Search

Electron attachment to pyridine results in electronic resonances, metastable states that can decay through electronic or nuclear degrees of freedom. This study uses orbital stabilization techniques combined with bound electronic structure methods, based on equation of motion coupled cluster or multi-reference methods, to calculate positions and widths of electronic resonances in pyridine that exist below 10 eV. We report four 2B1 and four 2A2 resonances, including one 2B1 not previously reported experimentally and two 2A2 resonances not reported at all in the literature. The two lower energy resonances are one-particle shape resonances, while the remaining are mixed or primarily core-excited resonances. Multi-reference perturbation theory provides the best description of these resonances, especially when their character is mixed. We describe the character of these resonances qualitatively and calculate Dyson orbitals, which provide information about their decay channels. [ABSTRACT FROM AUTHOR]

Under isothermal conditions, phase transitions occur through a nucleation event when conditions are sufficiently close to coexistence. The formation of a nucleus of the new phase requires the system to overcome a free energy barrier of formation, whose height rapidly rises as supersaturation decreases. This phenomenon occurs both in the bulk and under confinement and leads to a very slow kinetics for the transition, ultimately resulting in hysteresis, where the system can remain in a metastable state for a long time. This has broad implications, for instance, when using simulations to predict phase diagrams or screen porous materials for gas storage applications. Here, we leverage simulations in an adiabatic statistical ensemble, known as adiabatic grand-isochoric ensemble (μ, V, L) ensemble, to reach equilibrium states with a greater efficiency than its isothermal counterpart, i.e., simulations in the grand-canonical ensemble. For the bulk, we show that at low supersaturation, isothermal simulations converge slowly, while adiabatic simulations exhibit a fast convergence over a wide range of supersaturation. We then focus on adsorption and desorption processes in nanoporous materials, assess the reliability of (μ, V, L) simulations on the adsorption of argon in IRMOF-1, and demonstrate the efficiency of adiabatic simulations to predict efficiently the equilibrium loading during the adsorption and desorption of argon in MCM-41, a system that exhibits significant hysteresis. We provide quantitative measures of the increased rate of convergence when using adiabatic simulations. Adiabatic simulations explore a wide temperature range, leading to a more efficient exploration of the configuration space. [ABSTRACT FROM AUTHOR]

The committor constitutes the primary quantity of interest within chemical kinetics as it is understood to encode the ideal reaction coordinate for a rare reactive event. We show the generative utility of the committor in that it can be used explicitly to produce a reactive trajectory ensemble that exhibits numerically exact statistics as that of the original transition path ensemble. This is done by relating a time-dependent analog of the committor that solves a generalized bridge problem to the splitting probability that solves a boundary value problem under a bistable assumption. By invoking stochastic optimal control and spectral theory, we derive a general form for the optimal controller of a bridge process that connects two metastable states expressed in terms of the splitting probability. This formalism offers an alternative perspective into the role of the committor and its gradients in that they encode force fields that guarantee reactivity, generating trajectories that are statistically identical to the way that a system would react autonomously. [ABSTRACT FROM AUTHOR]

Photoexcitation is a powerful way to induce phase transition of strongly correlated materials and dynamically control terahertz (THz) devices integrated with photoinduced phase transition (PIPT) materials. To clarify controversies over the physical mechanism between electronic insulator-metal transition (IMT) and structural phase transition (SPT) of photoexcited vanadium dioxide (VO 2), the underlying atomic and electronic state changes during photoinduced monoclinic-to-rutile phase transition are illustrated, and the separation with different thresholds between the quasi-instantaneous IMT and the ultrafast SPT is discovered. Below the SPT threshold, there exist metastable states exhibiting the metal-like monoclinic phases, i.e., the strongest metallicity and weak monoclinic phases, when the bond lengths of the V–V pairs are closest. By analyzing the electronic transport properties of these metal-like monoclinic phases, the THz response of the whole phase transition process can be characterized for first time through the quantum-electromagnetic dispersion modeling method. The THz properties of the practical VO 2 film are simulated and the great alignments between the measurements and the simulations verify the proposed analysis method, which provides a powerful exploration path and insights for the theoretical analysis and design verification of PIPT materials and their optoelectronic THz devices. [ABSTRACT FROM AUTHOR]

Photoexcitation is a powerful way to induce phase transition of strongly correlated materials and dynamically control terahertz (THz) devices integrated with photoinduced phase transition (PIPT) materials. To clarify controversies over the physical mechanism between electronic insulator-metal transition (IMT) and structural phase transition (SPT) of photoexcited vanadium dioxide (VO 2), the underlying atomic and electronic state changes during photoinduced monoclinic-to-rutile phase transition are illustrated, and the separation with different thresholds between the quasi-instantaneous IMT and the ultrafast SPT is discovered. Below the SPT threshold, there exist metastable states exhibiting the metal-like monoclinic phases, i.e., the strongest metallicity and weak monoclinic phases, when the bond lengths of the V–V pairs are closest. By analyzing the electronic transport properties of these metal-like monoclinic phases, the THz response of the whole phase transition process can be characterized for first time through the quantum-electromagnetic dispersion modeling method. The THz properties of the practical VO 2 film are simulated and the great alignments between the measurements and the simulations verify the proposed analysis method, which provides a powerful exploration path and insights for the theoretical analysis and design verification of PIPT materials and their optoelectronic THz devices. [ABSTRACT FROM AUTHOR]

The projected complex absorbing potential (CAP) technique is one of the methods that allow one to extend the bound state methods for computing resonances' energies and widths. Here, we explore the accuracy of the potential energy curves generated with different electronic structure theory methods in combination with the projected CAP technique by considering resonant vibrational excitation (RVE) of N2 by electron impact as a model process. We report RVE cross sections computed using the boomerang model with potential energy curves obtained with CAP-based extended multistate complete active space perturbation theory (XMS-CASPT2) and equation of motion coupled-cluster method for electron attachment with single and double substitution (EOM-EA-CCSD) methods. We also compare potential energy curves computed with several electronic structure methods, including XMS-CASPT2, EOM-EA-CCSD, multireference configuration interaction with singles (MR-CIS) and singles and doubles (MR-CISD). A good agreement is observed between the experiment and simulated RVE cross sections obtained with the potential energy curves generated with XMS-CASPT2 and EOM-EA-CCSD methods, thus highlighting the potential of the projected CAP technique combined with accurate electronic structure methods for dynamical simulations of the processes that proceed through metastable electronic states. [ABSTRACT FROM AUTHOR]

