Function Of Chemical Potential Research Articles

First-principles calculations to investigate structural, electronic, phonon, magnetic and thermal properties of stable halide perovskite semiconductors Cs2GeMnI6 and Cs2GeNiI6

Since, the systematic and extensive study on halide double perovskite’s (HDP’s) have triggered a considerable interest, thus became a new thrust to the scientific research. In this organised report, we present a new promising halide double perovskite structures Cs2GeMnI6 and Cs2GeNiI6 to understand, more in-depth their intrinsic characteristics by means of Density Functional Theory (DFT). Initially, we reported the structural stability of both these crystal structures by evaluating their total ground state energy in stable configuration and cohesive energy at the behest of Brich Murnaghan equation of state. Afterwards, the structural stability is moreover extended to see their corresponding tolerance factor (τ) values and second order elastic constants (SOEC’s). Subsequently, the density functional perturbation theory (DFPT) has been inducted to predict the dynamical context of these ordered systems. Later on, the quantum mechanical treatment of defining their electronic structures by the calibration of mix of two distinct spin-polarised approximation schemes like Perdew-Burke-Ernzerhof Generalised gradient approximation (PBE-GGA) followed by Tran-Blaha modified Becke-Johnson (TB-mBJ). Meanwhile, the unsymmetrical behaviour of electronic structures from their resulting band structures demonstrates the occurrence of spin-magnetic moment of 5 µB and 2 µB/formula unit respectively having the maximum contribution solely coming from the Mn+2 and Ni2+ 3d-transition elements. The evaluation of phonon dependent Grüneisen parameter (γ) defines the possible thermal stability against specific temperature regimes. And finally transport properties as a function of chemical potential (µ-EF) at distinct temperatures has been keenly explored. Therefore, the overall tendency of these designed materials can be envisaged to descript vast implications in various extending applications for conventional spin-based and thermoelectric technologies.

Solving Chemical Absorption Equilibria using Free Energy and Quantum Chemistry Calculations: Methodology, Limitations, and New Open-Source Software.

We developed an open-source chemical reaction equilibrium solver in Python (CASpy, https://github.com/omoultosEthTuDelft/CASpy) to compute the concentration of species in any reactive liquid-phase absorption system. We derived an expression for a mole fraction-based equilibrium constant as a function of excess chemical potential, standard ideal gas chemical potential, temperature, and volume. As a case study, we computed the CO2 absorption isotherm and speciation in a 23 wt % N-methyldiethanolamine (MDEA)/water solution at 313.15 K, and compared the results with available data from the literature. The results show that the computed CO2 isotherms and speciations are in excellent agreement with experimental data, demonstrating the accuracy and the precision of our solver. The binary absorptions of CO2 and H2S in 50 wt % MDEA/water solutions at 323.15 K were computed and compared with available data from the literature. The computed CO2 isotherms showed good agreement with other modeling studies from the literature while the computed H2S isotherms did not agree well with experimental data. The experimental equilibrium constants used as an input were not adjusted for H2S/CO2/MDEA/water systems and need to be adjusted for this system. Using free energy calculations with two different force fields (GAFF and OPLS-AA) and quantum chemistry calculations, we computed the equilibrium constant (K) of the protonated MDEA dissociation reaction. Despite the good agreement of the OPLS-AA force field (ln[K] = -24.91) with the experiments (ln[K] = -23.04), the computed CO2 pressures were significantly underestimated. We systematically investigated the limitations of computing CO2 absorption isotherms using free energy and quantum chemistry calculations and showed that the computed values of μiex are very sensitive to the point charges used in the simulations, which limits the predictive power of this method.

Surface Gibbs free energy analyses of Sr segregation in lanthanum strontium iron oxide

Sr surface segregation in mixed-cation oxides often causes degradation of chemical or electrochemical performance. In this work, the thermodynamic driving force for Sr segregation is investigated to explain the Sr segregation behavior in La0.5Sr0.5FeO3 (LSF). Specifically, Density Functional Theory is used to calculate the surface Gibbs free energy of various surface terminations of cubic (100) LSF as a function of chemical potential and temperature. SrO-terminated surfaces are predicted to be dominant, promoting Sr segregation at high temperatures and low oxygen partial pressure.

Robust and Fragile Majorana Bound States in Proximitized Topological Insulator Nanoribbons.

