Quantum Kinetic Model Research Articles

Sensitivity analysis and uncertainty quantification for a three-dimensional rarefied ionized hypersonic flow

The “communications blackout” phenomenon has bothered the aerospace industry for several decades. However, the unsatisfying numerical methods and the rapidly changing inflow conditions make the estimation of electrons’ density inaccurate. To lay the first step for model calibration and the anti-blackout design, the Artificial Neural Networks and the direct simulation Monte Carlo (DSMC) method with the quantum-kinetic (Q-K) model are brought together to perform the global sensitivity analysis and uncertainty quantification. The three-dimensional RAM-C II (the second flight of the Radio Attenuation Measurement experiments) head flows are simulated considering aleatory uncertainties (inflow uncertainties) and epistemic uncertainties (reaction parameters uncertainties). Under the inflow condition of an 81 km atmosphere and a velocity of 7.8 km/s, aleatory uncertainties are found to be the dominant type of uncertainty for the number density of electrons, especially the freestream velocity, which means the accurate measurement of the vehicle’s velocity is much more critical than the calibration of the model. The importance ranking is listed, and the “Three rules” for finding the essential reactions are proposed. The probability that the real value is smaller than the nominal value considering both uncertainties is 27%–68%.

Atmospheric Degradation Mechanism of Isoamyl Acetate Initiated by OH Radicals and Cl Atoms Revealed by Quantum Chemical Calculations and Kinetic Modeling.

Isoamyl acetate is one of the volatile organic compound class molecules relevant to agricultural and industrial applications. With the growing interest in isoamyl acetate applications in industry, the atmospheric fate of isoamyl acetate must be considered. Reaction mechanisms, potential energy profiles, and rate constants of isoamyl acetate reaction with atmospheric relevant oxidant OH radicals and Cl atoms have been obtained from the quantum chemical calculations and kinetic modeling. The geometry optimizations were conducted using M06-2X/6-311++G(3df,3pd) followed by single point-energy calculations at the DLPNO-CCSD(T) method with an extrapolated complete basis set. The rate constants were calculated by solving the master equation. A hydrogen-abstraction reaction dominates the first step of isoamyl acetate degradation, while the addition-substitution reaction plays a small role in the degradation products. The kinetic study was conducted to evaluate the rate constants within a temperature range of 200-400 K. The total rate constants for the isoamyl acetate degradation reactions initiated by the OH radical and Cl atom were determined to be 6.96 × 10-12 and 1.27 × 10-10 cm3 molecule-1 s-1, respectively, under standard temperature and pressure conditions. The product degradation mechanism, ozone formation potential, and atmospheric impacts were discussed.

Formation of Products of Incomplete Destruction (PID) from the Thermal Oxidative Decomposition of Perfluorooctanoic Acid (PFOA): Measurement, Modeling, and Reaction Pathways.

The thermal decomposition of perfluorooctanoic acid (PFOA) under oxidative conditions was investigated using air (O2) and N2O as oxidants over temperatures ranging from 400 to 1000 °C in an α-alumina reactor. In the presence of air, PFOA was found to decompose into perfluorohept-1-ene (C7F14) and perfluoroheptanoyl fluoride (C7F14O) in addition to HF, CO, and CO2. At temperatures above 800 °C, both C7F14 and C7F14O were no longer detected. A comprehensive analysis of the reaction mechanisms through quantum chemical analysis and kinetic modeling in combination with experimental observations was utilized to identify key reaction pathways. Quantum chemical analysis led to the conclusion that oxygen atoms are crucial in decomposing perfluoroalk-1-enes, especially the stable perfluorohept-1-ene (C7F14). Under oxidative conditions, it was found that significant quantities of C2F6 and CF4 were formed. Further quantum chemical analysis suggests that the O atoms facilitate the formation of volatile fluorinated compounds (VFCs) such as tetrafluoromethane (CF4) and hexafluoroethane (C2F6), particularly at higher temperatures. By elucidating these key reactions, an improved understanding of the potential formation products of incomplete combustion (PICs) or products of incomplete destruction (PIDs) is made.

