Semiclassical Theory Research Articles

Thermodynamic Optoelectronic and Photovoltaic Properties of Al-doped Boron Arsenide alloy

Abstract This study investigates the electronic, optical, thermoelectric, and thermodynamic properties of BAs using Density Functional (DFT) and Semi-Classical Boltzmann theories. The band gap, initially determined by the GGA approximation, is refined using the TB-mBJ method, HSE, SOC and GGA+U inelectronic property. Our calculations show a significant reduction in the band gap closed by the various approaches when aluminum (Al) is introduced into the BAs lattice, extending the material`s light absorption spectrum into the visible range. The thermoelectric properties of both pure and Al-doped BAs are evaluated near the Fermi level at various temperatures. The positive Seebeck coefficient indicates p-type behavior, and Al incorporation enhances electrical conductivity. The mechanical properties indicate that the compounds are stable. These findings denote potential applications for Al-doped BAs in thermoelectric and optoelectronic devices.

Potential thermoelectric material Tl3XS4 (X = V, Nb, Ta) with ultralow lattice thermal conductivity.

The demand for sustainable energy solutions has driven intensive research into advanced thermoelectric (TE) materials, to harness waste heat for efficient power generation. Recently, several studies have revealed that Tl3VS4 possesses an ultralow lattice thermal conductivity, despite its simple body-centered cubic lattice structure. This paper focuses on the TE properties of Tl3XS4 (X = V, Nb, Ta) compounds through a systematic exploration utilizing first-principles calculations and semiclassical Boltzmann transport theory. The results of the AIMD simulation and phonon calculation reveal the excellent dynamic stability and thermal stability of Tl3XS4 at 300, 500, and 700 K. Moreover, we find that the Tl3XS4 compounds present ultralow lattice thermal conductivity (<0.5 W m-1 K-1 at 300 K), and the nanostructure strategy is effective. Based on the outstanding Seebeck coefficient and ultralow lattice thermal conductivity, the optimal ZT values of Tl3VS4, Tl3NbS4, and Tl3TaS4 at 300 K are determined to be 1.17 (p-type), 0.84 (n-type), and 0.65 (p-type), respectively. Additionally, at each considered temperature, the maximum ZT values of p-type (n-type) Tl3XS4 follow the order: Tl3VS4 > Tl3NbS4 > Tl3TaS4 (Tl3NbS4 > Tl3VS4 > Tl3TaS4). Our results demonstrate that Tl3XS4 (X = V, Nb, Ta) compounds are promising thermoelectric materials. This exhaustive research enhanced our nuanced comprehension of the electronic, dynamic, and thermoelectric attributes of Tl3XS4 (X = V, Nb, Ta), thereby offering valuable insights into the TE field.

Equivalence of semiclassical and response theories for second-order nonlinear ac Hall effects

Equivalence of semiclassical and response theories for second-order nonlinear ac Hall effects

Impact of strain and electron–phonon coupling on thermoelectric performance of Germanene

This manuscript describes the thermoelectric properties of monolayer germanene under the influence of biaxial strain using the combined approach of ab initio and semi-classical Boltzmann transport theory. To achieve excellent precision in the estimation of the thermoelectric behavior of strained germanene, the research delves into the temperature-dependent scattering time, particularly emphasizing the electron–phonon coupling effect. Incorporating both optical and acoustic phonons is always crucial and key for precisely estimating the scattering time, surpassing the limitations of the deformation potential approximation method. By examining the impact of strain on monolayer germanene and accounting for its scattering time, this approach provides a more practical means of gauging the thermoelectric performance of germanene under the presence of bi-axial strain. Moreover, the study extends its analysis to doped germanene with bi-axial strain, employing the rigid band approximation to investigate its thermoelectric performance. The research extensively estimates the transport properties for both intrinsic and extrinsic germanene, utilizing the hybrid functional HSE06. Additionally, the lattice thermal conductivity of germanene is estimated and compared for the strained and unstrained conditions. The analysis of thermal conductivity involves considering the effects of group velocity and phonon scattering time, providing insights into the nature of heat transport in strained germanene systems. Overall, this comprehensive study contributes to a deeper understanding of the thermoelectric properties of germanene under strain and lays the foundations for potential applications in electronic and thermal devices.