The projected complex absorbing potential (CAP) technique is one of the methods that allow one to extend the bound state methods for computing resonances' energies and widths. Here, we explore the accuracy of the potential energy curves generated with different electronic structure theory methods in combination with the projected CAP technique by considering resonant vibrational excitation (RVE) of N2 by electron impact as a model process. We report RVE cross sections computed using the boomerang model with potential energy curves obtained with CAP-based extended multistate complete active space perturbation theory (XMS-CASPT2) and equation of motion coupled-cluster method for electron attachment with single and double substitution (EOM-EA-CCSD) methods. We also compare potential energy curves computed with several electronic structure methods, including XMS-CASPT2, EOM-EA-CCSD, multireference configuration interaction with singles (MR-CIS) and singles and doubles (MR-CISD). A good agreement is observed between the experiment and simulated RVE cross sections obtained with the potential energy curves generated with XMS-CASPT2 and EOM-EA-CCSD methods, thus highlighting the potential of the projected CAP technique combined with accurate electronic structure methods for dynamical simulations of the processes that proceed through metastable electronic states. [ABSTRACT FROM AUTHOR]

Here, we investigate the hypothesis that despite the existence of at least two high-density amorphous ices, only one high-density liquid state exists in water. We prepared a very-high-density amorphous ice (VHDA) sample and rapidly increased its temperature to around 205 ± 10 K using laser-induced isochoric heating. This temperature falls within the so-called "no-man's land" well above the glass-liquid transition, wherein the IR laser pulse creates a metastable liquid state. Subsequently, this high-density liquid (HDL) state of water decompresses over time, and we examined the time-dependent structural changes using short x-ray pulses from a free electron laser. We observed a liquid–liquid transition to low-density liquid water (LDL) over time scales ranging from 20 ns to 3 μs, consistent with previous experimental results using expanded high-density amorphous ice (eHDA) as the initial state. In addition, the resulting LDL derived both from VHDA and eHDA displays similar density and degree of inhomogeneity. Our observation supports the idea that regardless of the initial annealing states of the high-density amorphous ices, the same HDL and final LDL states are reached at temperatures around 205 K. [ABSTRACT FROM AUTHOR]

Protein conformational changes play crucial roles in their biological functions. In recent years, the Markov State Model (MSM) constructed from extensive Molecular Dynamics (MD) simulations has emerged as a powerful tool for modeling complex protein conformational changes. In MSMs, dynamics are modeled as a sequence of Markovian transitions among metastable conformational states at discrete time intervals (called lag time). A major challenge for MSMs is that the lag time must be long enough to allow transitions among states to become memoryless (or Markovian). However, this lag time is constrained by the length of individual MD simulations available to track these transitions. To address this challenge, we have recently developed Generalized Master Equation (GME)-based approaches, encoding non-Markovian dynamics using a time-dependent memory kernel. In this Tutorial, we introduce the theory behind two recently developed GME-based non-Markovian dynamic models: the quasi-Markov State Model (qMSM) and the Integrative Generalized Master Equation (IGME). We subsequently outline the procedures for constructing these models and provide a step-by-step tutorial on applying qMSM and IGME to study two peptide systems: alanine dipeptide and villin headpiece. This Tutorial is available at https://github.com/xuhuihuang/GME%5ftutorials. The protocols detailed in this Tutorial aim to be accessible for non-experts interested in studying the biomolecular dynamics using these non-Markovian dynamic models. [ABSTRACT FROM AUTHOR]

Continued increases in computational power now make it possible to evaluate the free-energy landscape associated with the first-order liquid–liquid transition in realistic models of water for which an accurate estimate of the liquid–liquid critical point exists, and to explore its change with pressure near the coexistence line. We report the results of 50 μs-long NPT umbrella sampling simulations for two realistic models for water, TIP4P/2005 and TIP4P/ice, 3–9 K below their critical temperatures. The free energy profile at different pressures clearly shows the presence of two well-defined free energy basins and makes it possible to identify the liquid–liquid spinodal points, the limits of stability that define the (temperature dependent) pressure range within which two distinct free energy basins exist. The results show that for temperatures less than 10 K below the critical temperature, metastable states are possible across a very limited pressure interval, information that is relevant to the interpretation of experiments probing the metastable phase behavior of deeply supercooled water in the so-called no-man's land. [ABSTRACT FROM AUTHOR]

The long-time behavior of many complex molecular systems can often be described by Markovian dynamics in a slow subspace spanned by a few reaction coordinates referred to as collective variables (CVs). However, determining CVs poses a fundamental challenge in chemical physics. Depending on intuition or trial and error to construct CVs can lead to non-Markovian dynamics with long memory effects, hindering analysis. To address this problem, we continue to develop a recently introduced deep-learning technique called spectral map [J. Rydzewski, J. Phys. Chem. Lett. 14, 5216–5220 (2023)]. Spectral map learns slow CVs by maximizing a spectral gap of a Markov transition matrix describing anisotropic diffusion. Here, to represent heterogeneous and multiscale free-energy landscapes with spectral map, we implement an adaptive algorithm to estimate transition probabilities. Through a Markov state model analysis, we validate that spectral map learns slow CVs related to the dominant relaxation timescales and discerns between long-lived metastable states. [ABSTRACT FROM AUTHOR]

The time-dependent relaxation of a dynamical system may exhibit a power-law behavior that is superimposed by log-periodic oscillations. D. Sornette [Phys. Rep. 297, 239 (1998)] showed that this behavior can be explained by a discrete scale invariance of the system, which is associated with discrete and equidistant timescales on a logarithmic scale. Examples include such diverse fields as financial crashes, random diffusion, and quantum topological materials. Recent time-resolved experiments and molecular dynamics simulations suggest that discrete scale invariance may also apply to hierarchical dynamics in proteins, where several fast local conformational changes are a prerequisite for a slow global transition to occur. Employing entropy-based timescale analysis and Markov state modeling to a simple one-dimensional hierarchical model and biomolecular simulation data, it is found that hierarchical systems quite generally give rise to logarithmically spaced discrete timescales. By introducing a one-dimensional reaction coordinate that collectively accounts for the hierarchically coupled degrees of freedom, the free energy landscape exhibits a characteristic staircase shape with two metastable end states, which causes the log-periodic time evolution of the system. The period of the log-oscillations reflects the effective roughness of the energy landscape and can, in simple cases, be interpreted in terms of the barriers of the staircase landscape. [ABSTRACT FROM AUTHOR]