Zero-dimensional analysis of the effect of water vapor on reducing electrons in the plasma sheath

In this study, an air-water vapor ionization reaction model is developed within the quantum-kinetic (Q–K) model of the direct simulation Monte Carlo method to investigate the detailed mechanism of how water vapor reduces electrons. The zero-dimensional simulations of a typical non-equilibrium flow field downstream of a normal shock are designed, where the electron number density decreases by two orders of magnitude due to water vapor. We conclude that the introduction of water vapor reduces the mole fractions of oxygen atoms and nitrogen atoms through five pairs of reactions and enhances the reverse nitric oxide associative ionization reaction, leading to electron consumption. The phenomena and corresponding mechanisms under varying mole fractions of water vapor, air temperatures, and water vapor temperatures are investigated. Based on the mechanisms, we propose that the addition of hydrogen ions could improve the water's mitigation effect, which is then proven to be able to reduce the electron number density by another two orders of magnitude, not only at high air temperatures but also at lower air temperatures or lower mass injection rates.

Self-consistent quantum-kinetic theory for interacting drifting electrons and force-driven phonons in a 1D system

A self-consistent quantum-kinetic model is developed for studying strong-field nonlinear electron transport interacting with force-driven phonons within a nanowire system. For this model, phonons can be dragged into motion through strong electron–phonon scattering by fast-moving electrons along the opposite direction of the DC electric field. Meanwhile, the DC-field induced charge current of electrons can be either enhanced or reduced by the same electron–phonon scattering, depending on the relative direction of a DC field with respect to that of an applied temperature gradient for driving phonons. By making use of this quantum-kinetic model beyond the relaxation-time approximation, neither electron nor phonon temperature is required for describing ultrafast electron–phonon scattering and their correlated transports in this 1D electronic-lattice system.

Quantum chemical calculation driven insights into deep eutectic solvent‐accelerated photoinduced reversible complexation‐mediated polymerization

AbstractDeep eutectic solvent (DES) is used as both photocatalyst and solvent for photoinduced reversible complexation‐mediated polymerization (photo‐RCMP), which enables a rapid polymerization to produce polymers with predictable molar mass and low molar mass dispersity (Đ). This work illustrates a comprehensive understanding of DES‐accelerated RCMP's mechanism and kinetic features through quantum chemical calculations and kinetic modeling. According to the results, electrons transferring from hydrogen bond in DES to iodine atom in alkyl iodide (RI) initiator under light irradiation lowers the decomposition free energy of complex RI‐DES. This procedure facilitates the generation of primary radicals, thus contributing to the DES‐accelerated phenomenon. In the meantime, the reaction paths are identified by computation as (i) decomposition of RI‐DES under light irradiation generates active radicals and ·I‐DES complex and (ii) combination of two ·I‐DES releases iodine (I2) and regenerates DES. In addition, kinetic modeling based on the method of moments successfully identifies kinetic features of polymerization in the presence and absence of DES, respectively. Kinetic modeling shows a fast increase in primary radicals concentration and rapid build‐up of the photo‐RCMP activation‐deactivation equilibrium, demonstrating that DES is a beneficial photocatalyst and solvent to enable the rapid generation of primary radicals and accelerate the completion of catalytic cycle. This research provides an in‐depth understanding of DES‐involved photo‐RCMP and lays a theoretical foundation for expanding the application of DES to other polymerization systems.

Bulk plasmon-limited mobility in semiconductors: from bulk to nanowires

Analytical expressions are obtained for the low-field mobility in semiconductors for scattering of three-dimensional (3D), two-dimensional (2D), and one-dimensional (1D) charged carriers by bulk plasmons. The consideration is based on the quantum kinetic equation and model distribution function in form of a shifted Fermi distribution and includes calculations of the dielectric function of 3D, 2D and 1D carriers in the random phase approximation. The resulting analytical expressions give dependences of the plasmon limited mobility on the dimensionality of charge carrier system, their density, effective mass, temperature and confining dimensions. The plasmon limited mobility decreases as the dimensionality of the electron gas D decreases. The physical reason for this is an increase in the absolute value of the cutoff vector with a decrease in D. Comparison of our calculations with known experimental data shows that relative contribution of the electron–plasmon scattering to total mobility reaches a maximum in the temperature range 10–100 K and can be a few percent in bulk crystals, ten of percent in quantum wells, and is close to the experimental values in nanowires. A noticeable effect of the scattering 3D, 2D and 1D electrons by bulk plasmons on mobility is expected in semiconductors with a sufficiently high mobility of more than 105 cm2 V−1 s.

