Quantum Kinetics 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%.

Mechanistic Inside into the Gas-Phase Reaction.

The reaction between and is critical in nighttime atmospheric chemistry. This reaction is believed to occur via two channels: one leading to the formation of HNO3 and the other forming . A long-standing question regarding this reaction is whether this reaction occurs through HNO3 path or or both at a time. Some indirect experiments proposed the HNO3 path as the exclusive path, while some suggested the possibility of both the paths. In the present work, using high-level quantum chemical and kinetics calculations, we have tried to shed light on the mechanism of this reaction. We have incorporated full triple excitation and partial quadratic excitation corrections at the coupled-cluster level for our energetics part, whereas a master equation approach has been employed to obtain the rate constants within 213-400 K. Our investigation suggests that it is only the path through which the reaction takes place.

Neutrino quantum kinetics in a core-collapse supernova

Our understanding of neutrino flavor conversion in the supernova core is still preliminary, despite its likely relevance to the neutrino-driven supernova mechanism. We present multi-angle and multi-energy numerical simulations of neutrino quantum kinetics within a spherically symmetric shell in the proximity of the region of neutrino decoupling. We rely on inputs from a one-dimensional core-collapse supernova model with a mass of 18.6 M ⊙ and find that, at early post-bounce times (t pb ≲ 0.5 s), no crossing is present in the angular distribution of the electron neutrino lepton number and flavor conversion is triggered by slow collective instabilities. Angular crossings appear for t pb ≳ 0.5 s and fast flavor conversion leads to flavor equipartition, with the spectral energy distribution of ν e (ν̅e) and ν x (ν̅ x ) becoming comparable. Notably, flavor equipartition is not a generic outcome of fast flavor conversion, rather it is a consequence of the relatively similar properties of neutrinos of different flavors characterizing the late accretion phase. Artificially tweaking the collision term to introduce an electron lepton number angular crossing for t pb ≲ 0.5 s, we observe that flavor equipartition is not achieved. While our findings are restricted to a specific supernova model, and they only take into account the feedback of the neutrino background on the flavor conversion, they suggest a rich phenomenology in the supernova core as a function of the post-bounce time which needs to be further explored to assess its impact on the explosion mechanism.

(Keynote) Unified Quantum Theory of Electrochemical Kinetics Based on Coupled Ion-Electron Transfer

A general theory of coupled ion–electron transfer (CIET) is presented, which unifies quantum kinetics of electron transfer (ET) with classical kinetics of bond-breaking ion transfer (IT) in a general framework of non-equilibrium thermodynamics [1]. In the limit of large reorganization energy, the theory predicts Marcus kinetics of “electron-coupled ion transfer” (ECIT). In the limit of large ion-transfer energies, the theory predicts generalized Butler–Volmer kinetics of “ion-coupled electron transfer” (ICET), where the charge transfer coefficient and exchange current are connected to microscopic properties of the electrode/electrolyte interface. In the ICET regime, the reductive and oxidative branches of Tafel’s law are predicted to hold over a wide but finite range of overpotentials, bounded by the ion-transfer energies for oxidation and reduction, respectively. The probability distribution of transferring electron energies in CIET smoothly interpolates between a shifted Gaussian distribution for ECIT (as in the Gerischer–Marcus theory of ET) to an asymmetric, fat-tailed Meixner distribution centered at the Fermi level for ICET. The latter may help interpret asymmetric line shapes in x-ray photo-electron spectroscopy (XPS) and Auger electron spectroscopy (AES) for oxidized metal surfaces in terms of shake-up relaxation of the ionized atom and its image polaron by ICET. In the limit of large overpotentials, the theory predicts a transition to inverted Marcus ECIT, leading to a universal reaction-limited current for metal electrodes, dominated by barrierless quantum transitions. Uniformly valid, closed-form asymptotic approximations are derived that smoothly transition between the limiting rate expressions for ICET and ECIT for metal electrodes, using simple but accurate mathematical functions. The theory is applied to lithium intercalation in lithium iron phosphate (LFP) and found to provide a consistent description of the observed current dependence on overpotential, temperature and concentration, learned from x-ray images [2]. CIET theory thus provides a critical bridge between quantum electrochemistry and electrochemical engineering.[1] M. Z. Bazant, Unified quantum theory of electrochemical kinetics by coupled ion-electron transfer, Faraday Discussions 246, 60-124 (2023).[2] H. Zhao, H. D. Deng, A. E. Cohen, J. Lim, Y. Li, D. Fraggedakis, B. Jiang, B. D. Storey, W. C. Chueh, R. D. Braatz, and M. Z. Bazant, Learning heterogeneous reaction kinetics from X-ray movies pixel-by-pixel, Nature 621, 289-294 (2023). Figure 1

