Range Of Chemical Potential Research Articles

DFT-based computational investigation of the structural, electronic, and thermoelectric properties oftransition-metal hydride VH2.

Vanadium hydride is of significant interest because of its potential applications in thermoelectric materials and hydrogen storage technologies. Understanding its structural, electronic, and thermoelectric properties is crucial for optimizing its performance in these applications. This study investigates these properties via density functional theory (DFT), revealing key insights into its stability and efficiency as a thermoelectric material. In this work, the structural, electronic, and thermoelectric properties of cubic VH2 were investigated using the GGA approach within the framework of DFT. The band structure and density of states demonstrate the metallic nature of these compounds. Using the semi-empirical Boltzmann's approach implemented in the BoltzTraP code, transport parameters, such as the Seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit as a function of the chemical potential, are computed at a temperature gradient of 500K. For the VH2 compound, the thermal and electrical conductivities and Seebeck coefficient are greater for p-type doping and n-type doping. The moderate values of the figure of merit obtained for these materials indicate that these materials have applicability where small values of thermoelectric efficiency are required, and higher values can harm the process. The maximum values of the Seebeck coefficient for VH2 against chemical potential values ranging between 0.095 and - 0.095eV in the p-type region and n-type region are 2.28µV/K and - 2.27µV/K, respectively. The highest value of electrical conductivity per relaxation time in the chemical potential range between - 0.07 and 0.07eV in the p-type region is 5.3 × 10201/Ωms, and that in the n-type region is 1.97 × 10201/Ωms. The maximum dimensionless figure of merit value for VH2 is 0.020.

Electronic, thermoelectric and magnetic properties of ternary telluride KAlTe2 and KInTe2 from theoretical perspective

First principles study has been applied to the anisotropic ternary KAlTe2 and KInTe2 materials. The energy of each material is optimized to the ground level through WIEN2k code and results are compared with the available theoretical and experimental findings. It is obtained from our results that materials have direct band gap and the calculated band gaps for KAlTe2 and KInTe2 are 1.68 eV and 0.931 eV, respectively. The direct band semiconductors are important for thermoelectric and optical devices. Theoretically the material KAlTe2 is investigated paramagnetic while KInTe2 is diamagnetic after applying GGA. The calculated numerical values of magnetic behavior are small, which suggests the materials exhibit weak magnetism. The semi-classical Boltzmann technique implemented in the BoltzTraP package was used to determine thermoelectric properties including the seebeck coefficient, electrical conductivity, thermal conductivity, and figure of merit (ZT). The seebeck Coefficient value for KInTe2 in N-types region is –11.99 µV/K, the chemical potential range have taken between 0.00 eV to –0.02 eV for the P-type calculated value is material 11.96–8.08 µV/K. The maximum seebeck Coefficient values for the materials KAlTe2 in the N-type region is –0.35 and 0.57 µV/K and P-type region is 5.5–6.7 µV/K, respectively. Calculated numeric values of ZT for both materials are high and materials suited for N-type doping and keeping excellent thermoelectric materials for newly developed semiconductor devices.

DFT assessment on the future prospects of inorganic lead-free halide double perovskites Cs2ABI6 (AB: GeZn, SnBe) for energy conversion technologies

In this study, we employed density functional theory (DFT) calculations to investigate the structural, elastic, electronic, optical, and thermoelectric properties of Cs2ABI6 (AB: GeZn, SnBe) halide double perovskites (HDPs). We employed the full-potential linear augmented plane-wave (FP-LAPW) method, incorporating the generalized gradient approximation (GGA) and Tran-Blaha modified Becke-Johnson (TB-mBJ) approach for the exchange-correlation potential. We found that the HDPs are stable in a cubic structure (space group Fm-3m), as indicated by phase stability analysis, formation energies, tolerance factor, and elastic constants. The compounds exhibits ductile behavior, as assessed by Poisson's and Pugh's ratios. The electronic band structures of Cs2GeZnI6 and Cs2SnBeI6 exhibit indirect band gaps (X-L) of 1.124 eV and 1.551 eV, respectively, as calculated using the TB-mBJ approximation. Optical spectra were evaluated over the 0–13 eV energy range, including the dielectric functions, extinction coefficient, electron energy loss, refractive index, optical conductivity, reflectivity, and absorption coefficient. Additionally, we calculated thermoelectric parameters across a range of chemical potentials and temperatures to assess their suitability for thermoelectric applications. Our results suggest that these compounds are highly promising candidates for both optoelectronic and thermoelectric devices.