Computational study of electronic resonances is still a very challenging topic, with the phenomenon of dissociative electron attachment (DEA) being one of the multiple features worth investigating. Recently, we extended the charge stabilization method from energies to properties of conceptual density functional theory and applied this to metastable anionic states of ethene and chlorinated ethene derivatives to study the DEA mechanism present in these compounds. We now present an extension to spatial functions, namely, the electronic Fukui function and the electron localization function. The results of our analysis show that extrapolated spatial functions are relevant and useful for more precise localization of the unbound electron. Furthermore, we report for the first time the combination of the electron localization function with Berlin's binding function for these challenging electronic states. This promising methodology allows for accurate predictions of when and where DEA will happen in the molecules studied and provides more insight into the process. [ABSTRACT FROM AUTHOR]

Simulations of condensed matter systems often focus on the dynamics of a few distinguished components but require integrating the full system. A prime example is a molecular dynamics simulation of a (macro)molecule in a solution, where the molecule(s) and the solvent dynamics need to be integrated, rendering the simulations computationally costly and often unfeasible for physically/biologically relevant time scales. Standard coarse graining approaches can reproduce equilibrium distributions and structural features but do not properly include the dynamics. In this work, we develop a general data-driven coarse-graining methodology inspired by the Mori–Zwanzig formalism, which shows that macroscopic systems with a large number of degrees of freedom can be described by a few relevant variables and additional noise and memory terms. Our coarse-graining method consists of numerical integrators for the distinguished components, where the noise and interaction terms with other system components are substituted by a random variable sampled from a data-driven model. The model is parameterized using data from multiple short-time full-system simulations, and then, it is used to run long-time simulations. Applying our methodology to three systems—a distinguished particle under a harmonic and a bistable potential and a dimer with two metastable configurations—the resulting coarse-grained models are capable of reproducing not only the equilibrium distributions but also the dynamic behavior due to temporal correlations and memory effects. Remarkably, our method even reproduces the transition dynamics between metastable states, which is challenging to capture correctly. Our approach is not constrained to specific dynamics and can be extended to systems beyond Langevin dynamics, and, in principle, even to non-equilibrium dynamics. [ABSTRACT FROM AUTHOR]

In polymers, the equilibrium state is achieved when the chains have access to the maximum number of conformational states, which allows them to explore a larger conformational space, leading to an increase in the entropy of the system. Preparation of thin polymer films using the spin-coating technique results in polymer chains being locked in a nonequilibrium state with lower entropy due to possible stretching of chains during the process. Allowing enough time for recovery results in the relaxation of the spin-coating-induced molecular recoiling stress. Annealing such a film generates entropy due to its inherent irreversibility. We employed the dewetting technique to determine the molecular recoiling stress relaxation time in poly-(tertbutyl styrene) thin films. Furthermore, we qualitatively differentiated the metastable states achieved by the polymer film using entropy generation in a relaxing polymer film as an effect of thermal entropy and associated it with the conformational entropy of polymer chains utilizing the molecular recoiling stress relaxation time. This enabled us to explain molecular recoiling stress relaxation using a rather simplistic approach involving segmental level molecular rearrangements in polymer chains by attaining transient metastable states through an entropically activated process driving toward equilibrium. [ABSTRACT FROM AUTHOR]

We have investigated the impact of microsolvation on shape-type resonance states of nucleobases, taking cytosine as a case study. To characterize the resonance position and decay width of the metastable states, we employed the newly developed DLPNO-based EA-EOM-CCSD method in conjunction with the resonance via Padé (RVP) method. Our calculations show that the presence of water molecules causes a redshift in the resonance position and an increase in the lifetime for the three lowest-lying resonance states of cytosine. Furthermore, there are some indications that the lowest resonance state in isolated cytosine may get converted to a bound state in the presence of an aqueous environment. The obtained results are extremely sensitive to the basis set used for the calculations. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) is the method of choice for understanding the structure, function, and interactions of molecules. However, MD simulations are limited by the strong metastability of many molecules, which traps them in a single conformation basin for an extended amount of time. Enhanced sampling techniques, such as metadynamics and replica exchange, have been developed to overcome this limitation and accelerate the exploration of complex free energy landscapes. In this paper, we propose Vendi Sampling, a replica-based algorithm for increasing the efficiency and efficacy of the exploration of molecular conformation spaces. In Vendi sampling, replicas are simulated in parallel and coupled via a global statistical measure, the Vendi Score, to enhance diversity. Vendi sampling allows for the recovery of unbiased sampling statistics and dramatically improves sampling efficiency. We demonstrate the effectiveness of Vendi sampling in improving molecular dynamics simulations by showing significant improvements in coverage and mixing between metastable states and convergence of free energy estimates for four common benchmarks, including Alanine Dipeptide and Chignolin. [ABSTRACT FROM AUTHOR]

Cardiac muscle contraction is initiated by an elementary Ca signal (called Ca spark) which is achieved by collective action of Ca release channels in a cluster. The mechanism of this synchronization remains uncertain. We approached Ca spark activation as an emergent phenomenon of an interactive system of release channels. We constructed a weakly lumped Markov chain that applies an Ising model formalism to such release channel clusters and probable open channel configurations and demonstrated that spark activation is described as a system transition from a metastable to an absorbing state, analogous to the pressure required to overcome surface tension in bubble formation. This yielded quantitative estimates of the spark generation probability as a function of various system parameters. We performed numerical simulations to find spark probabilities as a function of sarcoplasmic reticulum Ca concentration, obtaining similar values for spark activation threshold as our analytic model, as well as those reported in experimental studies. Our parametric sensitivity analyses also showed that the spark activation threshold decreased as Ca sensitivity of RyR activation and RyR cluster size increased. [ABSTRACT FROM AUTHOR]

Interpreting high-dimensional data from molecular dynamics simulations is a persistent challenge. In this paper, we show that for a small peptide, deca-alanine, metastable states can be identified through a neural net based on structural information alone. While processing molecular dynamics data, dimensionality reduction is a necessary step that projects high-dimensional data onto a low-dimensional representation that, ideally, captures the conformational changes in the underlying data. Conventional methods make use of the temporal information contained in trajectories generated through integrating the equations of motion, which forgoes more efficient sampling schemes. We demonstrate that EncoderMap, an autoencoder architecture with an additional distance metric, can find a suitable low-dimensional representation to identify long-lived molecular conformations using exclusively structural information. For deca-alanine, which exhibits several helix-forming pathways, we show that this approach allows us to combine simulations with different biasing forces and yields representations comparable in quality to other established methods. Our results contribute to computational strategies for the rapid automatic exploration of the configuration space of peptides and proteins. [ABSTRACT FROM AUTHOR]