Multipolar condensates and multipolar Josephson effects

When single-particle dynamics are suppressed in certain strongly correlated systems, dipoles arise as elementary carriers of quantum kinetics. These dipoles can further condense, providing physicists with a rich realm to study fracton phases of matter. Whereas recent theoretical discoveries have shown that an unconventional lattice model may host a dipole condensate as the ground state, we show that dipole condensates prevail in bosonic systems due to a self-proximity effect. Our findings allow experimentalists to manipulate the phase of a dipole condensate and deliver dipolar Josephson effects, where supercurrents of dipoles arise in the absence of particle flows. The self-proximity effects can also be utilized to produce a generic multipolar condensate. The kinetics of the n-th order multipoles unavoidably creates a condensate of the (n + 1)-th order multipoles, forming a hierarchy of multipolar condensates that will offer physicists a whole new class of macroscopic quantum phenomena.

Bhatnagar-Gross-Krook subgrid model for neutrino quantum kinetics

Bhatnagar-Gross-Krook subgrid model for neutrino quantum kinetics

Multi-generation oxidation mechanism of M-xylene: Unexpected implications for secondary organic aerosol formation

Secondary organic aerosol (SOA) affects air quality, human health and climate. The multi-generation reactions of volatile organic compounds (VOCs) have become key process for explaining the SOA formation. M-xylene, as one of the most important VOCs in urban atmosphere, has got extensive study. However, the reaction mechanism of the first-generation products hydroperoxides (M-ROOH) and organonitrates (M-RONO2) remain unknown. In this work, the hydroxyl radicals (·OH) initiated reactions of M-ROOH and M-RONO2 were investigated by employing quantum chemical methods and kinetics modeling. The results show that new ring-retaining epoxides, a range of dialdehydes and less volatile hydroperoxides and organonitrates are formed, contributing to SOA formation. By adopting the unveiled new mechanism into the SOSAA box modeling, we found that the yield of SOA from m-xylene oxidation is up to 38%, which is comparable to the experimental value (36%). This work advances current understanding of multi-generation chemistry and elucidates the role of aromatic hydrocarbons oxidation in the formation of SOA.

Numerical modeling of non-equilibrium neutrino radiation field by solving quantum kinetic equation

Numerical modeling of neutrino quantum kinetics is a new frontier in the study of core-collapse supernova (CCSN) and binary neutron star merger (BNSM). The noticeable feature in the quantum kinetics is neutrino flavor conversion driven by neutrino self-interactions. Although there remain many unresolved issues in their non-linear properties of flavor conversions, rapid progress has been made in the last few years. In this article, we introduce the current status for the study of collective neutrino oscillations, which are representative characteristics in self-induced flavor conversions, and then we show our recent results: global quantum kinetic simulations in CCSN and BNSM environments.

Organosulfate produced from consumption of SO3 speeds up sulfuric acid–dimethylamine atmospheric nucleation

Abstract. Although sulfuric acid (SA) and dimethylamine (DMA)-driven nucleation mainly dominates the new particle formation (NPF) process in the atmosphere, seeking the involvement of other gaseous species remains crucial for a better understanding of the NPF. Organosulfate has been detected in the gas phase and abundantly in atmospheric fine particles. However, its molecular formation mechanism and its impact on the NPF are still much less understood. Here, we explored the gas-phase reaction of glycolic acid (GA) with SO3 and evaluated the enhancing potential of its products on the SA–DMA-driven NPF using a combination of quantum chemical calculations and kinetics modeling. We found that the considerable concentration of glycolic acid sulfate (GAS) is thermodynamically accessible from the reaction of GA with SO3, efficiently catalyzed by SA or H2O molecules. The produced GAS can form stable clusters with SA and DMA and speeds up the nucleation rate of the SA–DMA system obviously. Notably, the enhancement by GAS in the SA–DMA-based particle formation rate can be up to ∼ 800 times in the region where the concentration of SA is about 104 molec. cm−3. Supported by observations of atmospheric NPF events at Mt. Tai in China, our proposed ternary GAS–SA–DMA nucleation mechanism further indicates that the organosulfates produced from the consumption of SO3 may play an important role in the unexpected high NPF rates observed in areas with relatively low concentrations of SA. The presented reaction and nucleation mechanisms provide a new feasible source of organosulfates in atmospheric new particles. Based on our findings, the impact of organosulfates on the atmospheric NPF in multiple regions around the world was estimated and discussed.