Electrically tunable graded photonic crystal lens based on graphene plasmons.

Controlling the nonlinear relationship between surface plasmon polariton (SPP) mode index and chemical potential of graphene can be used in the field of active transformation optics. Here, we propose an electrically tunable 2D Graded Photonic Crystal (GPC) lens based on graphene SPP platform. Our platform comprises a graphene monolayer integrated into a back-gated structure with nano-patterned gate insulators. When the chemical potential of the graphene surface is designed to operate in the nonlinear region, the designed GPC lens can be continuously transformed between a Maxwell's fish-eye lens and a Luneburg lens by tuning the gate voltage. The range of the lens background chemical potential for allowing this transformation is systematically studied. To compensate for the significant errors inherent in the conventional effective medium theory (EMT) during the homogenization of photonic crystals (PCs), we propose a generalized effective medium theory (GEMT). The validity and accuracy of this approach are verified through comparisons with true values (based on rigorous eigenvalue solutions) and EMT values. Due to its advantages of on-site controls and easy fabrication characteristics, the proposed graphene GPC provides a new way for practical on-chip light manipulation.

Comparative First-Principles Study of the Y2Ti2O7/Matrix Interface in ODS Alloys

Oxide-dispersion-strengthened (ODS) alloys generally exhibit extraordinary service performance under severe conditions through the formation of ultrafine nano oxides. Y2Ti2O7 has been characterized as the major strengthening oxide in Fe-based ODS alloys. First-principles energetic analyses were performed to investigate the structural, elastic and interface properties of Y2Ti2O7 in either Fe-based or Ni-based ODS alloys. Y2Ti2O7 has comparable elastic constants to bcc-Fe and fcc-Ni and similar elastic deformation compatibility in Y2Ti2O7-strengthened Fe-based and Ni-based ODS alloys is therefore expected. The Ni/oxide interface has generally better thermostability than Fe/oxide across the whole range of the concerned oxygen chemical potential. Further interface bonding and adhesion calculations revealed that Y2Ti2O7 can enhance the bonding strength of Ni/Y2Ti2O7 through d-d orbital interaction between the interfacial YTi layer and Ni layer, while the interface bonding between the Fe layer and YTi layer is weakened compared to the metal matrix. First-principles calculations suggest that Y2Ti2O7 can be a candidate for strengthening nano-oxides in either Fe-based or Ni-based ODS alloys with well-behaved mechanical properties for fourth-generation fission reactors and further experimental validations are encouraged.

Lee–Yang edge singularities in QCD via the Dyson–Schwinger equations

We take the Dyson–Schwinger Equation approach of QCD for the quark propagator at complex chemical potential to study the QCD phase transition. The phase transition line of the (2+1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(2+1)$$\\end{document}-flavor QCD matter in the imaginary chemical potential region is computed via a simplified truncation scheme, whose curvature is found to be consistent with the one at real chemical potential. Moreover, the computation in the complex chemical potential plane allows us to determine the location of the Lee–Yang edge singularities. We show explicitly that the critical end point coincides with the Lee–Yang edge singularities on the real μB\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu _{B} $$\\end{document} axis. We also investigate the scaling behavior of the singularities and discuss the possibility of extrapolating the CEP from a certain range of chemical potential.