Topological insulator (TI) nanoribbons with proximity-induced superconductivity are a promising platform for Majorana bound states (MBSs). In this work, we consider a detailed modeling approach for a TI nanoribbon in contact with a superconductor via its top surface, which induces a superconducting gap in its surface-state spectrum. The system displays a rich phase diagram with different numbers of end-localized MBSs as a function of chemical potential and magnetic flux piercing the cross section of the ribbon. These MBSs can be robust or fragile upon consideration of electrostatic disorder. We simulate a tunneling spectroscopy setup to probe the different topological phases of top-proximitized TI nanoribbons. Our simulation results indicate that a top-proximitized TI nanoribbon is ideally suited for realizing fully gapped topological superconductivity, in particular when the Fermi level is pinned near the Dirac point. In this regime, the setup yields a single pair of MBSs, well separated at opposite ends of the proximitized ribbon, which gives rise to a robust quantized zero-bias conductance peak.

First principles investigation on half metallic ferromagnetism properties of cubic VLaO3 compound

In this investigation, we thoroughly examined the equilibrium structural, electrical, magnetic, elastic, thermodynamic, as well as thermoelectric behavior of the vanadium lanthanum oxide perovskite VLaO3. The computations were executed with the FP-LAPW method, as in cooperated in the WIEN2k package that rely on the first principles method, using generalized gradient approximation (PBE-GGA). The explored compound has been observed to be ferromagnetically stable i.e., in FM phase as it has lowest energy in FM state than in paramagnetic phase i.e., in NM phase. The thermodynamical and mechanical stability of the studied VLaO3 compound is also assured by evaluating its formation energy, cohesive energy and second order elastic constants. Furthermore, our computed findings reveal that the studied compound belongs to half metallic perovskites with an energy gap of 2.56 eV in the majority spin and possesses a total magnetic moment of 3.99µB/unit cell. Additionally, the thermal as well as pressure dependence of volume, specific heat capacity, and bulk modulus are also examined with the aid of GIBBS which rely on quasi harmonic Debye theory. Finally, the thermoelectric transport properties are also evaluated as a function of chemical potential in the range extending from −2.0 eV to 2.0 eV for different temperatures at 300 K, 700 K and 1200 K to explore budding possibility of this compound for energy harvesting applications.

Energy storage applicability of novel two-dimensional transition metal nitride alloys: First principle study

Nowadays, saving energy and cost, along with environmental compatibility is a matter for manufacturers of all kinds of devices and goods. Therefore, in this work, it has been tried to investigate a compound which meets this requirement. Here using density functional theory (DFT) and general gradient approximation (GGA), the two-dimensional HfN as a transition metal nitride and its alloys with Mg and Sc are studied (for two types of structures). Cohesive energy, enthalpy of formation energy, and phonon results confirmed the structural, mechanical, thermodynamic, and dynamic stability of the compounds, a semiconducting bandgap has emerged for the Mg alloy of structure 1. Then, the thermoelectric properties of this alloy as a function of chemical potential and temperature have been studied. The thermoelectric power factor and electronic figure of merit exhibit excellent thermoelectric performance at 400 and 600 K which suggest a good candidate for thermoelectric applications. Finally, the quantum capacitance of the pure structures and their Mg alloys have been studied and compared with the other results.

Néel proximity effect at antiferromagnet/superconductor interfaces

Spin-splitting induced in a conventional superconductor weakens superconductivity by destroying spin-singlet and creating spin-triplet Cooper pairs. We demonstrate theoretically that such an effect is also caused by an adjacent compensated antiferromagnet, which yields no net spin-splitting. We find that the antiferromagnet produces N\'eel triplet Cooper pairs, whose pairing amplitude oscillates rapidly in space similar to the antiferromagnet's spin. The emergence of these unconventional Cooper pairs reduces the singlet pairs' amplitude, thereby lowering the superconducting critical temperature. We develop a quasiclassical Green's functions description of the system employing a two-sublattice framework. It successfully captures the rapid oscillations in the Cooper pairs' amplitude at the lattice spacing scale as well as their smooth variation on the larger coherence length scale. Employing the theoretical framework thus developed, we investigate this N\'eel proximity effect in a superconductor/antiferromagnet bilayer as a function of interfacial exchange, disorder, and chemical potential, finding rich physics. Our findings also offer insights into experiments which have found a larger than expected suppression of superconductivity by an adjacent antiferromagnet.