About the quantum‐kinetic derivation of boundary conditions for quasiparticle Boltzmann equations at interfaces

AbstractQuite a many electron transport problems in condensed matter physics are analyzed with a quasiparticle Boltzmann equation. For sufficiently slowly varying weak external potentials it can be derived from the basic equations of quantum kinetics, provided quasiparticles can be defined and lead to a pole in the quantum‐mechanical propagators. The derivation breaks down, however, in the vicinity of an interface which constitutes an abrupt strong perturbation of the system. In this contribution we discuss in a tutorial manner a particular technique to systematically derive, for a planar, nonideal interface, matching conditions for the quasi‐particle Boltzmann equation. The technique is based on pseudizing the transport problem by two auxiliary interface‐free systems and matching Green functions at the interface. Provided quasiparticles exist in the auxiliary systems, the framework can be put onto the semiclassical level and the desired boundary conditions result. For ideal interfaces, the conditions can be guessed from flux conservation, but for complex interfaces this is no longer the case. The technique presented in this work is geared toward such interfaces.

Quantum chemistry and kinetics of hydrogen sulphide oxidation.

A fundamental understanding of the acid gas (H2S and CO2) chemistry is key to efficiently implement the desulphurisation process and even the production of clean fuels such as hydrogen or syngas. In this work, we developed a new kinetic model for the pyrolysis and oxidation of hydrogen sulphide by merging two previously reported models with the goal of covering a wider range of conditions and including the effect of carbon dioxide. The resulting model, which consists of 75 species and 514 reactions, was used to conduct rate of production and sensitivity analysis in plug flow reactor simulations, and the results were used to determine the most prominent reactions in which hydrogen sulphide, molecular hydrogen, and sulphur monoxide are involved. The resulting list of important reactions was screened and the kinetics of three of them, i.e., SO2 + S2 → S2O + SO, S2O + S2 → S3 + SO, and SO + SH → S2 + OH, was found to warrant further investigation. With the goal of improving the accurancy of our new kinetic model, we carried out a robust quantum chemistry and Rice-Ramsperger-Kassel-Marcus master equation study to obtain, for the first time, the forward and reverse rate constants for those three reactions at temperatures and pressures of interest for combustion and atmospheric chemistry. This work is the first step of a kinetic study that is aimed at improving the understanding of the chemistry of the pyrolysis and oxidation of H2S, highlighting the importance of sulphur-sulphur interactions and providing a fundamental basis for future kinetic models of H2S not only in the field of combustion, but also in atmospheric chemistry.

Toluidine blue O photosensitizer combined with caffeic acid improves antibacterial performance by increasing the permeability of cell membrane

Photodynamic therapy has always been an antibacterial tool for solving multi-drug resistant bacteria problem, but the side effects and the low efficiency due to the high aggregation and low solubility of photosensitizers limit its application. Due to the anti-inflammatory effect of caffeic acid, two novel photosensitizers (CA-1-TBO, CA-TBO) were synthesized by conjugating caffeic acid with toluidine blue O (TBO). The structures have been characterized by 1HNMR and high-resolution mass spectrometry. The UV-vis absorption, fluorescence spectra and the octanol-water partition coefficient of two photosensitizers were measured to evaluate their photophysical properties and hydrophilic/hydrophobic properties. Compared with parent TBO, the two modified photosensitizers have shown a higher quantum yield and kinetics constants of singlet oxygen, which has been supported by the simulation results of density functional theory. As drug-resistant representatives of gram-positive and gram-negative bacteria, respectively, S. aureus and P. aeruginosa have been used for in vitro antibacterial experiments. The sterilization efficiencies of the two modified photosensitizers far exceed that of parent TBO. The results of the octanol-water partition coefficient and fluorescence quantification showed that modified photosensitizers CA-1-TBO and CA-TBO could be more accumulated than parent TBO. Based on scanning electron microscopy images, protein gel electrophoresis, and the conductivity of the bacterial solution, the possible mechanism of improved antibacterial photodynamic efficiencies could be induced by membrane permeability due to the caffeic acid effect. The findings demonstrate the significant potential of natural phenolic compounds in the development of photosensitizer molecules with characteristics such as more efficient, biocompatible and less side effects.

Vibrational Dichroism of Chiral Valley Phonons.