In the present work, we study the effect of quenching and annealing on the ferroelectric and piezoelectric properties at room temperature and elevated temperatures of a new ternary BiFeO3-PbTiO3-Li0.5Bi0.5TiO3 bulk piezo ceramic. While sacrificing part of the maximally obtainable piezoelectric constant value, using an optimal heat treatment, a quasi-stable value for the piezoelectric constant of 65 pC/N was obtained irrespective of the annealing temperature. All experimental results point to the direction of unusual defect behavior in this novel ternary system leading to a well-defined metastable state. The quenching and annealing process are completely reversible and can be used in combination with additional chemical modifications to tailor the properties of this new high-temperature piezoelectric ceramic to the intended use conditions. [ABSTRACT FROM AUTHOR]

Salicylideneaniline (SA) is an archetypal system for excited-state intramolecular proton transfer (ESIPT) in non-planar systems. Multiple channels for relaxation involving both the keto and enol forms have been proposed after excitation to S1 with near-UV light. Here, we present transient absorption measurements of hot gas-phase SA, jet-cooled SA, and SA in Ar clusters using cavity-enhanced transient absorption spectroscopy (CE-TAS). Assignment of the spectra is aided by simulated TAS spectra, computed by applying time-dependent complete active space configuration interaction (TD-CASCI) to structures drawn from nonadiabatic molecular dynamics simulations. We find prompt ESIPT in all conditions followed by the rapid generation of the trans keto metastable photochrome state and fluorescent keto state in parallel. Increasing the internal energy increases the photochrome yield and decreases the fluorescent yield and fluorescent state lifetime observed in TAS. In Ar clusters, internal conversion of SA is severely hindered, but the photochrome yield is unchanged. Taken together, these results are consistent with the photochrome being produced via the vibrationally excited keto population after ESIPT. [ABSTRACT FROM AUTHOR]

Cyclodextrin‐based polyrotaxanes (CD‐PRs) are gaining attention for their dynamic sliding rings along the polymer axis, enabling various applications in molecular shuttles, drug delivery, and durable polymers with slidable cross‐links. However, the conventional synthesis of CD‐PRs with tunable threading ratios is typically laborious, time‐consuming, and complicated, which limits their scalability and cost‐effectiveness. Herein, we highlight the great potential of planetary centrifugal mixing, a process that significantly accelerates and simplifies the initial synthesis of polypseudorotaxanes (PPRs), followed by a thiol‐ene click reaction as an efficient end‐capping reaction for the synthesis of PRs. Notably, PRs synthesized with glutathione (GSH) as the end‐capping reagent are in a metastable state, where GSH act as a molecular bumper that significantly prevent de‐threading of α‐CD rings at room temperature. Moreover, the rate of ring de‐threading can be precisely controlled by heating, enabling the preparation of metastable PRs with tunable threading ratios over a wide range. The developed strategy is of great significance to the efficient synthesis of CD‐PRs, thus marking a significant step towards their practical application in advanced functional materials and devices. [ABSTRACT FROM AUTHOR]

This study utilizes molecular dynamics simulation to investigate the complex dynamics of entangled semi-flexible polymer melts. The investigation reveals a significant stress overshoot phenomenon in the systems, demonstrating the intricate interplay between shear rates, chain orientation, and chain stretching dynamics. Additionally, the identification of metastable states, characterized by a dual-plateau phenomenon in the shear stress-strain curve at specific Rouse-Weissenberg number WiR, showcases the system's responsiveness to external perturbations and its transition to stable shear banding states. Moreover, the analysis of flow field deviations uncovers a progression of shear bands with increasing WiR, displaying distinct behaviors in the system's dynamics under different shear rates and chain lengths. These findings challenge established theoretical frameworks and advocate for refined modelling approaches in polymer rheology research. [ABSTRACT FROM AUTHOR]

In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behavior. The resulting polarons play a central role in many materials properties including electrical transport, interaction with light, surface reactivity, and magnetoresistance, and polarons are typically investigated indirectly through these macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in Fe2O3 at the single quasiparticle limit. A combination of Kelvin probe force microscopy (KPFM) and kinetic Monte Carlo (KMC) simulations shows that the mobility of electron polarons can be markedly increased by Ti doping. Density functional theory (DFT) calculations indicate that a transition from polaronic to metastable free-carrier states can play a key role in migration of electron polarons. In contrast, hole polarons are significantly less mobile, and their hopping is hampered further by trapping centers. [ABSTRACT FROM AUTHOR]

[Display omitted] Phase behavior of nanoconfined fluids adsorbed in metal–organic frameworks is of paramount importance for the design of advanced materials for energy and gas storage, separations, electrochemical devices, sensors, and drug delivery, as well as for the pore structure characterization. Phase transformations in adsorbed fluids often involve long-lasting metastable states and hysteresis that has been well-documented in gas adsorption–desorption and nonwetting fluid intrusion-extrusion experiments. However, theoretical prediction of the observed nanophase behavior remains a challenging problem. The mesoscopic canonical, or mesocanonical, ensemble (MCE) is devised to study the nanophase behavior under conditions of controlled fluctuations to stabilize metastable and labile states. Here, we implement and apply the MCE Monte Carlo (MCEMC) simulation scheme to predict the origins of reversible and hysteric adsorption phase transitions in a series of practical MOF materials, including IRMOF-1, ZIF-412, UiO-66, Cu-BTC, IRMOF-74-V, VII, and IX. The MCEMC method, called the gauge cell method, allows to produce Van der Waals type isotherms with distinctive swings around the phase transition regions. The constructed isotherms determine the positions of phase equilibrium and spinodals, as well as the nucleation barriers separating metastable states. We demonstrate the unique capabilities of the MCEMC method in quantitative predictions of experimental observations compared with the conventional grand canonical and canonical ensemble simulations. The MCEMC method is implemented in the open-source RASPA and LAMMPS software packages and recommended for studies of adsorption behavior and pore structure characterization of MOFs and other nanoporous materials. [ABSTRACT FROM AUTHOR]