Identifying the essential roles of light and sonication in dual‐stimuli regulated bulk atom transfer radical polymerization by multiscale simulation

AbstractMore and more attention has been paid to the important roles of external fields in controlled radical polymerization (CRP). However, their essential roles have not been studied thoroughly yet, which hinders the in‐depth understanding of the mechanism and kinetics. Herein, a strategy combining quantum chemical calculations (QCC) and kinetic modeling was adopted to identify the essential roles of light and ultrasonication in the dual‐stimuli regulated bulk atom transfer radical polymerization (ATRP). At the molecular level, the impact of light on Cu‐catalyzed ATRP was investigated. The CuIIBr/Me6TREN has high absorbance at an experimental wavelength of 365 nm (main excitation S0 → D7 accounts for 84.93%). Electron transfer reactions involving Me6TREN are more favorable paths for photochemical reactions, and the mechanism of the copper activation/deactivation pathway is inner sphere electron transfer. At the micro‐scale, a kinetic model based on the method of moment was established with a “series” encounter pair model to consider the influence of ultrasound on diffusional limitation. Simulation results show that the changes of the reaction rate coefficients ka, kda, and kt at high conversion reflect the degree of diffusional limitation by ultrasound. The multiscale modeling strategy applied in this study identifies the essential roles of photo and ultrasonication in dual‐stimuli regulated model systems, which can be extended to other external‐field regulated CRP to improve the mechanistic understanding.

Anatomy of nanomagnetic switching at a 3D topological insulator PN junction

A P-N junction engineered within a Dirac cone system acts as a gate tunable angular filter based on Klein tunneling. For a 3D topological insulator with a substantial bandgap, such a filter can produce a charge-to-spin conversion due to the dual effects of spin-momentum locking and momentum filtering. We analyze how spins filtered at an in-plane topological insulator PN junction (TIPNJ) interact with a nanomagnet, and argue that the intrinsic charge-to-spin conversion does not translate to an external gain if the nanomagnet also acts as the source contact. Regardless of the nanomagnet’s position, the spin torque generated on the TIPNJ is limited by its surface current density, which in turn is limited by the bulk bandgap. Using quantum kinetic models, we calculated the spatially varying spin potential and quantified the localization of the current versus the applied bias. Additionally, with the magnetodynamic simulation of a soft magnet, we show that the PN junction can offer a critical gate tunability in the switching probability of the nanomagnet, with potential applications in probabilistic neuromorphic computing.

Ponderomotive force due to the intrinsic spin for electrostatic waves in a magnetized plasma

We study the contribution from the electron spin to the ponderomotive force, using a quantum kinetic model, including the spin–orbit correction. Specifically, we derive an analytical expression for the ponderomotive force, applicable for electrostatic waves propagating parallel to an external magnetic field. To evaluate the expression, we focus on the case of Langmuir waves and on the case of the spin resonance wave mode, where the classical and spin contributions to the ponderomotive force are compared. Somewhat surprisingly, depending on the parameter regime, we find that the spin contribution to the ponderomotive force may dominate for the Langmuir wave, whereas the classical contribution can dominate for the spin resonance mode.

In-depth mechanistic and kinetic investigation of sonochemically mediated atom transfer radical polymerization using modeling approach

