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Energy decomposition analysis method with the DFT-in-xTB embedding strategy for intermolecular interactions in large systems
In this work, an energy decomposition analysis (EDA) method, termed DM-EDA(EB), is introduced to explore intermolecular interactions in large systems by employing a DFT-in-xTB embedding scheme. DM-EDA(EB) integrates density matrix-based EDA (DM-EDA) with the GFNn-xTB method to decompose the total interaction energy into electrostatic, exchange–repulsion, polarization, and correlation terms. Test cases demonstrate that DM-EDA(EB) can accurately analyze total interaction energies in large systems with the computational efficiency comparable to GFNn-xTB. Notably, by using the appropriate partition strategy, DM-EDA(EB) is able to provide quantificational knowledge of individual interactions in large assemblies.
Simulating many-body open quantum systems by harnessing the power of artificial intelligence and quantum computing
Simulating many-body open quantum systems (OQSs) is challenging due to the intricate interplay between the system and its environment, resulting in strong quantum correlations in both space and time. This Perspective presents an overview of recently developed theoretical methods using artificial intelligence (AI) and quantum computing (QC) to simulate the dynamics of these systems. We briefly introduce the dissipaton-embedded quantum master equation in second quantization, which provides a single master equation suitable for representation by neural quantum states or quantum circuits. The promising performance of AI- and QC-based approaches is demonstrated through preliminary research on simulating the quantum dissipative dynamics of many-body OQSs. We also discuss the limitations and future developments of these methods, which hold promise for overcoming the computational challenges associated with many-body OQS dynamics.
Non-equilibrium coexistence between a fluid and a hotter or colder crystal of granular hard disks
Non-equilibrium phase coexistence is commonly observed in both biological and artificial systems, yet understanding it remains a significant challenge. Unlike equilibrium systems, where free energy provides a unifying framework, the absence of such a quantity in non-equilibrium settings complicates their theoretical understanding. Granular materials, driven out of equilibrium by energy dissipation during collisions, serve as an ideal platform to investigate these systems, offering insights into the parallels and distinctions between equilibrium and non-equilibrium phase behavior. For example, the coexisting dense phase is typically colder than the dilute phase, a result usually attributed to greater dissipation in denser regions. In this article, we demonstrate that this is not always the case. Using a simple numerical granular model, we show that a hot solid and a cold liquid can coexist in granular systems. This counterintuitive phenomenon arises because the collision frequency can be lower in the solid phase than in the liquid phase, consistent with equilibrium results for hard-disk systems. We further demonstrate that kinetic theory can be extended to accurately predict phase temperatures even at very high packing fractions, including within the solid phase. Our results highlight the importance of collisional dynamics and energy exchange in determining phase behavior in granular materials, offering new insights into non-equilibrium phase coexistence and the complex physics underlying granular systems.
Adsorption behavior analysis of CNCl on transition metal-doped fluorinated diamanes: A first-principles study
Cyanogen chloride (CNCl) is a toxic chemical that poses significant risks to human health and the environment; therefore, its level must be accurately monitored. Herein, the adsorption of CNCl by transition metal-doped fluorinated diamanes (F-diamanes) has been extensively studied via first-principles calculations. Key parameters such as adsorption energies, charge transfer amounts, bandgaps, sensitivity, densities of states, projected density of states, charge density differences, and recovery time were systematically analyzed. Results reveal that monometallic doping significantly enhances CNCl adsorption, with increases in adsorption energy by 164%–368% and charge transfer by 1234%–1571%, particularly in the AuFD-CNCl, AgFD-CNCl, and CuFD-CNCl systems, which demonstrated improved sensing performances. Similarly, bimetallic co-doping further strengthened adsorption, with energy enhancements of 277%–309% and charge transfer increases of 1238%–1505%. Au-CuFD-CNCl, Au-AgFD-CNCl, and Cu-AgFD-CNCl systems also showed superior sensing performances. Meanwhile, the recovery time of CNCl molecules on the AuFD, AgFD, Au-CuFD, and Au-AgFD surfaces was drastically reduced to acceptable levels at 279–412 K, leading to their desorption. Therefore, these four systems exhibited excellent reversibility properties, suggesting their applicability in gas-sensing applications. This work can facilitate the applications of doped F-diamanes in environmental conservation, energy storage, and chemical engineering.