Combined first-principles and Boltzmann transport theory methodology for studying magnetotransport in magnetic materials

Unusual magnetotransport behaviors, such as temperature-dependent negative magnetoresistance (MR) and bowtie-shaped MR, have puzzled us for a long time. Although several mechanisms have been proposed to explain these phenomena, the absence of comprehensive quantitative calculations has made these explanations less convincing. In our work, we introduce a methodology to study magnetotransport behaviors in magnetic materials. This approach integrates the anomalous Hall conductivity induced by the Berry curvature, with a multiband ordinary conductivity tensor, employing a combination of first-principles calculations and semiclassical Boltzmann transport theory. Our method also incorporates the temperature dependence of the relaxation time and the anomalous Hall conductivity, as well as the field dependence of the anomalous Hall conductivity. We initially test this approach on models, obtaining distinct behaviors of magnetoresistance and Hall resistivity across several types of magnetic materials, and then apply it to a Weyl semimetal Co3Sn2S2. The results, which align well with experimental observations in terms of magnetic field and temperature dependencies, demonstrate the efficacy of our approach. This methodology provides a comprehensive and efficient means to understand the underlying mechanisms of the unusual complex behaviors observed in magnetotransport measurements in magnetic materials. Published by the American Physical Society 2024

Comparative analysis of electronic and thermoelectric properties of strained and unstrained IrX3 (X = P, As) skutterudite materials

Abstract The electronic and thermoelectric properties of unfilled IrP3 and IrAs3 skutterudites materials under hydrostatic pressures are investigated using density functional theory (DFT) combined with semi-classical Boltzmann transport theory. Calculations of the elastic properties and phonon frequencies for both strained and unstrained materials demonstrate that they are mechanically and dynamically stable, with ductility varying based on the applied pressure. For pressures ranging from 0 to 30 GPa, the band structure calculations with the GGA+TB-mBJ approximation reveal that the band gap varies from 0.400 to 0.144 eV for IrP3 and from 0.341 to 0.515 eV for IrAs3. At 0 GPa, IrAs3 exhibits a direct band gap, whereas IrP3 has an indirect band gap. As pressure increases, IrAs3 undergoes a transition from a direct to an indirect band gap above 10 GPa, while IrP3 maintains its indirect band gap characteristic throughout the pressure range. &amp;#xD;The thermoelectric properties, at various pressures and temperatures between 300 and 1200 K, are also computed. These properties include the Seebeck coefficient, electrical conductivity, thermal conductivity (both electronic and lattice contributions), and relaxation time. The ideal conditions for efficient thermoelectric properties in IrAs3 are achieved at 30 GPa and 1200 K, with an optimal n-type doping concentration of 56×1019 cm-3, resulting in a ZT of 0.68. For IrP3, a ZT of approximately 0.46 is obtained at 600 K and 5 GPa, with a p-type doping concentration of 6.0×1018 cm-3.&amp;#xD;The present study provides valuable insights into the behavior of skutterudite materials under strain, offering pathways for enhancing their performance in practical applications.&amp;#xD;

Correlations and signaling in the Schrödinger–Newton model

Abstract The Schrödinger–Newton (SN) model is a semi-classical theory in which, in addition to mutual attraction, massive quantum particles interact with their own gravitational fields. While there are many studies on the phenomenology of single particles, correlation dynamics in multipartite systems is largely unexplored. Here, we show that the SN interactions preserve the product form of the initial state of a many-body system, yet on average agreeing with classical mechanics of continuous mass distributions. This leads to a simple test of the model, based on verifying bipartite gravitational evolution towards non-product states. We show using standard quantum mechanics that, with currently accessible single-particle parameters, two masses released from harmonic traps get correlated well before any observable entanglement is accumulated. Therefore, the SN model can be tested with setups aimed at observation of gravitational entanglement with significantly relaxed requirements on coherence time. We also present a mixed-state extension of the model that avoids superluminal signaling.

Semiclassical instanton theory for reaction rates at any temperature: How a rigorous real-time derivation solves the crossover temperature problem.