Defect-related spin-to-photon interfaces in silicon promise the realization of quantum repeaters by combining advanced semiconductor and photonics technologies. Recently, controlled creation/erasure of simple carbon interstitial defects have been successfully realised in silicon. This defect has a stable structure near room temperature and coherently emits in the wave-length where the signal loss is minimal in optical fibres used in communication technologies. Our in-depth theoretical characterization confirms the assignment of the observed emission to the neutral charge state of this defect, as arising due to the recombination of a bound exciton. We also identified a metastable triplet state that could be applied as a quantum memory. Based on the analysis of the electronic structure of the defect and its similarities to a known optically detected magnetic resonance centre in silicon, we propose that a carbon interstitial can act as a quantum bit and may realize a spin-to-photon interface in complementary metal-oxide semiconductor-compatible platforms. This work presents a theoretical investigation of the single carbon interstitial (Ci) defect in silicon as a potential candidate for spin-photon interfaces. Computed charge transition levels and optical properties show good agreement with the experimental results and allow assigning the experimentally observed telecom zero-phonon emission (1448 nm) to the neutral Ci defect. [ABSTRACT FROM AUTHOR]

Cuprous oxide (Cu2O)‐based catalysts present a promising activity for the electrochemical nitrate (NO3−) reduction to ammonia (eNO3RA), but the electrochemical instability of Cu+ species may lead to an unsatisfactory durability, hindering the exploration of the structure‐performance relationship. Herein, we propose an efficient strategy to stabilize Cu+ through the incorporation of Cr4+ into the Cu2O matrix to construct a Cr4+−O−Cu+ network structure. In situ and quasi‐in situ characterizations reveal that the Cu+ species are well maintained via the strong Cr4+−O−Cu+ interaction that inhibits the leaching of lattice oxygen. Importantly, in situ generated Cr3+−O−Cu+ from Cr4+−O−Cu+ is identified as a dual‐active site for eNO3RA, wherein the Cu+ sites are responsible for the activation of N‐containing intermediates, while the assisting Cr3+ centers serve as the electron‐proton mediators for rapid water dissociation. Theoretical investigations further demonstrated that the metastable state Cr3+−O−Cu+ favors the conversion from the endoergic hydrogenation of the key *ON intermediate to an exoergic reaction in an ONH pathway, and facilitates the subsequent NH3 desorption with a low energy barrier. The superior eNO3RA with a maximum 91.6 % Faradaic efficiency could also be coupled with anodic sulfion oxidation to achieve concurrent NH3 production and sulfur recovery with reduced energy input. [ABSTRACT FROM AUTHOR]

The recent discovery of nickelate superconductivity represents an important step toward understanding the four‐decade mastery of unconventional high‐temperature superconductivity. However, the synthesis of the infinite‐layer nickelate superconductors shows great challenges. Particularly, surface capping layers are usually unitized to facilitate the sample synthesis. This leads to an important question whether nickelate superconductors with d9 configuration and ultralow valence of Ni1+ are in metastable state and whether nickelate superconductivity can be robust? In this work, a series of redox cycling experiments are performed across the phase transition between perovskite Nd0.8Sr0.2NiO3 and infinite‐layer Nd0.8Sr0.2NiO2. The infinite‐layer Nd0.8Sr0.2NiO2 is quite robust in the redox environment and can survive the cycling experiments with unchanged crystallographic quality. However, as the cycling number goes on, the perovskite Nd0.8Sr0.2NiO3 shows structural degradation, suggesting stability of nickelate superconductivity is not restricted by the ultralow valence of Ni1+, but by the quality of its perovskite precursor. The observed robustness of infinite‐layer Nd0.8Sr0.2NiO2 up to ten redox cycles further indicates that if an ideal high‐quality perovskite precursor can be obtained, infinite‐layer nickelate superconductivity can be very stable and sustainable under environmental conditions. This work provides important implications for potential device applications for nickelate superconductors. [ABSTRACT FROM AUTHOR]

Continuum shape‐morphing structures with the capability to encode memory and execute logic operations have garnered significant interest for the development of mechanical systems with embodied intelligence and soft robots. Achieving the integration of memory and computing within a mechanical system necessitates building blocks that possess a range of tunable, metastable states. Prior efforts have been dedicated to constructing mechanical memory and logic through the exploitation of snap‐through instabilities in multistable structures. Typically, the creation of each logic gate demands a distinct structural design. Here, presents an unconventional design strategy that leverages a single kirigami architecture to perform and switch between multiple fundamental logic operations. By utilizing the kirigami architecture as the fundamental element, mechanical signal transmission is demonstrated and half‐adder computations are performed. It is envisioned that this design strategy can be applied to a wide range of materials and structures, and reduce the complexity of developing materials systems with embodied intelligence. [ABSTRACT FROM AUTHOR]

CO is one of the important molecules in dense molecular clouds, and its dissociation induced by cosmic ray heavy ions is a fundamental process for molecular breaking up and rearrangement in astronomical networks. Extensive laboratory simulations are required to understand molecular evolution in astrophysical contexts. Here, we investigate the CO dissociation induced by 1 keV/u Ar 2 + using cold target recoil ion momentum spectroscopy. Kinetic energy release for double electron capture Ar 2 + + CO → Ar 0 + C + + O + and transfer ionization Ar 2 + + CO → Ar + + C + + O + + e − was obtained. The dissociation mechanisms are attributed to different KER distributions. The autoionization process is identified below the CO 2 + double ionization threshold. [ABSTRACT FROM AUTHOR]

Metastable multi‐element nanoalloys hold extensive potential for next‐generation batteries due to their distinct structures. However, it is difficult to obtain metastable nanoalloys through conventional equilibrium annealing. Herein, the rapid nanomanufacturing of metastable multi‐metallic nanoalloys is reported with single‐phase structure, ultrafine size distribution, and high‐density dispersion, realized by a novel nonequilibrium thermal shock (NTS) method. The NTS method, which features ultrafast heating/cooling rates and ultrashort treatment duration, can lead to the uniform mixing of different elements and the capture of the metastable state of multi‐element nanoalloys while preventing interparticle sintering/coarsening and phase separation. As a proof‐of‐concept demonstration, a metastable BiSnSb nanoalloy (M‐BiSnSb), prepared by the NTS method, exhibits rich lattice distortions and superior performance for potassium ion batteries (KIBs) compared with the stable BiSnSb (S‐BiSnSb) anode prepared by a typical equilibrium method. Additionally, in situ high‐temperature synchrotron X‐ray diffraction (SXRD) demonstrates the formation mechanism of M‐BiSnSb. Furthermore, in situ laboratory X‐ray diffraction (XRD) and molecular dynamics (MD) simulation systematically prove the alloying reaction mechanism and the structural advantages of the metastable nanoalloys in diffusion‐accelerating effect, respectively. This nonequilibrium nanomanufacturing strategy is expected to enable the rational and controllable synthesis of metastable nanomaterials for extensive electrochemical energy applications. [ABSTRACT FROM AUTHOR]