First-principles calculations on structural, electronic, elastic, optical and thermoelectric properties of thallium based chloroperovskites TlMCl3 (M = Zn and Cd)

In this work, we have studied the structural, electronic, elastic, optical and thermoelectric properties of Tl-based chloroperovskite materials TlMCl3 (M = Zn and Cd) in the cubic structure using density functional theory (DFT) which executed in ‘Quantum ESPRESSO’ code. The structural optimization is performed by the Birch-Murnaghan equation of state and the optimized lattice parameters are 4.98Å for TlZnCl3 and 5.225Å for TlCdCl3. The electronic properties show that the compounds are semiconductors with an indirect band gap of 1.5eV and 1.84eV for TlZnCl3 and TlCdCl3, respectively. The elastic properties reveal that the materials are mechanically stable, ductile, and anisotropic. The optical properties of compounds have been studied in range [0−20]eV, they have a high absorption coefficient close to 105cm−1 in the ultraviolet range. The thermoelectric properties are evaluated as a function of chemical potential for different temperatures, and the figure of merit obtained is 0.99 for compounds at room temperature. The results show that the compounds are important materials and can be used as scintillators, as well as for thermoelectric applications.

Tricritical curve of massive chiral Gross-Neveu model with isospin

We reconsider the two-flavor version of the massive, chiral Gross-Neveu model in 1+1 dimensions. Its phase diagram as a function of baryon chemical potential, isospin chemical potential and temperature has previously been explored. We recapitulate the results, adding the missing tricritical curves. They can be determined exactly by extending the standard stability analysis, using fourth order almost degenerate perturbation theory. Results for three different bare masses are presented and discussed.

Probing Optoelectronic and Thermoelectric Properties of Lead-Free Perovskite SnTiO3: HSE06 and Boltzmann Transport Calculations

In order to develop a useful material for the optoelectronic sector with a variety of uses in thermoelectric and optical properties at a reasonable price, we researched SnTiO3, a Pb-free and Sn-based perovskite. We used the most recent density functional theory (DFT) methods, such as the gradient approximation (GGA) approach and the screened hybrid functional (HSE06). The calculated electronic structure yields to an indirect band gap of 2.204 eV along with two different K-points such as (X-Γ) using HSE06. The accomplished optical properties have been examined by dispersion, absorption, reflection, optical conductivity, and loss function against photon energy. The thermoelectric properties and electronic fitness function (EFF) were predicted DFT along with the Boltzmann transport theory. The Seebeck coefficient (S) and related thermoelectric properties such as electronic/thermal conductivity and the Hall coefficient were calculated as a function of chemical potential and carrier density (electrons and holes concentration) for room temperature. It was established that the temperature increases the Seebeck coefficient (S) at every hole carrier concentration. SnTiO3 has good EFF at 300, 500, and 800 K as well. The discovered EFF suggests that this material’s thermoelectric performance rises with temperature and can also be improved through doping. These findings demonstrated the potential of SnTiO3 as an n-type or p-type thermoelectric material depending on the doping.

Regularization issues for a cold and dense quark matter with a chiral imbalance

In this work we investigate the effects of the chiral chemical potential, μ 5, in the two flavor cold and dense quark matter with two different regularization procedures within the Nambu–Jona-Lasinio (NJL SU(2)) model: the Traditional Regularization Scheme (TRS) and the Medium Separation Scheme (MSS). We study the effects of different choices for the parametrization of the model for both regularization schemes. More specifically we were interested in the behavior of the effective quark masses as a function of chiral and quark chemical potentials.

Dipolar Bose-Hubbard model

We study a simple model of interacting bosons on a d-dimensional cubic lattice whose dynamics conserves both total boson number and total boson dipole moment. This model provides a simple framework in which several remarkable consequences of dipole conservation can be explored. As a function of chemical potential and hopping strength, the model can be tuned between gapped Mott insulating phases and various types of gapless condensates. The condensed phase realized at large hopping strengths, which we dub a Bose-Einstein insulator, is particularly interesting: despite having a Bose condensate, it is insulating, and despite being an insulator, it is compressible.