Instanton theory relates the rate constant for tunneling through a barrier to the periodic classical trajectory on the upturned potential energy surface, whose period is τ = ℏ/(kBT). Unfortunately, the standard theory is only applicable below the "crossover temperature," where the periodic orbit first appears. This paper presents a rigorous semiclassical (ℏ → 0) theory for the rate that is valid at any temperature. The theory is derived by combining Bleistein's method for generating uniform asymptotic expansions with a real-time modification of Richardson's flux-correlation function derivation of instanton theory. The resulting theory smoothly connects the instanton result at low temperature to the parabolic correction to Eyring transition state theory at high-temperature. Although the derivation involves real time, the final theory only involves imaginary-time (thermal) properties, consistent with the standard version of instanton theory. Therefore, it is no more difficult to compute than the standard theory. The theory is illustrated with application to model systems, where it is shown to give excellent numerical results. Finally, the first-principles approach taken here results in a number of advantages over previous attempts to extend the imaginary free-energy formulation of instanton theory. In addition to producing a theory that is a smooth (continuously differentiable) function of temperature, the derivation also naturally incorporates hyperasymptotic (i.e., multi-orbit) terms and provides a framework for further extensions of the theory.

Semiclassical Transition State Theory (SCTST) Rate Coefficients for the Unimolecular Decomposition of the Ethoxy (CH3CH2O) Radical.

The thermal unimolecular decay of ethoxy is important in high-temperature combustion environments where the ethoxy radical is a key reactive intermediate. Two dissociation pathways of ethoxy, including the β-C-C scission to yield CH3 + CH2O and the H-elimination to make H + CH3CHO, were characterized using a high-level coupled-cluster-based composite quantum chemical method (mHEAT-345(QΛ)). The former route is found to be dominant while the latter is insignificant, in agreement with previous experimental and theoretical studies. Thermal rate coefficients are calculated for P = 0.001-658 atm (of air) and T = 300-2500 K using semiclassical transition state theory (SCTST) in combination with a pragmatic two-dimensional E,J-resolved master equation (2DME). The effects of tunneling and anharmonicity on the calculated rate constants are also examined. The tunneling factor is found to be inversely dependent on pressure, contrary to previous observations of pressure-dependent tunneling in entrance channels.

Unified linear response theory of quantum electronic circuits

Modeling the electrical response of multi-level quantum systems at finite frequency has been typically performed in the context of two incomplete paradigms: (i) input-output theory, which is valid at any frequency but neglects dynamic losses, and (ii) semiclassical theory, which captures dynamic dissipation effects well but is only accurate at low frequencies. Here, we develop a unifying theory, valid for arbitrary frequencies, that captures both the small-signal quantum behavior and the non-unitary effects introduced by relaxation and dephasing. The theory allows a multi-level system to be described by a universal small-signal equivalent-circuit model, a resonant RLC circuit, whose topology only depends on the number of energy levels. We apply our model to a double-quantum-dot charge qubit and a Majorana qubit, showing the capability to continuously describe the systems from adiabatic to resonant and from coherent to incoherent, suggesting new and realistic experiments for improved quantum state readout. Our model will facilitate the design of hybrid quantum–classical circuits and the simulation of qubit control and quantum state readout.

First-principles insights into thermoelectric behavior of XNiAs (X = Sc, Y) half-Heusler compounds

Abstract Half-Heusler (HH) compounds are regarded as potential candidates for thermoelectric devices to convert waste heat energy into electrical power, which could help mitigate the ongoing energy crisis. In this study, we investigate the structural, electronic, magnetic, and thermoelectric properties of HH compounds XNiAs (X = Sc, Y) using Density Functional Theory (DFT) and semi-classical Boltzmann transport theory (BTE). The compounds are non-magnetic semiconductors with an indirect band gap of 0.48 ( 0.50) eV for ScNiAs (YNiAs) respectively. Both materials show dynamic and mechanical stability, with ScNiAs displaying brittleness and YNiAs exhibiting ductility. At room temperature, the lattice thermal conductivity (κ l ) for ScNiAs is 28.67 W/mK, while for YNiAs, it is 15.21 W/mK and both decrease as the temperature rises. The highest value of power factors is 29.03 μW/cmK2 and 29.74 μW/cmK2 for ScNiAs and YNiAs respectively at 1100 K for n-type doping. The optimal values of the figure of merit (zT) for n-type doping are 0.33 for ScNiAs and 0.58 for YNiAs at 1100 K. Both compounds exhibit better thermoelectric performance for n-type doping compared to p-type doping. The presence of flat bands and higher κ l limits these materials from achieving higher zT values.

