their temperature dependence for different values of the interlayer Coulomb interaction parameter. We show that the normal electron and hole DOS functions demonstrate typical condensates double peak structures on the background of the excitonic pair formation quasiparticle spectra and we have found the evidence of the hybridization gap in the case of high-temperature limit, and small interlayer coupling parameter. Meanwhile, we show a possible crossover from the excitonic condensate regime into the band insulator state. The structure of the normal DOS spectra, in the Frenkel channel and for the strong interlayer coupling regime, is found gapless for all temperature limits, which clearly indicates the strong coherence effects in the DL structure, and the excitonic condensates therein. We have shown that the excitonic pair formation and pair condensation occur simultaneously in the DL system, in contrast with the purely three-dimensional (3D) or two-dimensional cases (2D), discussed previously.

Study of electronic and optical properties of Bi0.5Na0.5TiO3, BiTiO3, NaTiO3 crystals using full potential linear argumented plane wave method

We studied the optical and electronic properties of Bi0.5Na0.5TiO3, BiTiO3, NaTiO3 compounds such as density of state function, refraction index, optical conductivity and energy gap. Calculations were performed in the framework of density functional theory (DFT), using the full-potential linearized augmented plane wave (FP-LAPW) method with generalized gradient approximation (GGA) for correlation potential, optical properties were obtained using Kramer–Kronig transformations in the imaginary dielectric tensor. The result shows that there is a remarkable difference between NaTiO3 and BiTiO3 compounds by Bi0.5Na0.5TiO3 compound for the mentioned quantities Bi0.5Na0.5TiO3, NaTiO3, BiTiO3 compounds are a direct band gap insulator with energy gap of about 1.97eV, 2.2eV, 2.6eV, respectively.