The condensation of amino acids into peptides plays a crucial role in protein synthesis and is thus essential for understanding the origins of life. However, the spontaneous formation of peptides from amino acids in bulk aqueous media is energetically unfavorable, posing a challenge for elucidating plausible abiotic mechanisms. In this study, we investigate the formation of amide bonds between amino acids within highly supersaturated aerosol droplets containing dicyandiamide (DCD), a cyanide derivative potentially present on primordial Earth. Metastable states, i.e. supersaturation, within individual micron‐sized droplets are studied using both an optical trap and a linear quadrupole electrodynamic balance. When irradiated with intense visible light, amide bond formation is observed to occur and can be monitored using vibrational bands in Raman spectra. The reaction rate is found to be strongly influenced by droplet size and kinetic modelling suggests that it is driven by the photochemical product of a DCD self‐reaction. Our results highlight the potential of atmospheric aerosol particles as reaction environments for peptide synthesis and have potential implications for the prebiotic chemistry of early Earth. [ABSTRACT FROM AUTHOR]

This work investigates the role of stable (sing-phased) and unstable (bi-phased) lattice structures in controlling the magnetic spin order and electronic properties in Co-rich ferrites of compositions Co1.25Fe1.75O4 and Co2.25Fe0.75O4. The material was synthesized via the chemical reaction of metal (Co and Fe) nitrates in an alkaline medium and post-heat treatment. The XRD patterns of Co1.25Fe1.75O4 showed a single-phased structure upon heat treatment in the temperature range of 200–900 °C, whereas Co2.25Fe0.75O4 showed a single-phased structure at 900 °C and bi-phased structure at a low heating temperature range of 200–800 °C. The thermally induced irreversibility (non-equilibrium) effect was observed in the lattice structure, magnetic spin order and electrical conductivity. The lattice structure at the (local) microscopic scale showed a more or less metastable state and coexistence of mixed-charge states of Co and Fe ions, irrespective of the single or bi-phased structure. The magnetic and electronic responses are found to be sensitive enough to detect local level non-equilibrium (metastable) states in non-equilibrium and equilibrium crystalline phases seen from XRD patterns. [ABSTRACT FROM AUTHOR]

Nature uses complex self‐assembly pathways to access distinct functional non‐equilibrium self‐assemblies. This remarkable ability to steer same set of biomolecules into different self‐assembly states is done by avoiding thermodynamic pit. In synthetic systems, on demand control over 'Pathway Complexity' to access self‐assemblies different from equilibrium structures remains challenging. Here we show versatile non‐equilibrium assemblies of the same monomer via alternate assembly pathways. The assemblies nucleate using non‐classical or classical nucleation routes into distinct metastable (transient hydrogels), kinetic (stable hydrogels) and thermodynamic structures [(poly)‐crystals and 2D sheets]. Initial chemical and thermal inputs force the monomers to follow different assembly pathways and form soft‐materials with distinct molecular arrangements than at equilibrium. In many cases, equilibrium structures act as thermodynamic sink which consume monomers from metastable structures giving transiently formed materials. This dynamics can be tuned chemically or thermally to slow down the dissolution of transient hydrogel, or skip the intermediate hydrogel altogether to reach final equilibrium assemblies. If required this metastable state can be kinetically trapped to give strong hydrogel stable over days. This method to control different self‐assembly states can find potential use in similar biomimetic systems to access new materials for various applications. [ABSTRACT FROM AUTHOR]

In binding free energy calculations, simulations must sample all relevant conformations of the system in order to obtain unbiased results. For instance, different ligands can bind to different metastable states of a protein, and if these protein conformational changes are not sampled in relative binding free energy calculations, the contribution of these states to binding is not accounted for and thus calculated binding free energies are inaccurate. In this work, we investigate the impact of different beta‐sectretase 1 (BACE1) protein conformations obtained from x‐ray crystallography on the binding of BACE1 inhibitors. We highlight how these conformational changes are not adequately sampled in typical molecular dynamics simulations. Furthermore, we show that insufficient sampling of relevant conformations induces substantial error in relative binding free energy calculations, as judged by a variation in calculated relative binding free energies up to 2 kcal/mol depending on the starting protein conformation. These results emphasize the importance of protein conformational sampling and pose this BACE1 system as a challenge case for further method development in the area of enhanced protein conformational sampling, either in combination with binding calculations or as an endpoint correction. [ABSTRACT FROM AUTHOR]

Oscillatory complex networks in the metastable regime have been used to study the emergence of integrated and segregated activity in the brain, which are hypothesised to be fundamental for cognition. Yet, the parameters and the underlying mechanisms necessary to achieve the metastable regime are hard to identify, often relying on maximising the correlation with empirical functional connectivity dynamics. Here, we propose and show that the brain's hierarchically modular mesoscale structure alone can give rise to robust metastable dynamics and (metastable) chimera states in the presence of phase frustration. We construct unweighted 3-layer hierarchical networks of identical Kuramoto-Sakaguchi oscillators, parameterized by the average degree of the network and a structural parameter determining the ratio of connections between and within blocks in the upper two layers. Together, these parameters affect the characteristic timescales of the system. Away from the critical synchronization point, we detect the emergence of metastable states in the lowest hierarchical layer coexisting with chimera and metastable states in the upper layers. Using the Laplacian renormalization group flow approach, we uncover two distinct pathways towards achieving the metastable regimes detected in these distinct layers. In the upper layers, we show how the symmetry-breaking states depend on the slow eigenmodes of the system. In the lowest layer instead, metastable dynamics can be achieved as the separation of timescales between layers reaches a critical threshold. Our results show an explicit relationship between metastability, chimera states, and the eigenmodes of the system, bridging the gap between harmonic based studies of empirical data and oscillatory models. [ABSTRACT FROM AUTHOR]