Estimate for the Neutrino Magnetic Moment from Pulsar Kick Velocities Induced at the Birth of Strange Quark Matter Neutron Stars

We estimate the magnetic moment of electron neutrinos by computing the neutrino chirality flip rate that can occur in the core of a strange quark matter neutron star at birth. We show that this process allows neutrinos to anisotropically escape, thus inducing the star kick velocity. Although the flip from left- to right-handed neutrinos is assumed to happen in equilibrium, the no-go theorem does not apply because right-handed neutrinos do not interact with matter and the reverse process does not happen, producing the loss of detailed balance. For simplicity, we model the star core as consisting of strange quark matter. We find that even when the energy released in right-handed neutrinos is a small fraction of the total energy released in left-handed neutrinos, the process describes kick velocities for natal conditions, which are consistent with the observed ones and span the correct range of radii, temperatures and chemical potentials for typical magnetic field intensities. The neutrino magnetic moment is estimated to be μν∼3.6×10−18μB, where μB is the Bohr magneton. This value is more stringent than the bound found for massive neutrinos in a minimal extension of the standard model.

The Equilibrium Stability of 〖CH〗_4 and 〖CO〗_2 on the Calcite (10.4) Surface: an Atomistic Thermodynamics Investigation

The present study utilized the ab initio atomistic thermodynamics technique to assess the stability of pure carbon dioxide and pure methane on the calcite(10.4) systems. The stability of configurations 0.5 ML-A2, 0.75 ML-A2, and 0.75 ML-A1 in CH_4/calcite (10.4) systems was shown to be considerable, but only within a limited range of chemical potential. The 1.0 ML-A1 and 1.0 ML-A2 systems of CH_4/calcite (10.4) demonstrated remarkable stability throughout a wide range of chemical potentials. The predominant stable forms for CO_2/calcite (10.4) systems are the 1.0 ML-B2 and 1.0 ML-A4 structures. The surface free energy phase diagrams demonstrate that CO_2 is more favourable than CH_4 for adsorption on the calcite (10.4) surface.

First-principles study on shape of intrinsic hBN island nucleated during CVD initial growth on Cu(111)

Using the first-principles calculation, the shape of the hexagonal boron nitride (hBN) islands was investigated, with a focus on the edge of the small monolayer hBN islands on Cu(111) and intrinsic nucleation during the CVD initial growth. Several key observations were made. First, desorption does not play a decisive role in shaping the islands. Second, for small islands, there is no chemical potential range where the armchair edge is stable. Third, the bonds between Cu atoms on the surface and N atoms at the edge are strong, whereas the bonds between Cu atoms on the surface and B atoms at the edge are comparatively weaker. Finally, triangular islands with N edge tend to grow more spontaneously than those with B edge because the critical size is smaller for those with N edge across a wide chemical potential range.

An Examination of the Vibrational, Mechanical, Thermoelectric Features and Stability of Novel Half‐Heusler XVIn (X = Pd, Pt) by Density Functional Theory Computation

Modern manufacturing is primarily focused on providing things that are accessible, environmentally conscious, and energy efficient. An effort has been made herein to investigate the compounds that meet these requirements. The full‐potential linearized augmented plane wave method, in Wien2k code, is used to examine the structural, vibrational, mechanical, and transport properties of XVIn (X = Pd, Pt) half‐Heusler compounds. The generalized gradient approximation is used for structural optimization. The computed lattice constants are consistent with earlier theoretical and experimental results. The XVIn (X = Pd, Pt) investigation reveals that the material is inherently ductile and mechanically stable. It is found that XVIn (X = Pd, Pt) has a direct bandgap and a semiconducting property. The modified Becke–Johnson exchange approximation yields bandgap magnitudes of 0.25 and 0.55 eV for PdVIn and PtVIn, respectively. The Boltzmann transport offered by the BoltzTrap software is used to explore thermoelectric characteristics. The values of figure of merit (ZT) obtained for XVIn (X = Pd, Pt) compounds are very close to unity in the chemical potential range from −0.15 to 0.15 eV, indicating that they can be used to make thermoelectric devices with the maximum possible efficiency.