Mechano/sonochemically mediated reversible deactivation radical polymerization has attracted great attention because of the novel electron transfer regulation process and high-efficient process intensification on mass transfer. Herein, a multi-scale modeling strategy combining quantum chemical calculation and kinetic modeling was developed for sonochemically induced electron transfer controlled atom transfer radical polymerization (SET-ATRP) to study the complicated SET process and its effects on polymerization. At the molecular scale, density functional theory (DFT) calculations were used to acquire the electron characteristic and structure–reactivity of the reactants, intermediates and products during SET process, which provides guideline to figure out the underlying mechanism. Results showed that DMSO•• generated under ultrasonication could react with free Me6TREN to induce electron transfer for the reduction of CuIIBr/L+ to produce CuI/L+, which is the key step for a successful polymerization. The corresponding elementary reaction rate coefficients were calculated by thermodynamic formulae combining transition state theory and Marcus theory. At the micro-scale, kinetic modeling based on method of moment was established to account for the role of SET process in regulating polymerization. Good agreements between the simulation results and experimental data confirmed the reliability of the as-developed multi-scale modeling strategy. More Me6TREN and CuIIBr/L+ resulted in more electron transfer and faster polymerization rate. This work provides an in-depth mechanism insights and kinetic understanding for SET-ATRP, which has a promising potential to promote its progress of application.

Application of Reflected Shock Wave Configuration to Validate Nonequilibrium Models of Reacting Air

The direct simulation Monte Carlo (DSMC) method is used to model transient thermal and chemical relaxation behind reflected shock waves in oxygen–argon and air mixtures under conditions reproducing earlier shock-tube experiments. Two vibration–translation and three popular DSMC chemical reaction models are tested. Where possible, model parameters are adjusted to match equilibrium and nonequilibrium relaxation times and reaction rates. A number of factors that impact relaxation and reaction model validation are examined, including gas–surface interactions, time-varying freestream properties, location of the observation point, electronic excitation, and nonequilibrium populations of vibrational states probed in the experiments. Comparison of numerical and experimental results has demonstrated that the reflected shock configuration is a platform very convenient for validation and analysis of high-temperature chemical reaction models. Computations have shown that the Bias reaction model is superior to the total collision energy and quantum kinetic models, providing reasonable agreement with measured absorbance time histories and vibrational temperatures in oxygen–argon mixtures and pure . There are some modeling-versus-experiment differences observed for air that may warrant additional studies focused on Zeldovich reaction rates and oxygen–nitrogen vibrational excitation and nonequilibrium dissociation rate.

The secondary chemistry of synthetic fuel oxymethylene ethers unraveled: Theoretical and kinetic modeling of methoxymethyl formate and formic anhydride decomposition

Replacing fossil fuels by oxymethylene ethers (OMEs) produced from renewable resources could help to reduce the rising CO2 levels. In this work, the thermal decomposition chemistry of methoxymethyl formate (CH3OCH2OCHO) and formic anhydride (OCHOCHO) is investigated by means of a combination of quantum chemical calculations and kinetic modeling. The latter compounds are two important intermediates formed during the thermal decomposition chemistry of synthetic fuel OMEs. Two detailed kinetic models are developed based on first principles to describe the radical decomposition chemistry of methoxymethyl formate and formic anhydride, which are ultimately incorporated into the OME-2 model from De Ras et al. (Combustion and Flame, 2022). This newly obtained kinetic model describes experimental measurements for pyrolysis from literature significantly better than the model from the original study, without any fitting of thermodynamic or kinetic parameters. More particularly, some minor compounds are now satisfactorily reproduced within the experimental uncertainty margin of 10 mol% relative. Methoxymethyl formate and formic anhydride are found to be more reactive compared to OMEs. Both a reaction pathway analysis and sensitivity analysis reveal the important decomposition pathways under pyrolysis conditions.

Experimental and Theoretical Study on the Enhancement of Alkanolamines on Sulfuric Acid Nucleation.

Alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are extensively used for CO2 capture and consumer products. Despite their prevalence in industrial applications, the fate of alkanolamines in the atmosphere remains relatively unknown. One likely reaction pathway for these chemicals in the atmosphere is new particle formation with sulfuric acid. Here, we present the first experimental results showing the formation of sulfuric acid dimers enhanced by MEA, DEA, and TEA from the measurement of molecular clusters. This study examines the nucleation reactions of MEA, DEA, and TEA with sulfuric acid in a clean, laminar flow reactor. The chemical compositions and concentrations of the freshly nucleated clusters were analyzed using a custom-built atmospheric pressure chemical ionization long time-of-flight mass spectrometer known as the Pittsburgh Cluster CIMS. Quantum chemical calculations and kinetic modeling of sulfuric acid-MEA/DEA/TEA clusters were also performed to determine relative cluster stabilities between these sulfuric acid-base systems. Experimental results indicate that MEA, DEA, and TEA at the part per trillion by volume (pptv) concentrations can enhance sulfuric acid dimer formation rates but to a lesser extent than dimethylamine (DMA). Thus, MEA, DEA, and TEA will potentially play an important role in new particle formation in industrial cities where these alkanolamines are emitted.