Valley degrees of freedom in transition metal dichalcogenides thoroughly influence electron-phonon coupling and its nonequilibrium dynamics. We conducted a first-principles study of the quantum kinetics of chiral phonons following valley-selective carrier excitation with circularly polarized light. Our numerical investigations treat the ultrafast dynamics of electrons and phonons on equal footing within a parameter-free ab initio framework. We report the emergence of valley-polarized phonon populations in monolayer MoS2 that can be selectively excited at either the K or K' valleys depending on the light helicity. The resulting vibrational state is characterized by a distinctive chirality, which lifts time-reversal symmetry of the lattice on transient time scales. We show that chiral valley phonons can further lead to fingerprints of vibrational dichroism detectable by ultrafast diffuse scattering and persist beyond 10 ps. The valley polarization of nonequilibrium phonon populations could be exploited as an information carrier, thereby extending the paradigm of valleytronics to the domain of vibrational excitations.

Semiclassical kinetic theory for systems with non-trivial quantum geometry and the expectation value of physical quantities

Starting from the Keldysh theory, for a general low-energy N-band Hamiltonian in the clean limit, we perform a manifestly gauge-invariant semiclassical expansion. A generalized Berry curvature tensor is shown to control a redistribution of spectral weights. New expressions for certain physical quantities ensue, establishing the limits of a previously proposed correction to the density of states. In the two-band case, we derive a completely general semiclassical kinetic theory including all quantum corrections. As an application, we show how one can recover, out of a single simple calculation, the chiral anomaly, intrinsic anomalous Hall conductivity and chiral magnetic effect, in all generality. The demonstrated flexibility and efficiency of our formalism derives from the insulation it provides from the underlying complexity of the quantum kinetics, notwithstanding its rigorous connection to this deeper level.

A quantum chemical and kinetics study on the unimolecular reactions of fuel radicals formed during the oxidation of n‐propylamine

AbstractThe major intermediate product under co‐combustion conditions of hydrocarbon fuels with ammonia are amines. Herein, we have theoretically investigated the unimolecular reactions of fuel radicals formed during the oxidation of n‐propylamine. Quantum chemical calculations were performed to obtain the optimized structures and vibrational frequencies of reactants, products, and transition states at the B3LYP/aug‐cc‐pVTZ theory level. CCSD(T) single point energy calculations with the basis sets of aug‐cc‐pVDZ and aug‐cc‐pVTZ were further performed against the optimized structures, and the energies were extrapolated into infinite basis limit. Pressure‐dependent rate constants were calculated using Rice–Ramsperger–Kassel–Marcus/master equation analysis. The major reaction pathways for the fuel radicals were found to be β‐scission reactions at CC or CN bonds, and minor pathways were internal hydrogen shift and β‐scission reactions at CH or NH bonds. The calculated reaction rate constant trends were attributed to the decrease in CC and CN bond dissociation energies due to substitution effects from the amino group.

Quantum kinetics of quenched two-dimensional Bose superfluids

We study theoretically the nonequilibrium dynamics of a two-dimensional (2D) uniform Bose superfluid following a quantum quench, from its short-time (prethermal) coherent dynamics to its long-time thermalization. Using a quantum hydrodynamic description combined with a Keldysh field formalism, we derive quantum kinetic equations for the low-energy phononic excitations of the system and characterize both their normal and anomalous momentum distributions. We apply this formalism to the interaction quench of a 2D Bose gas and study the ensuing dynamics of its quantum structure factor and coherence function, both recently measured experimentally. Our results indicate that, in two dimensions, a description in terms of independent quasiparticles becomes quickly inaccurate and should be systematically questioned when dealing with nonequilibrium scenarios.

Photocurrent as a multiphysics diagnostic of quantum materials

The photoexcitation life cycle from incident photon (and creation of photoexcited electron–hole pair) to ultimate extraction of electrical current is a complex multiphysics process spanning across a range of spatiotemporal scales of quantum materials. Photocurrent is sensitive to a myriad of physical processes across these spatiotemporal scales, and over the past decade it has emerged as a versatile probe of electronic states, Bloch band quantum geometry, quantum kinetic processes and device characteristics of quantum materials. This Technical Review outlines the key multiphysics principles of photocurrent diagnostics, for resolving band structure and characterizing topological materials, for disentangling distinct types of carrier scattering that can range from femtosecond to nanosecond timescales and for enabling new types of remote-sensing protocols and photocurrent nanoscopy. These distinctive capabilities underscore photocurrent diagnostics as a novel multiphysics probe for a growing class of quantum materials with properties governed by physics spanning multiple spatiotemporal scales. Photocurrent can be used to reveal the out-of-equilibrium properties of quantum materials over a range of spatiotemporal scales. This Technical Review outlines the principles of photocurrent diagnostics and how it can be used to probe electronic states, quantum geometry and quantum kinetics of materials.