Challenges in determining the thermal conductivity of core–shell nanowires by atomistic simulation
In the present work, we investigate the thermal conductivity (κ) of different core–shell nanowires using molecular dynamics simulation and Green–Kubo (EMD), imposing a temperature gradient (NEMD) and Müller-Plathe (rNEMD) approaches. We show that in GaAs@InAs nanowires, the interface effect becomes more significant than the nanowire cross-sectional geometry. In particular, κ decreases as the interface area increases, reaching a minimum, and then increases when the interface strain relaxes. This is particularly important for thermoelectric applications, where minimization of κ is desired. In particular, the different methods can predict minima at different core diameters without special considerations. In addition, the NEMD approach and, to a lesser extent, rNEMD tend to overestimate the κ values, which cannot be corrected with the methods available in the literature. By analyzing the temperature and length dependence, (I) we show that interfacial scattering primarily involves phonon–phonon interactions, which mainly affect low-energy modes, a mechanism that effectively reduces κ at low temperatures. (II) The Langevin thermostat tends to pump low-energy modes in the NEMD approach, but this effect decreases with longer nanowires. (III) Energy exchanges in rNEMD stimulate high-energy phonons, derived from the saturation of κ at a much shorter nanowire length than NEMD. These findings highlight the challenges of accurately determining κ of ultrathin core–shell nanowires, where only the EMD approach provides precise results. With the recognition of non-equilibrium contributions to the overestimation of κ by NEMD and rNEMD, these methods can still provide valuable insights for a comprehensive understanding of the underlying thermal transport mechanisms.
Polariton-induced Purcell effects via a reduced semiclassical electrodynamics approach
Recent experiments have demonstrated that polariton formation provides a novel strategy for modifying local molecular processes when a large ensemble of molecules is confined within an optical cavity. Herein, a numerical strategy based on coupled Maxwell–Schrödinger equations is examined for simulating local molecular processes in a realistic cavity structure under collective strong coupling. In this approach, only a few molecules, referred to as quantum impurities, are treated quantum mechanically, while the remaining macroscopic molecular layer and the cavity structure are modeled using dielectric functions. When a single electronic two-level system embedded in a Lorentz medium is confined in a two-dimensional Bragg resonator, our numerical simulations reveal a polariton-induced Purcell effect: the radiative decay rate of the quantum impurity is significantly enhanced by the cavity when the impurity frequency matches the polariton frequency, while the rate can sometimes be greatly suppressed when the impurity is near resonance with the bulk molecules forming strong coupling. In addition, this approach demonstrates that the cavity absorption of light exhibits Rabi-splitting-dependent suppression due to the inclusion of a realistic cavity structure. Our simulations also identify a fundamental limitation of this approach—an inaccurate description of polariton dephasing rates into dark modes. This arises because the dark-mode degrees of freedom are not explicitly included when most molecules are modeled using simple dielectric functions. As the polariton-induced Purcell effect alters molecular radiative decay differently from the Purcell effect under weak coupling, this polariton-induced effect may facilitate understanding the origin of polariton-modified photochemistry under electronic strong coupling.
A molecular beam study of olefin adsorption on ultrathin ionic liquid films on Pt(111)
We investigate fundamental aspects concerning selectivity in hydrogenation reactions for Solid Catalyst with Ionic Liquid Layer (SCILL)-type systems. Some of us recently reported that the adsorption behavior of 1,3-butadiene and 1-butene on Pt(111) can be tuned with ultrathin layers of the ionic liquid (IL) 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([C1C1Im][Tf2N]): Increasing the IL coverage leads to increased blocking of olefin adsorption sites. Notably, a smaller IL amount is needed to prevent 1-butene adsorption as compared to 1,3-butadiene adsorption, leading to a selectivity window, in which 1,3-butadiene still can be adsorbed while 1-butene cannot. With the aim to evaluate whether this is a general behavior, we study an IL with a longer alkyl chain at the cation, 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide ([C8C1Im][Tf2N]), and an IL with a different anion, 1-methyl-3-octylimidazolium hexafluorophosphate ([C8C1Im][PF6]). Indeed, we observe a selectivity window for all ILs and thus demonstrate that this concept also applies for other ILs with different chain lengths and anions. Nevertheless, there are pronounced differences for the three ILs in terms of the IL coverages required for full blocking and the width of the selectivity window. Different explanations are discussed, e.g., the structure of the IL layer and the interaction strengths of olefins and ILs with the substrate.
Thermal conductivity of the layered titanate K0.8Li0.27Ti1.73O4 explored by a deep learning interatomic potential
The theoretical prediction of thermal conductivity in many layered oxides remains challenging, primarily due to their structural complexity and low symmetry. The traditional Boltzmann transport equation method is highly accurate but limited by the low-order phonon scattering model, which makes it difficult to resolve the high-order scattering effects of low symmetry layered materials. The classical molecular dynamics calculation is efficient but lacks accuracy due to the missing multi-component potential function. In this study, we develop a strategy to predict the thermal conductivity of K0.8Li0.27Ti1.73O4 (KLTO), a model of layered oxides by machine-learning using a deep neural network model to acquire the interatomic potential of KLTO. The deep learning potential (DLP) is in excellent agreement with density functional theory in predicting atomic force, energy, and elastic properties. In addition, the calculated out-of-plane thermal conductivity values based on the DLP (0.37 W m−1 K−1) are close to experimental results (0.28 W m−1 K−1). This machine-learning framework for constructing interatomic potentials can be extended to other layered materials, offering a promising approach for advancing the theoretical study of such systems.