Type-I antiferromagnetic Weyl semimetal InMnTi2

Topological materials have been a main focus of studies in the past decade due to their protected properties that can be exploited for the fabrication of new devices. Among them, Weyl semimetals are a class of topological semimetals with nontrivial linear band crossings close to the Fermi level. The existence of such crossings requires the breaking of either time-reversal (T) or inversion (I) symmetry and is responsible for the exotic physical properties. In this work we identify the full-Heusler compound InMnTi2, as a promising, easy to synthesize, T- and I-breaking Weyl semimetal. To correctly capture the nature of the magnetic state, we employed a novel DFT+U computational setup where all the Hubbard parameters are evaluated from first principles; thus preserving a genuinely predictive character of the theory. We demonstrate that this material exhibits several features that are comparatively more intriguing with respect to other known Weyl semimetals: the distance between two neighboring nodes is large enough to observe a wide range of linear dispersions in the bands, and only one kind of such node's pairs is present in the Brillouin zone. We also show the presence of Fermi arcs stable across a wide range of chemical potentials. Finally, the lack of contributions from trivial points to the low-energy properties makes the materials a promising candidate for practical devices. Published by the American Physical Society 2024

QCD at finite temperature and density - Equation of State

As an important set of thermodynamic quantities, knowledge of the equation of state over a broad range of temperatures and chemical potentials in the QCD phase diagram is crucial for our understanding of strongly-interacting matter. There is a good understanding from first-principles results in lattice QCD, perturbative QCD and chiral effective field theory about the equation of state. However, these approaches are valid in different regimes of the phase diagram, and therefore, a method of providing an equation of state that covers a full range of the phase diagram involves matching together these results with appropriate models in order to fill in the gaps between these regions. Furthermore, with such equations of state, important questions about QCD phase structure can begin to be addressed, such as whether there is a critical point in the QCD phase diagram. In this contribution to the proceedings, equations of state from first-principles and effective theories will be discussed in order to understand how QCD thermodynamics is affected by the presence of a critical point.

Holographic phases of QCD

In this presentation, we will discuss the QCD phase diagram at finite temperature and finite baryon chemical potential using a hardwall holographic AdS/QCD model. We study bulk gravity solutions with appropriate boundary conditions that represent strongly interacting nuclear matter, deconfined quarks, and various possible condensates over a range of baryon chemical potential and temperature.

Exploration of molybdenum oxide precursors: a theoretical study of MoxOy (x = 1-10) clusters.

Transition metal oxides are essential in the synthesis of 2D transition metal-based materials. This study focuses on molybdenum oxide clusters (MoxOy, where x = 1, 2, …, 10) to investigate their stability in varying chemical environments. By integrating density functional theory and a particle swarm optimization algorithm, we evaluated 2133 unique MoxOy cluster structures, identifying 211 most stable isomers, and constructed a comprehensive database of stable configurations. Notably, monocyclic ring-shaped structures with an oxygen-to-molybdenum ratio of 3 : 1 were found to be stable across a wide range of chemical potentials. Our findings elucidate the stability trends and structural evolution mechanisms of MoxOy clusters, enhancing the understanding of molybdenum oxide precursors. This research provides valuable insights into the controlled synthesis of high-quality 2D transition metal-based materials and sheds light on other transition metal oxide precursors.

Complicated point defects in monolayer Ga2S3: stability, midgap states and magnetism