Planar Hall Plateau in magnetic Weyl semimetals

Despite the rapid progress in the study of planar Hall effect (PHE) in recent years, all the previous works only showed that the PHE is connected to local geometric quantities, such as Berry curvature. Here, for the first time, we point out that the PHE in magnetic Weyl semimetals is directly related to a global quantity, namely, the Chern number of the Weyl point. This leads to a remarkable consequence that the PHE observation predicted here is robust against many system details, including the Fermi energy. The main difference between non-magnetic and magnetic Weyl points is that the latter breaks time-reversal symmetry T, thus generally possessing an energy tilt. Via semiclassical Boltzmann theory, we investigate the PHE in generic magnetic Weyl models with energy tilt and arbitrary Chern number. We find that by aligning the magnetic and electric fields in the same direction, the trace of the PHE conductivity contributed by Berry curvature and orbital moment is proportional to the Chern number and the energy tilt of the Weyl points, resulting in a previously undiscovered quantized PHE plateau by varying the Fermi energy. We further confirm the existence of PHE plateaus in a more realistic lattice model without T symmetry. By proposing a new quantized physical quantity, our work not only provides a new tool for extracting the topological character of the Weyl points but also suggests that the interplay between topology and magnetism can give rise to intriguing physics.

Enhancing Thermoelectric Performance of Mg3Sb2 Through Substitutional Doping: Sustainable Energy Solutions via First-Principles Calculations

Mg3Sb2-based materials, part of the Zintl compound family, are known for their low thermal conductivity but face challenges in thermoelectric applications due to their low energy conversion efficiency. This study addressed these limitations through first-principles calculations using the CASTEP module in Materials Studio 8.0, aiming to enhance the thermoelectric performance of Mg3Sb2 via strategic doping. Density functional theory (DFT) calculations were performed to analyze electronic properties, including band structure and density of states (D.O.S.), providing insights into the influence of various dopants. The semiclassical Boltzmann transport theory, implemented in BoltzTrap (version 1.2.5), was used to evaluate key thermoelectric properties such as the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and electronic figure of merit (eZT). The results indicate that doping significantly improved the thermoelectric properties of Mg3Sb2, facilitating a transition from p-type to n-type behavior. Bi doping reduced the band gap from 0.401 eV to 0.144 eV, increasing carrier concentration and mobility, resulting in an electrical conductivity of 1.66 × 106 S/m and an eZT of 0.757. Ge doping increased the Seebeck coefficient to −392.1 μV/K at 300 K and reduced the band gap to 0.09 eV, achieving an electronic ZT of 0.859 with low thermal conductivity (11 W/mK). Si doping enhanced stability and achieved an electrical conductivity of 1.627 × 106 S/m with an electronic thermal conductivity of 11.3 W/mK, improving thermoelectric performance. These findings established the potential of doped Mg3Sb2 as a highly efficient thermoelectric material, paving the way for future research and applications in sustainable energy solutions.

Unveiling half-metallic, thermoelectric and optoelectronic behavior of the new Heusler alloy RbCrZ (Z = Si, Ge): a DFT perspective