Kinetic and Mechanistic Investigations of OH-Initiated Atmospheric Degradation of Methyl Butyl Ketone.

Methyl butyl ketone (MBK, 2-hexanone) is a common atmospheric oxygenated volatile organic compound (OVOC) owing to broad industrial applications, but its atmospheric oxidation mechanism remains poorly understood. Herein, the detailed mechanisms and kinetic properties of MBK oxidation initiated by OH radicals and subsequent transformation of the resulting intermediates are performed by employing quantum chemical and kinetic modeling methods. The calculations show that H-abstraction at the C4 position of MBK is more favorable than those at the other positions, with the total rate coefficient of k(T) = 4.13 × 10-14 exp(1576/T) cm3 molecule-1 s-1 at 273-400 K. The dominant pathway of unimolecular degradation of the C-centered alkyl radical is 1,2-acyl group migration. For the isomerization of the peroxy radical RO2, 1,5- and 1,6-H shifts are more favorable than 1,3- and 1,4-H shifts. The multiconformer rate coefficient kMC-TST of the first H-shift of the RO2 radical is estimated to be 1.40 × 10-3 s-1 at room temperature. Compared to the H-shifts of analogous aliphatic RO2 radicals, it can be concluded that the carbonyl group enhances the H-shift rates by as much as 2-4 orders of magnitude. The rate coefficients of the RO2 radical reaction with the HO2 radical exhibit a weakly negative temperature dependence, and the pseudo-first-order rate constant k'HO2 = kHO2[HO2] is calculated to be 3.32-22.10 × 10-3 s-1 at ambient temperature. The bimolecular reaction of the RO2 radical with NO leads to the formation of 3-oxo-butanal as the main product with the formation concentration of 2.2-7.4 μg/m3 in urban areas. The predicted pseudo-first-order rate constant k'NO = kNO[NO] is 2.20-9.98 s-1 at room temperature. By comparing the kMC-TST, k'HO2, and k'NO, it can be concluded that reaction with NO is the dominant removal pathway for the RO2 radical formed from the OH-initiated oxidation of MBK. These findings are expected to deepen our understanding of the photochemical oxidation of ketones under realistic atmospheric conditions.

Weyl–Wigner description of massless Dirac plasmas: ab initio quantum plasmonics for monolayer graphene

We derive, from first principles and using the Weyl–Wigner formalism, a fully quantum kinetic model describing the dynamics in phase space of Dirac electrons in single-layer graphene. In the limit ℏ → 0, we recover the well-known semiclassical Boltzmann equation, widely used in graphene plasmonics. The polarizability function is calculated and, as a benchmark, we retrieve the result based on the random-phase approximation. By keeping all orders in ℏ, we use the newly derived kinetic equation to construct a fluid model for macroscopic variables written in the pseudospin space. As we show, the novel ℏ-dependent terms can be written as corrections to the average current and pressure tensor. Upon linearization of the fluid equations, we obtain a quantum correction to the plasmon dispersion relation, of order ℏ 2, akin to the Bohm term of quantum plasmas. In addition, the average variables provide a way to examine the value of the effective hydrodynamic mass of the carriers. For the latter, we find a relation in which Drude’s mass is multiplied by the square of a velocity-dependent, Lorentz-like factor, with the speed of light replaced by the Fermi velocity, a feature stemming from the quasi-relativistic nature of the Dirac fermions.