Motivated by recent experimental realization of single-layer α-Ga2S3 [Zheng et al., Adv. Funct. Mater. 31, 2008307(2021)], by using first principles calculations, we systematically investigated the structural, electronic and magnetic properties of single-layer α-Ga2S3 with intrinsic point defects. Although it is a binary semiconductor, its point defects properties are complicated, since there are nonequivalent Ga and S atomic sites in this compound. The most energetically stable vacancy and interstitial defect are VS2 and Si1 for the entire sulfur chemical potential range, while the most energetically favorable antisite defect is dependent on the sulfur chemical potential, such as GaS2 under S-poor condition and SGa1 (SGa2) under S-rich condition. The sulfur vacancy defects (VS1, VS2 and VS2) have induced spin-degenerated defect states in the band gap or the valence band edge, while the gallium vacancy defects (VGa1, and VGa2) have spin-polarized defect states in the band gap or valence band edge with the magnetic moment of 1.30 μB and 1.21μB per defect. The interstitial defects (Gai1, Si1 and Si2) can generate spin-degenerated in-gap defect states. The antisite defects (GaS1, GaS2, GaS3, SGa1, and SGa2) have spin-polarized in-gap defect states with weak magnetic moments of 0.70 μB, 0.69μB, 0.64μB, 0.66μB and 0.65μB per defect. Besides, the origin of the defect states and magnetic moments are examined in detail. These findings are helpful for understanding the defect properties of two dimensional IIIA-VIA binary chalcogenide Ga2S3 and improving its technological applications.

Pairing susceptibility of the two-dimensional Hubbard model in the thermodynamic limit

We compute the diagrammatic expansion of the particle-particle susceptibility via algorithmic Matsubara integration and compute the correlated pairing susceptibility in the thermodynamic limit of the 2D Hubbard Model. We study the static susceptibility and its dependence on the pair momentum $\mathbf{q}$ for a range of temperature, interaction strength, and chemical potential. We show that $d_{x^2-y^2}$-wave pairing is expected in the model in the $U/t\to 0^+ $ limit from direct perturbation theory. From this, we identify key second and third-order diagrams that support pairing processes and note that the diagrams responsible are not a part of charge or spin susceptibility expansions. We find two key components for pairing at momenta $(0,0)$ and $(\pi,\pi)$ that can be well fit as separate bosonic modes. We extract amplitudes and correlation length scales where we find a predominantly local $(\pi,\pi)$ pairing and non-local $\mathbf{q}=(0,0)$ pairs and present the relative weights of these modes for variation in temperature, doping, and interaction strength.

Tunable terahertz bound state in the continuum in graphene metagrating

Recently, high quality (Q) factor resonances governed by quasi-bound state in the continuum (BIC) have attracted increasing attention due to the fascinating electromagnetic resonance properties that provide a new guideline for the design of metasurfaces. In this paper, we propose a graphene metagrating that can support quasi-BIC by introducing periodic perturbations. We discuss the transmission spectrum at normal and oblique incidence. Resonances are analyzed by the multipolar decomposition of radiative power and the electric field distribution to clarify the mechanism of quasi-BIC. The amplitude of quasi-BIC Fano resonance can be tuned by adjusting the chemical potential of graphene, and the modulation amplitude can reach 74%. Furthermore, the relationship between the Q factor of quasi-BIC and the graphene chemical potential is thoroughly investigated. The Q factor of quasi-BIC resonance can achieve linear tunability within a specific range of chemical potential. The further evolution and comparison of the proposed unit cell show that our method of introducing perturbation is universal to some extent. Altogether, the proposed metagrating can be used as an excellent active THz modulator and has potential applications in biochemical sensing, laser and nonlinear optics.

Perovskite quantum‐dots glasses with excellent stability and optical properties for laser projection

AbstractDue to the instability of perovskite quantum‐dots (PQDs), their applications in optoelectronic devices, in reality, are limited. In this paper, Cs(Pb,Sb)Br3 PQDs@glasses were successfully prepared by traditional melting quenching and heat treatment methods. The optical characterization shows that Cs(Pb0.7Sb0.3)Br3 PQDs@glasses has an emission peak of 518 nm and a full width at half maximum of 20 nm, and the photoluminescence quantum yield (PLQY) is 58%. The electronic structure of Cs(Pb0.875Sb0.125)Br3 has been studied by first principles. The stable range of chemical potential of each element in CsPbBr3 is calculated by first principles. It is proved that CsPbBr3 is an excellent PQDs luminescent material. The thermal analysis and temperature‐dependent photoluminescence spectra prove the stability of the PQDs@glass within 200°. The thermal distribution of the sample under laser irradiation is measured by a finite element method. In addition, Cs(Pb,Sb)Br3 PQDs@glasses are combined with AlN‐(Ca,Eu)AlSiN3 ceramic phosphors to prepare phosphor wheels, which shows that these materials have potential application prospects in the field of display.