The Fermi–Pasta–Ulam–Tsingou (FPUT) paradox is the phenomenon whereby a one-dimensional chain of oscillators with nonlinear couplings shows long-lived nonergodic behavior prior to thermalization. The trajectory of the system in phase space, with a long-wavelength initial condition, closely follows that of the Toda model over short times, as both systems seem to relax quickly to a non-thermal, metastable state. Over longer times, resonances in the FPUT spectrum drive the system toward equilibrium, away from the Toda trajectory. Similar resonances are observed in q -breather spectra, suggesting that q -breathers are involved in the route toward thermalization. In this article, we first review previous important results related to the metastable state, solitons, and q -breathers. We then investigate orbit bifurcations of q -breathers and show that they occur due to resonances, where the q -breather frequencies become commensurate as m Ω 1 = Ω k. The resonances appear as peaks in the breather energy spectrum. Furthermore, they give rise to new "composite periodic orbits," which are nonlinear combinations of multiple q -breathers that exist following orbit bifurcations. We find that such resonances are absent in integrable systems, as a consequence of the (extensive number of) conservation laws associated with integrability. [ABSTRACT FROM AUTHOR]

After reviewing the peculiar thermodynamics and statistical mechanics of self-gravitating systems, we consider the case of a "binary star" consisting of two particles of size a in gravitational interaction in a box of radius R. The caloric curve of this system displays a region of negative specific heat in the microcanonical ensemble, which is replaced by a first-order phase transition in the canonical ensemble. The free energy viewed as a thermodynamic potential exhibits two local minima that correspond to two metastable states separated by an unstable maximum forming a barrier of potential. By introducing a Langevin equation to model the interaction of the particles with the thermal bath, we study the random transitions of the system between a "dilute" state, where the particles are well separated, and a "condensed" state, where the particles are bound together. We show that the evolution of the system is given by a Fokker–Planck equation in energy space and that the lifetime of a metastable state is given by the Kramers formula involving the barrier of free energy. This is a particular case of the theory developed in a previous paper (Chavanis, 2005) for N Brownian particles in gravitational interaction associated with the canonical ensemble. In the case of a binary star ( N = 2 ), all the quantities can be calculated exactly analytically. We compare these results with those obtained in the mean field limit N → + ∞ . [ABSTRACT FROM AUTHOR]

The influence of modernized three-electrode ion-plasma sputtering of a complex Fe–Si–B– (Cu, Nb)/(Ni, Mo) target on the structure and properties of sputtered films was studied. The formation of amorphous and nanocrystalline phases in Fe73Si15.8B7.2-(Cu, Nb)4 and Fe78.5Si6B14-(Ni, Mo)1.5 films with a coherent scattering region size of 1.6 nm and 12 nm, respectively, was established as a result of a modernized three-electrode ion - plasma sputtering. The thermal stability of metastable states of films as well as electrical and magnetic properties of freshly prepared and heat-treated films has been investigated. The conditions for obtaining films with low values of the temperature coefficient of electrical resistance (−0.9∙10−5 K−1) and coercive force (HC ∼11 A/m) have been determined. [ABSTRACT FROM AUTHOR]

The present work provides Potential Energy Curves (PECs) of both cyano radical CN and cyanide anion ${\rm CN}^{-}$ CN − up to the third asymptote of dissociation out of ab initio calculations. The [MRCI+Q] method is the level of theory used here and we have associated it with the Dunning basis set AV6Z (Augmented correlation-consistent polarised Valence sextet Zeta) for geometry optimisation of our systems. Electronic configurations of the states of the two species were explored and based on these configurations and the relative positions of the PECs of ${\rm CN}^{-}$ CN − against those of the neutral radical CN, stable and metastable states have been found and exhibited. The calculated electron affinity here that proves itself to be positive and the position of the ${\rm X}^{1}\Sigma ^+$ X 1 Σ + state against its corresponding neutral parent state (${\rm X}^{2}\Sigma ^+$ X 2 Σ + ) from which it derives led to confirm that this state is a long-lived and stable ground state of the cyanide anion ${\rm CN}^{-}$ CN − . Spectroscopic constants of both ground and low-lying excited states are calculated and exhibited in this work. [ABSTRACT FROM AUTHOR]

Copyright of Precious Metals / Guijinshu is the property of Precious Metals Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present work provides Potential Energy Curves (PECs) of both cyano radical CN and cyanide anion ${\rm CN}^{-}$ CN − up to the third asymptote of dissociation out of ab initio calculations. The [MRCI+Q] method is the level of theory used here and we have associated it with the Dunning basis set AV6Z (Augmented correlation-consistent polarised Valence sextet Zeta) for geometry optimisation of our systems. Electronic configurations of the states of the two species were explored and based on these configurations and the relative positions of the PECs of ${\rm CN}^{-}$ CN − against those of the neutral radical CN, stable and metastable states have been found and exhibited. The calculated electron affinity here that proves itself to be positive and the position of the ${\rm X}^{1}\Sigma ^+$ X 1 Σ + state against its corresponding neutral parent state (${\rm X}^{2}\Sigma ^+$ X 2 Σ + ) from which it derives led to confirm that this state is a long-lived and stable ground state of the cyanide anion ${\rm CN}^{-}$ CN − . Spectroscopic constants of both ground and low-lying excited states are calculated and exhibited in this work. [ABSTRACT FROM AUTHOR]

We extend a recently proposed kinetic theory of virus capsid assembly based on Model A kinetics and study the dynamics of the interconversion of virus capsids of different sizes triggered by a quench, that is, by sudden changes in the solution conditions. The work is inspired by in vitro experiments on functionalized coat proteins of the plant virus cowpea chlorotic mottle virus, which undergo a reversible transition between two different shell sizes (T = 1 and T = 3) upon changing the acidity and salinity of the solution. We find that the relaxation dynamics are governed by two time scales that, in almost all cases, can be identified as two distinct processes. Initially, the monomers and one of the two types of capsids respond to the quench. Subsequently, the monomer concentration remains essentially constant, and the conversion between the two capsid species completes. In the intermediate stages, a long-lived metastable steady state may present itself, where the thermodynamically less stable species predominate. We conclude that a Model A based relaxational model can reasonably describe the early and intermediate stages of the conversion experiments. However, it fails to provide a good representation of the time evolution of the state of assembly of the coat proteins in the very late stages of equilibration when one of the two species disappears from the solution. It appears that explicitly incorporating the nucleation barriers to assembly and disassembly is crucial for an accurate description of the experimental findings, at least under conditions where these barriers are sufficiently large. [ABSTRACT FROM AUTHOR]