A molecular dynamics study on coalescence-induced jumping of moving and static droplets
In this paper, molecular dynamics simulations are employed to investigate the coalescence-induced jumping behavior of moving and stationary droplets at the nanoscale on superhydrophobic surfaces. The results show that the initial velocity of the droplets significantly influences the coalescence time and jumping characteristics. As the initial velocity increases, the coalescence time decreases, and the horizontal velocity increases, suggesting that controlling the initial velocity can adjust droplet motion behavior. In terms of energy conversion, the total energy conversion rate remains relatively constant at lower initial velocities but increases significantly as the velocity rises. This is primarily due to the reduced coalescence time and viscous dissipation caused by the increased initial kinetic energy, allowing more energy to be converted into the kinetic energy of jumping. The energy conversion rate in the horizontal direction increases with initial velocity, while in the vertical direction, it tends to decrease. This study deepens the understanding of coalescence-induced jumping phenomena at the nanoscale and provides a theoretical basis for engineering applications, showing that droplet behavior can be effectively modulated by controlling the initial velocity.
Structural and dynamical properties of aqueous NaCl brines confined in kaolinite nanopores
Quantifying thermodynamics, structural, and dynamical properties of brine confined in clay pores is critical for a variety of geo-energy applications, including underground hydrogen storage (UHS) and carbon capture and sequestration (CCS). Atomistic molecular dynamics simulations are applied here to study aqueous NaCl brines within 10-Å kaolinite slit pores. NaCl concentrations are chosen at 5, 10, 12.5, and 15 wt. %, all below the solubility limit and high enough to provide statistically relevant information. The distribution of the ions within the nanopores is found not to be homogeneous. Explicitly, Na+ cations, preferentially attracted to the siloxane surface, accumulate in regions with low water density, whereas Cl− anions, attracted to the gibbsite surface of kaolinite, are found within the hydration layers. Confinement affects the properties of ions, with ion pairing being more pronounced within the pore than in bulk aqueous solutions at similar temperatures, pressures, and compositions. Conversely, the ions affect the properties of confined water. For example, the lifetime of water–water hydrogen bonds in confinement is shortened within the hydration shells; increasing salinity from 5 to 12.5 wt. % reduces the likelihood of water density fluctuations near the kaolinite surfaces, although when the NaCl concentration rises from 12.5 to 15 wt. %, Cl− anions enhance the likelihood of density fluctuations for the hydration layer near the gibbsite surface. The simulated molecular trajectories are studied further to extract diffusion coefficients. While confinement in the kaolinite nanopore reduces the mobility of all species, non-monotonic trends are observed as a function of salt concentration. The trends seem associated with the likelihood of ion pairing. Furthermore, the diffusion coefficients for the cations are predicted to be higher than those for the anions, which is contrary to what is typically observed in bulk brines. Because density fluctuations are correlated with properties such as the solubility of gases in confined water, our observations may have important implications for geo-energy applications such as UHS and CCS.
Real-time propagation of adaptive sampling selected configuration interaction wave functions
We have developed a new time propagation method, time-dependent adaptive sampling configuration interaction (TD-ASCI), to describe the dynamics of a strongly correlated system. We employ the short iterative Lanczos method as the time-integrator, which provides a unitary, norm-conserving, and stable long-time propagation scheme. We used the TD-ASCI method to evaluate the time-domain correlation functions of molecular systems. The accuracy of the correlation function was assessed by Fourier transforming into the frequency domain to compute the dipole-allowed absorption spectra. The Fourier transform (FT) has been carried out with a short-time signal of the correlation function to reduce the computation time, using an efficient alternative FT scheme based on the ESPRIT signal processing algorithm. We have applied the TD-ASCI method to prototypical strongly correlated molecular systems and compared the absorption spectra to spectra evaluated using the equation of motion coupled cluster method with a truncation at the singles, doubles, and triples level.