Constraining free parameters of a color superconducting nonlocal Nambu–Jona-Lasinio model using Bayesian analysis of neutron stars mass and radius measurements

We provide a systematic study of hybrid neutron star equations of state (EOS) consisting of a relativistic density functional for the hadronic phase and a covariant nonlocal Nambu--Jona-Lasinio (nlNJL) model to describe the color superconducting quark matter phase. Changing the values of the two free parameters, the dimensionless vector and diquark coupling strengths ${\ensuremath{\eta}}_{V}$ and ${\ensuremath{\eta}}_{D}$ results in a set of EOS with varying stiffness and deconfinement onset. The favorable parameters are obtained from a systematic Bayesian analysis for which the multimessenger constraint on the neutron star radius at $14{M}_{\ensuremath{\bigodot}}$ and the combined mass-radius constraint for PSR $\mathrm{J}0740+6620$ from NICER experiment are used as the constraints. Additionally, the transition from hadronic matter to deconfined quark matter is constrained to occur above nuclear saturation density. Hybrid stars modeled with these favorable parameters are compatible with the NICER results for the radius of the highest known mass neutron star, PSR $\mathrm{J}0740+6620$. Three new observations interesting for neutron star phenomenology are reported: (i) we show that the constant sound speed (CSS) EOS provides an excellent fit to that of the nlNJL model which implies the squared speed of sound at high densities to be about 0.5 for the optimized parameters; (ii) we give a simple functional form for the mapping between the parameter spaces of these two models valid for the whole range of relevant chemical potentials and (iii) we observe that the special point property of hybrid EOS based on CSS quark matter generalizes to a set of lines consisting of special points when two EOS parameters are varied instead of one. A lower limit for the maximum mass of hybrid stars as a function of the vector coupling strength is obtained.

DFT analogue of prospecting the spin-polarised properties of layered perovskites Ba2ErNbO6 and Ba2TmNbO6 influenced by electronic structure

Since the unexpected accelerated discovery of half-metallic perovskites is continuously on the rise both from basic sciences and application-oriented sides. Herein, for the first time in this carried research work, we significantly delivered a detailed analysis on one of experimentally synthesized perovskite structure Ba2ErNbO6 and in related to Ba2TmNbO6 within the realm of unified density functional theory. Initially, the structural stability of two molecular perovskite structures were critically established interms of their total ground state and cohesive energies by the expendition of Brich Murnaghan equation of state. Also, the tolerance factor (τ) oversees the cubic structural stability without possessing any geometrical strains. More likely, the density functional perturbation theory (DFPT) has been calibrated to perceive the dynamical context of these layered structures. Also, from the understandings of second order elastic and mechanical parameters adresses their suitable ductile characteristics. The quantum mechanical refinement of their intrinsic electronic structures were systematically tuned by the exploitation of Generalised gradient approximation (GGA), on-site Hubbard scheme (GGA + U) selected to the strongly correlated electrons of particular angular momentum and modified Becke-Johnson (mBJ) potential. Moreover, the two-dimensional representation of asymmetric density of states (DOS) pinned around the Fermi-level (EF) and the interpretation linked to their corresponding spin-polarised band structures signatures the well-known half-metallic nature. Subsequently, the transport properties especially the value of figure of merit (ZT) equals to unity (1) along the selected chemical potential range at different temperatures. The summed-up properties and the overall tendency triggers the possibility of these materials to register their extending applications in spintronics, thermoelectrics, nanoengineering, and radioisotope generator perspectives.