Due to its numerous practical applications and intriguing phase transformation behavior, shape memory alloys (SMAs) have garnered significant research and development interests. In the past, most studies on the mechanical behavior of SMAs have been conducted under uniaxial stress loadings. Limited research on SMAs under shock loading has not provided conclusive results regarding their transformation behavior and transformation stress under such loading. Additionally, there is a lack of comprehensive understanding regarding the effects of different stress states on transformation behavior. The main objectives of this study are to address these issues. To achieve these objectives, a series of shock wave experiments were designed and conducted. Additionally, quasi-static and dynamic uniaxial stress experiments were carried out to establish a baseline for comparison. The results revealed that the transformation stress under dynamic uniaxial strain shock loading was approximately 1.92 GPa in contrast to 0.5 GPa (quasi-static) to 0.8 GPa (dynamic) observed in uniaxial stress loading. The transformation behavior exhibited noticeable rate sensitivity for both types of loading. There appeared to be a critical strain rate above which the austenite phase was driven to a metastable state. This estimated critical axial strain rate along the loading direction was approximately 2 × 103/s–4 × 103/s for uniaxial stress loading and approximately 2 × 106/s for uniaxial strain loading. The apparent high transformation stress for uniaxial strain loading can likely be attributed to a combination of high-pressure confinement and high strain rate. However, determining their relative contributions remains an open issue. [ABSTRACT FROM AUTHOR]

The Mpemba effect is a fingerprint of the anomalous relaxation phenomenon wherein an initially hotter system equilibrates faster than an initially colder system when both are quenched to the same low temperature. Experiments on a single colloidal particle trapped in a carefully shaped double well potential have demonstrated this effect recently [A. Kumar and J. Bechhoefer, Nature 584, 64 (2020)]. In a similar vein, here, we consider a piece-wise linear double well potential that allows us to demonstrate the Mpemba effect using an exact analysis based on the spectral decomposition of the corresponding Fokker–Planck equation. We elucidate the role of the metastable states in the energy landscape as well as the initial population statistics of the particles in showcasing the Mpemba effect. Crucially, our findings indicate that neither the metastability nor the asymmetry in the potential is a necessary or a sufficient condition for the Mpemba effect to be observed. [ABSTRACT FROM AUTHOR]

An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out. [ABSTRACT FROM AUTHOR]

Identifying a reduced set of collective variables is critical for understanding atomistic simulations and accelerating them through enhanced sampling techniques. Recently, several methods have been proposed to learn these variables directly from atomistic data. Depending on the type of data available, the learning process can be framed as dimensionality reduction, classification of metastable states, or identification of slow modes. Here, we present mlcolvar, a Python library that simplifies the construction of these variables and their use in the context of enhanced sampling through a contributed interface to the PLUMED software. The library is organized modularly to facilitate the extension and cross-contamination of these methodologies. In this spirit, we developed a general multi-task learning framework in which multiple objective functions and data from different simulations can be combined to improve the collective variables. The library's versatility is demonstrated through simple examples that are prototypical of realistic scenarios. [ABSTRACT FROM AUTHOR]

A non-equilibrium plasma is created in a micro-capillary quartz tube (800 µ m of internal diameter), by a DC-pulsed micro-dielectric barrier discharge (micro-DBD) and the propagation of an ionisation wave, in mixtures of He/H2O/VOC at atmospheric pressure where the studied volatile organic compounds (VOCs) are representative of molecules belonging to different chemical families: alcohols (methanol, ethanol, isopropanol, tert-butanol), ketones (acetone), nitriles (acetonitrile), and aromatic hydrocarbons (toluene). The conversion efficiency of these VOCs is studied as a function of the applied voltage on the micro-DBD (or electrical energy deposited in the plasma) and of the initial concentration of the molecules in the range from 1 ppm up to 3000 ppm (depending on the molecule), with the help of high-resolution real-time mass spectrometry Fourier transform ion cyclotron resonance associated to chemical ionisation (CI-FTICR) using H3O+ as precursor ion. A variety of by-products resulting from the conversion of VOCs are identified and quantified, emphasising that the micro-capillary plasma is able to induce a complex chemical reactivity. A qualitative analysis of the involved kinetics, based on the existing literature, reveals that helium species (ions and metastable states) and radicals coming from the dissociation of the water molecules (O and OH) are the most probable candidates to explain the formation of all compounds detected by the CI-FTICR apparatus. Quenching processes of the metastable He(23S) by the VOCs, leading to the dissociation of the molecules, are suggested to explain some of the experimental results. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the prediction of the wetting characteristics obtained from the equilibrium adsorption analysis using the Zeta adsorption isotherm approach with an experimental study. Water vapor's adsorption and wetting characteristics on a hydroxylated and nano-polished silica substrate were studied in near-equilibrium conditions at temperatures near 298 K. Using a UV–visible interferometer, water vapor adsorbate film thicknesses were measured and converted into amount adsorbed per unit area. The current results show that the wetting transition occurred at an average subcooling value of 0.39 K, less than the predicted value of 0.49 K. All the different experimental observations showed growth of film thickness as a function of subcooling value with a maximum film thickness of 12.6 nm. The analysis of the results further showed that the maximum stable film was in a metastable state that then condensed in a dropwise manner, if perturbed by increasing the subcooling. The study further revealed that the adsorbate is unstable after transitioning. The solid surface energy calculated by including the near-equilibrium observations was comparable and close to that of the equilibrium studies, thus supporting solid surface energy as a material property. [ABSTRACT FROM AUTHOR]

The study of the rare transitions that take place between long lived metastable states is a major challenge in molecular dynamics simulations. Many of the methods suggested to address this problem rely on the identification of the slow modes of the system, which are referred to as collective variables. Recently, machine learning methods have been used to learn the collective variables as functions of a large number of physical descriptors. Among many such methods, Deep Targeted Discriminant Analysis has proven to be useful. This collective variable is built from data harvested from short unbiased simulations in the metastable basins. Here, we enrich the set of data on which the Deep Targeted Discriminant Analysis collective variable is built by adding data from the transition path ensemble. These are collected from a number of reactive trajectories obtained using the On-the-fly Probability Enhanced Sampling flooding method. The collective variables thus trained lead to more accurate sampling and faster convergence. The performance of these new collective variables is tested on a number of representative examples. [ABSTRACT FROM AUTHOR]