Post-reaction internal energy distributions of quantum-kinetics model for simulating chemical reactions of polyatomic molecules

Chemical reactions significantly influence aerodynamic performance during spacecraft entry into the Martian atmosphere. Several chemical reaction models have been proposed in the direct simulation Monte Carlo simulation. The quantum-kinetics (Q-K) model has been applied in the case of diatomic molecules. Given that the Martian atmosphere consists primarily of CO2, it is crucial to find ways of implementing the Q-K model for polyatomic molecules. Although the chemical reaction rates involving CO2 have been investigated using the Q-K model, the problem of achieving detailed balance remains. Multiple vibrational modes exist for polyatomic molecules. Under the Q-K distribution, the average vibrational level of each mode is higher than that under the equilibrium distribution, and the total energy may be insufficient. Hence, its applicability to polyatomic molecules needs to be revealed. In this study, a comparison is made of the respective results obtained using the Larsen–Borgnakke (L–B) and Q-K distribution methods for the energy distribution of the reaction CO2+O⇋CO+O2, and the detailed balance is achieved with the Q-K method but not the L–B method. Under the conditions assumed in this study, the vibrational energy distribution of CO consumed by the reverse reaction is not in good agreement with that generated by the forward reaction, leading to the failure of the L–B method. Finally, the results indicate that the detailed balance is reached only when the collision temperature, based on the translational and vibrational energy, is employed to adjust the activation energy rather than the translational temperature generally adopted in the literature.

Effect of (H2O)n (n = 1 and 2) on HOCl + Cl reaction.

In the present work, we investigate the effect of water molecules (H2O and (H2O)2) on HOCl + Cl˙ → ClO˙ + HCl (R1), and HOCl + Cl˙ → OH˙ + Cl2 (R2) reactions using quantum chemical and kinetics calculations. The present investigation suggests that a water molecule decreases the energy barrier of both reactions significantly, compared to uncatalyzed reaction. However, the effective rate constants for the water catalyzed path for both channels (R1 and R2) were found to be lower than the bimolecular rate constant of the uncatalyzed path. Further, it was found that the R2 reaction will dominate over the R1 reaction, with or without catalyst. Interestingly, the uncatalyzed title reaction was found to be two times faster than the HOCl + OH˙ reaction, but in the presence of water, HOCl + OH˙ becomes the dominant reaction compared to the HOCl + Cl˙ reaction in the atmosphere. In addition, the concentration of bimolecular complexes formed in the presence of a catalyst are found to be higher than the precursor molecule of the uncatalyzed reaction, which suggests that in the presence of catalyst, the HOCl + Cl˙ reaction would favor the catalyzed path rather than the uncatalyzed path.

Oligomer formation from the gas-phase reactions of Criegee intermediates with hydroperoxide esters: mechanism and kinetics

Abstract. Hydroperoxide esters, formed in the reactions of carbonyl oxides (also called Criegee intermediates, CIs) with formic acid, play a crucial role in the formation of secondary organic aerosol (SOA) in the atmosphere. However, the transformation mechanism of hydroperoxide esters in the presence of stabilized Criegee intermediates (SCIs) is not well understood. Herein, the oligomerization reaction mechanisms and kinetics of distinct SCI (CH2OO, syn-CH3CHOO, anti-CH3CHOO, and (CH3)2COO) reactions, with their respective hydroperoxide esters and with hydroperoxymethyl formate (HPMF), are investigated in the gas phase using quantum chemical and kinetics modeling methods. The calculations show that the addition reactions of SCIs with hydroperoxide esters proceed through successive insertion of SCIs into hydroperoxide ester to form oligomers that involve SCIs as the repeated chain unit. The saturated vapor pressure and saturated concentration of the formed oligomers decrease monotonically as the number of SCIs is increased. The exothermicity of oligomerization reactions decreases significantly when the number of methyl substituents increases, and the exothermicity of anti-methyl substituted carbonyl oxides is obviously higher than that of syn-methyl substituted carbonyl oxides. The −OOH insertion reaction is energetically more feasible than the −CH insertion pathway in the SCI oligomerization reactions, and the barrier heights increase with increasing the number of SCIs added to the oligomer, except for syn-CH3CHOO. For the reactions of distinct SCIs with HPMF, the barrier of the −OOH insertion pathway shows a dramatic decrease when a methyl substituent occurs at the anti-position, while it reveals a significant increase when a methyl group is introduced at the syn-position and dimethyl substituent. Compared with the rate coefficients of the CH2OO + HPMF reaction, the rate coefficients increase by about 1 order of magnitude when a methyl substituent occurs at the anti-position, whereas the rate coefficients decrease by 1–2 orders of magnitude when a methyl group is introduced at the syn-position. These new findings advance our current understanding of the influence of Criegee chemistry on the formation and growth processes and the chemical compositions of SOA.