Abstract Utilizing the density functional theory (DFT) method, this study aims to predict with precision the structural, elastic, electronic, magnetic, thermoelectric, thermal, and optical properties of two recently discovered half-Heusler alloys, namely RbCrSi and RbCrGe. The exchange and correlation potential are accounted for using the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) and the Tran–Blaha-modified Becke–Johnson exchange potential (TB-mBJ). Through structural analysis, it is observed that both RbCrSi and RbCrGe alloys exhibit energetic stability in a type-3 structure with a ferromagnetic (FM) state. Both alloys exhibit half-metallic properties and integer magnetic moments of 3 μB, following the Slater-Pauli rule. Additionally, elastic calculations confirm their mechanical stability and anisotropic ductile behavior. The quasi-harmonic Debye model (QHDM) is employed for calculating thermodynamic properties, while the BoltzTraP code, based on semi-classical Boltzmann theory (SCBT), is utilized for evaluating thermoelectric properties. Findings reveal that RbCrZ alloys (with Z = Si, Ge) exhibit high figure of merit (ZT) values nearing unity at highest temperature. Consequently, the newfound half-Heusler alloys RbCrSi and RbCrGe hold significant promise for applications in thermoelectricity and spintronic devices. This comprehensive analysis underscores the potential of these alloys in the realm of renewable energy applications.&amp;#xD;

Elucidating Heavy-Atom-Tunneling Kinetics in the Cope Rearrangement of Semibullvalene.

In this work, we characterize the temperature dependence of kinetic properties in heavy atom tunneling reactions by means of molecular dynamics simulations, including nuclear quantum effects (NQEs) via Path Integral theory. To this end, we consider the prototypical Cope rearrangement of semibullvalene. The reaction was studied in the 25-300 K temperature range observing that the inclusion of NQEs modifies the temperature behavior of both free energy barriers and dynamical recrossing factors with respect to classical dynamics. Notably, while in classical simulations the activation free energy shows a very weak temperature dependence, it becomes strongly dependent on temperature when NQEs are included. This temperature behavior shows a transition from a regime where the quantum effects are limited and can mainly be traced back to zero point energy, to a low temperature regime where tunneling plays a dominant role. In this regime, the free energy curve tunnels below the potential energy barrier along the reaction coordinate, allowing much faster reaction rates. Finally, the temperature dependence of the rate constants obtained from molecular dynamics simulations was compared with available experimental data and with semi-classical transition state theory calculations, showing comparable behaviors and similar transition temperatures from thermal to (deep) tunneling regime.

Ab-initio prediction of gigantic anomalous Nernst effect in ferromagnetic monolayer transition metal trihalides

The anomalous Hall conductivity of all transition metal trihalides was explored using first-principles calculations. Employing the Fukui-Hatsugai-Suzuki method, we found that ferromagnetic monolayersXBr3(X= Pd, Pt) possessed the quantized anomalous Hall conductivity (QAHC) with and without carrier doping. Due to unique QAHC, their transverse thermoelectric properties ofXBr3(X= Pd, Pt) were investigated. Employing the semi-classical Boltzmann transport theory, the transverse thermoelectric coefficient of each monolayer was analyzed. Anomalous Nernst coefficients (ANCs) of theXBr3monolayers were prominent both at and near the Fermi level. Under an assumed relaxation time of 10 fs, the maximum ANCs for the PdBr3(PtBr3) monolayer reached -54.1 (-23.3)µV K-1atT=300 K upon doping with 1.21 × 1014(5.64 × 1013) holes cm-2. The large ANCs of theXBr3monolayers were attributed to the opening of a narrow bandgap generated by spin-orbit coupling both at and near the Fermi level, which led to a large Seebeck-induced charge current and large anomalous Nernst conductivity. These results suggest that ferromagneticXBr3monolayers have significant potential for application in thermoelectric devices.

Optical and thermoelectric properties of layer structured Ba2XS4 (X = Zr, Hf) for energy harvesting applications