Nonequilibrium Green’s Function Modeling of Trap-Assisted Tunneling in InxGa1−xN /GaN Light-Emitting Diodes

This work presents an investigation of carrier transport in $\mathrm{Ga}\mathrm{N}$-based light-emitting diodes in the subthreshold forward-bias regime where tunneling processes are relevant. A quantum kinetic theory of trap-assisted tunneling is developed within the framework of the nonequilibrium Green's function formalism. Based on fully nonlocal scattering self-energies computed in the self-consistent Born approximation and a multiband description of the electronic structure, the model provides access to spectral quantities, such as the local density of states and the current density, which are essential to understand the nature of the tunneling process. The quantum nonradiative recombination rates can be reproduced by the conventional Shockley-Read-Hall theory, provided that the classical charge is replaced with the correct quantum charge, which means that trap-assisted tunneling can be described with drift-diffusion solvers complemented with appropriate quantum corrections for the calculation of the local density of states. The subthreshold $I$-$V$ characteristics and ideality factors predicted by the quantum kinetic model are in agreement with measurements.

Organic acid-ammonia ion-induced nucleation pathways unveiled by quantum chemical calculation and kinetics modeling: A case study of 3-methyl-1,2,3-butanetricarboxylic acid

Nucleation of organic acids (OAs) and H2SO4 is an important source for new particle formation in the atmosphere. However, it is still unclear whether organic acids can produce nanoparticles independent of H2SO4. In this study, 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) was adopted as a model of OAs. Pathways of clustering from MBTCA, ammonia and ions (NH4+ and NO3−) to form a 1.9 nm nucleus were investigated by quantum chemical calculation and kinetic modeling. Results show recombination of charged clusters/ions plays an essential role in the nucleation processes. Cluster formation rates increase by a factor of 103 when NH3 increases from 2.6 × 108 molecules·cm−3 (under clean conditions) to 2.6 × 1011 molecules·cm−3 (under polluted conditions), as NH3 can stabilize MBTCA clusters and change ion compositions from H3O+ to NH4+. Although the proposed new mechanism cannot compete with H2SO4–NH3–H2O or H2SO4-OA nucleation currently, it may be important in the future with the decline of SO2 concentration.

Atomistic Band-Structure Computation for Investigating Coulomb Dephasing and Impurity Scattering Rates of Electrons in Graphene.

In this paper, by introducing a generalized quantum-kinetic model which is coupled self-consistently with Maxwell and Boltzmann transport equations, we elucidate the significance of using input from first-principles band-structure computations for an accurate description of ultra-fast dephasing and scattering dynamics of electrons in graphene. In particular, we start with the tight-binding model (TBM) for calculating band structures of solid covalent crystals based on localized Wannier orbital functions, where the employed hopping integrals in TBM have been parameterized for various covalent bonds. After that, the general TBM formalism has been applied to graphene to obtain both band structures and wave functions of electrons beyond the regime of effective low-energy theory. As a specific example, these calculated eigenvalues and eigen vectors have been further utilized to compute the Bloch-function form factors and intrinsic Coulomb diagonal-dephasing rates for induced optical coherence of electron-hole pairs in spectral and polarization functions, as well as the energy-relaxation time from extrinsic impurity scattering of electrons for non-equilibrium occupation in band transport.

Light quantum control of persisting Higgs modes in iron-based superconductors

The Higgs mechanism, i.e., spontaneous symmetry breaking of the quantum vacuum, is a cross-disciplinary principle, universal for understanding dark energy, antimatter and quantum materials, from superconductivity to magnetism. Unlike one-band superconductors (SCs), a conceptually distinct Higgs amplitude mode can arise in multi-band, unconventional superconductors via strong interband Coulomb interaction, but is yet to be accessed. Here we discover such hybrid Higgs mode and demonstrate its quantum control by light in iron-based high-temperature SCs. Using terahertz (THz) two-pulse coherent spectroscopy, we observe a tunable amplitude mode coherent oscillation of the complex order parameter from coupled lower and upper bands. The nonlinear dependence of the hybrid Higgs mode on the THz driving fields is distinct from any known SC results: we observe a large reversible modulation of resonance strength, yet with a persisting mode frequency. Together with quantum kinetic modeling of a hybrid Higgs mechanism, distinct from charge-density fluctuations and without invoking phonons or disorder, our result provides compelling evidence for a light-controlled coupling between the electron and hole amplitude modes assisted by strong interband quantum entanglement. Such light-control of Higgs hybridization can be extended to probe many-body entanglement and hidden symmetries in other complex systems.