Topological superconductivity in a two-dimensional Weyl SSH model

We study the emergence of topological superconductivity in a two-dimensional Weyl system, composed of stacked Su-Schrieffer-Heeger (SSH) chains. A previous analysis of the model showed that the addition of an attractive Hubbard interaction between spinful electrons leads to a superconducting state that has an intricate pairing structure, but is topologically trivial. Here we consider a pairing interaction that couples spinless fermions on opposite sublattices within the same unit cell. We observe that this physically motivated, momentum-independent pairing interaction induces a topological superconducting state, characterized by a gap function with a nontrivial phase, as well as Majorana and Fermi arc edge states along the edge perpendicular to the direction of the SSH dimerization. In addition, we observe a transition as a function of pairing interaction strength and chemical potential, indicated by a change in the sign of the topological charge carried by each of the four Bogoliubov-Weyl nodes.

The study of optical and thermoelectric behaviour of thalium based flouropervoskite (TlSiF3) for photovoltaic and renewable energy applications by DFT

In the present study, structural, electronic, optical, thermodynamic and thermoelectric properties of perovskites TlSiF3 are explored using first-principles calculations based on density functional theory with different exchange-correlation approximations (LDA, PBE-GGA, WC-GGA, PBE-sol GGA, and mBJ-GGA). The computed structure, electronic and charge density plots using PBE-GGA ​+ ​TB-mBJ approximation show that TlSiF3 is an indirect band gap semiconductor (1.73 ​eV gap along with R– M direction) having ionic and covalent bonding. The optical response is analysed and explained in terms of dielectric function, refractive index, extinction coefficient, optical conductivity, reflectivity, and absorption coefficient in the energy range from 0 to 10 ​eV. The thermoelectric transport behaviour of TlSiF3is computed as a function of temperature and chemical potential, μ−EF. Further, the thermoelectric transport behavior of TlSiF3 is computed as a function of temperature and chemical potential μ−EF (eV). It has been observed that highest value of ZT (0.43) is attained at 1000 ​K with a power factor (PF) of 9.3 ​× ​1010WK−2m−1s−1for a fixed chemical potential. Under varying chemical potential at 300K in n-type region, it exhibits ZT value of 0.98, which is required for thermoelectric devices. Furthermore, pressure as well as temperature dependence of the thermodynamic parameters like Debye temperature, heat capacity, bulk modulus, thermal expansion coefficient, heat capacity, have been estimated with the help of GIBBS program based on quasi-harmonic Debye model.

Partially separated Majorana modes in a disordered medium

Focusing on the implications of recent experiments on Majorana zero modes in semiconductor-superconductor (SM-SC) heterostructures, we critically examine the quantization of the zero-bias differential conductance as a possible unambiguous signature of Majorana physics in the presence of disorder. By numerically calculating the zero-bias conductance (ZBC) maps as function of Zeeman splitting and chemical potential for different disorder realizations, we find that the large topological region associated with the clean system, which is characterized by a quantized ZBC height $2{e}^{2}/h$, breaks up into progressively smaller ``islands'' as the disorder strength increases. For strong disorder we show that the presence of small islands with ZBC value (approximately) equal to $2{e}^{2}/h$, which we refer to as ``quantized islands,'' represents a unique signature of Majorana physics supporting partially separated Majorana modes (ps-MMs). Because of the small area/volume of these quantized islands in the parameter space, observing them in experiments may require sample selection and the systematic scanning of a large volume in the control parameter space. Upon decreasing disorder, the quantized islands increase in size and eventually coalesce into large topological regions. We conclude that the observation of quantized islands with ZBC value approximately equal to $2{e}^{2}/h$ demonstrates unambiguously the presence of the key ingredients necessary for Majorana physics, provides an excellent diagnostic tool for evaluating the disorder strength, and, consequently, represents the next natural milestone in Majorana search.

Assessing the role of surface carbon on the surface stability and reactivity of β-Mo2C catalysts

Transition-metal carbides, e.g., Mo2C, promote industrially important catalytic reactions with activities comparable to precious-metal catalysts. Yet, the nature of the catalytically active sites remains unclear. Herein, density functional theory calculations are applied to systematically assess the stability of low-Miller-index facets of β-Mo2C as a function of carbon chemical potential (μC) and surface-carbon coverage (nC). When reconstruction of surface carbon is considered to characterize β-Mo2C under varying environments, the (111) and (101) surfaces are predicted to be most stable, dominating the Wulff particle surface area across a broad range of μC. The surface-carbon coverage is predicted to steadily increase for all low-index facets under more carburizing reaction conditions, leading to distinct effects on the adsorption energetics for atomic hydrogen and oxygen. Whereas H binding is only slightly affected by surface carbon, O is systematically destabilized. The findings reported indicate that consideration of only bulk-terminated surfaces, and the common focus of theoretical studies on the bulk-truncated, close-packed (100) surface, is likely insufficient to capture the reactivity of the working β-Mo2C catalyst. Similar to metal oxides, β-Mo2C catalysts are predicted to be dynamic materials with surface compositions and reactivities that evolve in response to the environment.