The main objective of this research is to provide a comprehensive insight into the optical and thermoelectric properties of layer structured Ba2XS4(X = Zr, Hf) for energy harvesting applications using Density Functional Theory (DFT) and semiclassical Boltzmann transport theory. There is a good match between the computed lattice parameters and the available experimental data. Both compounds are thermodynamically and mechanically stable and they are soft, ductile, machinable, and elastically anisotropic. The indirect band gaps are found to be 1.03 eV for Ba2ZrS4 and 1.48 eV for Ba2HfS4. Both compounds possess a mixture of ionic and covalent bonding confirmed by charge density distribution and Mulliken bond population analysis. The maximum absorption is in the ultraviolet regions (∼13.6eV) of light spectra. The total thermal conductivity increases with temperature due to increasing trend of electronic thermal conductivity. The total thermal conductivity at 700 K along c-axis is 4.6 (6.1 W/mK) for Ba2ZrS4 (Ba2HfS4). For p-type Ba2ZrS4 (Ba2HfS4), power factor (PF) is about 7 (5.7) mW/mK2, whereas for n-type it is about 4 (3.9) mW/mK2 at 700 K along c-axis. The power factors of the studied compounds are much higher than those of the reported GeTe and SnSe which would create great interest for further study. The predicted ZT values at 700 K for p-type Ba2ZrS4 and Ba2HfS4 are 0.7 and 0.6, respectively. These values may further be improved through reduction of thermal conductivity and tuning ductility employing known suitable strategies such as alloying and nano-structuring. Finally, Ba2ZrS4 and Ba2HfS4 can be considered new eco-friendly alternatives to previously studied toxic lead-based thermoelectric materials. Their unique advantages of high thermodynamic stability, non-toxic nature and high performance make them strong candidate for sustainable energy solutions.

Enhanced Thermoelectric Performance of Nanostructured 2D Tin Telluride.

A lot of experimental studies are conducted on theoretically predicted thermoelectric 2D materials. Such materials can pave the way for charging ultra-thin electronic devices, self-charging wearable devices, and medical implants. This study systematically explores the thermoelectric attributes of bulk and 2D nanostructured Tin Telluride (SnTe), employing experimental investigations and theoretical analyses based on semiclassical Boltzmann transport theory. The bulk SnTe is synthesized through flame melting, while the 2D SnTe is produced via liquid phase exfoliation. The comprehensive assessment of thermoelectric properties integrated experimental measurements utilizing a Physical Property Measurement System and theoretical calculations from the BoltzTraP code. Experimental thermoelectric studies show a high ZT of 0.17 for 2D SnTe when compared to bulk (0.005) at room temperature. This rise in ZT is due to the high Seebeck coefficient and low thermal conductivity of nanostructured 2D SnTe. Density functional theory (DFT) studies reveal the contribution of the density of states (DOS) and energy bandgap in enhancing the Seebeck coefficient and lowering thermal conductivity by interface scattering.

Atomistic spin dynamics simulations of magnonic spin Seebeck and spin Nernst effects in altermagnets

Magnon band structures in altermagnets are characterized by an energy splitting of modes with opposite chirality, even in the absence of applied external fields and relativistic effects, because of an anisotropy in the Heisenberg exchange interactions. We perform quantitative atomistic spin dynamics simulations based on electronic structure calculations on rutile RuO2, a prototypical “d-wave” altermagnet, to study magnon currents generated by thermal gradients. We report substantial spin Seebeck and spin Nernst effects, i.e., longitudinal or transverse spin currents, depending on the propagation direction of the magnons with respect to the crystal, together with a finite spin accumulation associated with nonlinearities in the temperature profile. Our findings are consistent with the altermagnetic spin-group symmetry, as well as predictions from linear spin-wave theory and semiclassical Boltzmann transport theory. Published by the American Physical Society 2024

Low-Power Threshold Optical Bistability Enabled by Hydrodynamic Kerr Nonlinearity of Free Carriers in Heavily Doped Semiconductors.

We develop an efficient numerical model based on the semiclassical hydrodynamic theory for studying Kerr nonlinearity in degenerate electron systems such as heavily doped semiconductors. This model provides direct access to the electromagnetic responses of the quantum nature of the plasmons in heavily doped semiconductors with complex geometries, which is nontrivial for conventional frameworks. Using this model, we demonstrate nanoscale optical bistability at an exceptionally low-power threshold of 1 mW by leveraging Kerr-type hydrodynamic nonlinearities supported by the heavily doped semiconductor's free carriers. This high nonlinearity is enabled by a strong coupling between metallic gap plasmons and longitudinal bulk plasmons in the semiconductor due to quantum pressure. These findings offer a viable approach to studying Kerr-type nonlinearity and lay the groundwork for developing efficient and ultrafast all-optical nonlinear devices.