Modeling the time-resolved Coulomb explosion imaging of halomethane photodissociation with <i>ab initio</i> potential energy curves
We present an effective theoretical model to simulate observables in time-resolved two-fragment Coulomb explosion experiments. The model employs the potential energy curves of the neutral molecule and the doubly charged cation along a predefined reaction coordinate to simulate the photodissociation process followed by Coulomb explosion. We compare our theoretical predictions with pump–probe experiments on iodomethane and bromoiodomethane. Our theory successfully predicts the two reaction channels in iodomethane photodissociation that lead to I(P3/22) and I*(P1/22) products, showing excellent agreement with experimental delay-dependent kinetic energy release signals at large pump–probe delays. The theoretical kinetic energy release at small delays depends significantly on the choice of ionic states. By accounting for internal rotation, the kinetic energies of individual fragments in bromoiodomethane align well with experimental results. Furthermore, our theory confirms that two-fragment Coulomb explosion imaging cannot resolve different spin channels in bromoiodomethane photodissociation.
How many distinct and reliable multireference diagnostics are there?
Economical multireference (MR) diagnostics are essential for high-throughput computational studies, enabling the rapid and accurate identification of molecules affected by nondynamic correlation within large molecular datasets. Although various MR diagnostics have been proposed, benchmarking studies that help identify the criteria for an effective diagnostic are still scarce. In this article, we examine a wide range of correlation measures to evaluate their potential as MR diagnostics. We identify a small set of valid size-intensive correlation measures based on maximum metrics, exhibiting similar predictive values. Among these, we highlight INDmax, which offers an easy interpretation: it captures the largest deviation of a natural orbital occupancy from the boundary values corresponding to a single-reference wave function. No energy-based correlation measure was found suitable for constructing MR diagnostics. Finally, we demonstrate how average correlation measures, although not suitable as MR diagnostics, can provide a more comprehensive view of electron correlation within the molecule.
Isotopic separation in mixed clusters of molecular hydrogen
We investigate mixed (50/50) clusters of parahydrogen and orthodeuterium at low temperatures, by means of quantum Monte Carlo simulations. Our results provide evidence of liquid-like behavior and partial isotopic separation in a cluster of 640 molecules, at temperature T = 10 K. As the temperature is lowered below ∼6 K, crystallization occurs, with no indication that the liquid phase is more resilient at low temperatures in a mixed cluster. Isotopic separation is therefore predicted to take place at low temperatures only through the slow process of molecular self-diffusion in a crystalline matrix.
Structure of molten ytterbium aluminum garnet
Rare earth aluminum garnets are important materials in optical, dielectric, and thermal barrier applications. To advance the understanding of their melt processing and glass forming ability, we report the atomic structure of molten Yb3Al5O12 over 1770–2630 K, which spans the equilibrium and supercooled liquid regimes. The melt density at Tm = 2283 K is 5.50 g cm−3, measured via silhouette imaging of electrostatically levitated drops over 1010–2420 K. Four separate structure measurements were made with aerodynamically levitated melts using x-ray and neutron diffraction with isotope substitution of Yb (172Yb, 174Yb, or natYb). Empirical potential structure refinement models were developed, which are in excellent agreement with the experiments. Coordination environments for Al–O are predominantly 4- and 5-coordinate, with a mean coordination of nAlO = 4.43(8), while Yb–O environments mostly range from 5- to 8-coordinate, with nYbO = 6.26(8). The cation–oxygen polyhedra are connected primarily by corner-sharing, with edge-sharing constituting up to ∼1/3 of the connectivity among polyhedra with Yb or higher-coordinated Al–O. Structurally, the –Al–O– network in molten Yb3Al5O12 appears conducive to glass formation: nOAl = 1.85(3), there are 1.86 AlOx–AlOx connections per Al atom (e.g., a mixture of Q3 and Q4 units), and the modal ring size is six cations. These characterize a network that is somewhat less constrained compared to SiO2 glass, yet Yb3Al5O12 cannot be quenched into crystal-free glass. Aluminum garnet compositions with larger rare earth cations do form glass, so these characterizations help reveal the structural characteristics corresponding to the limit of glass forming ability in rare earth aluminates.
Influence of defect-state on the carrier dynamics in MAPbI3 polycrystalline films
In this paper, a transient absorption microscope with submicron resolution is used to detect the internal and grain boundary regions of the prepared polycrystalline thin film grains, and the obtained transient absorption spectra are subjected to singular value decomposition and global fitting. The contributions of hot carriers, cooled carriers, and defect-trapped carriers to the transient absorption signals and the dynamic evolution of the carriers among themselves are elucidated. By comparing the carrier dynamics taking place at the boundary and internal regions, we find that the benign shallow defect state in the grain boundary region has a positive effect on accelerating the cooling of hot carriers, while the deep energy level defects induce excited state absorption signals. This study provides a basis for further understanding the effect of grain boundary defects on the performance of polycrystal perovskite devices.