Competition of chiral soliton lattice and Abrikosov vortex lattice in QCD with isospin chemical potential

We investigate the thermodynamics of two-flavor quark matter in presence of nonzero isospin chemical potential and external magnetic field. It is known that at sufficiently high isospin chemical potential, charged pions undergo Bose–Einstein condensation (BEC). The condensate behaves as a superconductor, exhibiting Meissner effect in weak external magnetic fields. Stronger fields stress the superconducting state, turning it first into an Abrikosov lattice of vortices, and eventually destroying the condensate altogether. On the other hand, for sufficiently strong magnetic fields and low-to-moderate isospin chemical potential, the ground state of quantum chromodynamics (QCD) is expected to be a spatially modulated condensate of neutral pions, induced by the chiral anomaly: the chiral soliton lattice (CSL). We map the phase diagram of QCD as a function of isospin chemical potential and magnetic field in the part of the parameter space accessible to a low-energy effective field theory description of QCD. Our main result is an explicit account of the competition between the CSL and the Abrikosov vortex lattice. This is accomplished by adopting a fast numerical algorithm for finding the vortex lattice solution of the equation of motion and the corresponding Gibbs energy. We find that the Abrikosov vortex lattice phase persists in the phase diagram, separating the uniform charged pion BEC phase from the CSL phase. The precise layout of the phase diagram depends sensitively on the choice of the vacuum pion mass.

Layered Pt-Co alloys: Bulk, surface and nanoparticle analysis, based on DFT

Pt-based catalysts are commonly used as cathode materials in various types of fuel cells. In this work we apply DFT calculations combined with cluster expansion method to elucidate the most stable structures of Pt-Co bulk alloy across the full range of Pt (or Co) concentrations. Our calculations reveal high stability of alloy configurations with alternating layers in (001) crystallographic planes of face centered cubic (fcc) structure exclusively occupied either by Pt or Co atoms. In particular, we find that Pt1Co1, Pt2Co1 and Pt3Co1 layered structures (periodically repeated 1–3 Pt layers, separated by single Co layers) have exceptionally high stability with Pt2Co1 possessing the lowest energy of formation among all analysed alloy configurations. Employing ab initio thermodynamics approach, we discuss stability of three types of surface terminations (Miller indices (100), (110) and (111)) for these three layered structures and also for highly symmetric fcc Pt3Co1 configuration, previously identified experimentally. Applying the Wulff construction, we obtain the nanoparticle shapes as functions of chemical potentials of constituent atoms (Pt or Co), allowing for design of computational models of Pt-Co nanoparticles and subsequent analysis of their chemical properties.

Contribution to understanding the phase structure of strong interaction matter: Lee-Yang edge singularities from lattice QCD

We present a calculation of the net baryon number density as a function of imaginary baryon number chemical potential, obtained with highly improved staggered quarks at temporal lattice extent of ${N}_{\ensuremath{\tau}}=4$, 6. We construct various rational function approximations of the lattice data and discuss how poles in the complex plane can be determined from them. We compare our results of the singularities in the chemical potential plane to the theoretically expected positions of the Lee-Yang edge singularity in the vicinity of the Roberge-Weiss and chiral phase transitions. We find a temperature scaling that is in accordance with the expected power law behavior.

High-frequency asymptotics of one integral in the theory of equilibrium radiation of electron gas

It is considered an improper integral that determines the high-frequency asymptotics of the spectral energy distribution of equilibrium radiation in an ideal electron gas. It has been established that in the "high-frequency" limit the asymptotics of this integral has a power-law character, and its value is proportional to the density of the electron gas as a function of temperature and chemical potential for arbitrary degeneracy of electrons. Keywords: equilibrium radiation, spectral energy distribution, electron gas.