A size-consistent multi-state mapping approach to surface hopping.

We develop a multi-state generalization of the recently proposed mapping approach to surface hopping (MASH) for the simulation of electronically nonadiabatic dynamics. This new approach extends the original MASH method to be able to treat systems with more than two electronic states. It differs from previous approaches in that it is size consistent and rigorously recovers the original two-state MASH in the appropriate limits. We demonstrate the accuracy of the method by applying it to a series of model systems for which exact benchmark results are available, and we find that the method is well suited to the simulation of photochemical relaxation processes.

A MASH simulation of the photoexcited dynamics of cyclobutanone.

In response to a community prediction challenge, we simulate the nonadiabatic dynamics of cyclobutanone using the mapping approach to surface hopping (MASH). We consider the first 500 fs of relaxation following photoexcitation to the S2 state and predict the corresponding time-resolved electron-diffraction signal that will be measured by the planned experiment. 397 ab initio trajectories were obtained on the fly with state-averaged complete active space self-consistent field using a (12,11) active space. To obtain an estimate of the potential systematic error, 198 of the trajectories were calculated using an aug-cc-pVDZ basis set and 199 with a 6-31+G* basis set. MASH is a recently proposed independent trajectory method for simulating nonadiabatic dynamics, originally derived for two-state problems. As there are three relevant electronic states in this system, we used a newly developed multi-state generalization of MASH for the simulation: the uncoupled spheres multi-state MASH method (unSMASH). This study, therefore, serves both as an investigation of the photodissociation dynamics of cyclobutanone, and also as a demonstration of the applicability of unSMASH to ab initio simulations. In line with previous experimental studies, we observe that the simulated dynamics is dominated by three sets of dissociation products, C3H6 + CO, C2H4 + C2H2O, and C2H4 + CH2 + CO, and we interpret our predicted electron-diffraction signal in terms of the key features of the associated dissociation pathways.

Partitioning of nutrient variation in alfalfa and corn silage by source on New York dairy farms.

Variation in feed components contributes to variation and uncertainty of diets delivered to dairy cows. Forages often have a high inclusion rate (50 to 70% of DM fed) and variable composition, thus are an important contributor to nutrient variability of delivered diets. Our objective was to quantify the variation and identify the main sources of variability in corn silage and alfalfa-grass haylage composition at harvest (fresh forage) and feed-out (fermented forage) on NY dairy farms. Corn silage and alfalfa-grass haylage were sampled on 8 NY commercial dairy farms during harvest in the summer and fall of 2020 and during their subsequent feed-out in the winter and spring of 2021. At harvest, a composite sample of fresh chopped forage of every 8-ha section of individual fields was collected from piles delivered for silo filling. During a 16-week feed-out period, 2 independent samples of each forage were collected 3 times per week. The fields-of-origin of each forage sample during feed-out were identified and recorded using silo maps created at filling. A mixed-model analysis quantified the variance of corn silage DM, NDF, and starch and haylage DM, NDF, and CP content. Fixed effects included soil type, weather conditions, and management practices during harvest and feed-out while random effects were farm, silo unit, field, and day. At harvest, between-farm variability was the largest source of variation for both corn silage and haylage, but within-farm sources of variation exceeded farm-to-farm variation for haylage at feed-out. At feed-out, haylage DM and NDF content had higher within-farm variability than corn silage. In contrast, corn silage starch showed higher within-farm variation at feed-out than haylage CP content. For DM content at feed-out, day-to-day variation was the most relevant source of within-farm variation for both forages. However, for the nutrient components at feed-out (NDF and CP for haylage; NDF and starch for corn silage) silo-to-silo variation was the largest source of variability. Weather conditions systematically explained a proportion of the farm-to-farm variability for both forages at harvest and feed-out. We concluded that because of the high farm-to-farm variation, corn silage and haylage must be sampled on individual farms. We also concluded that due to the high silo-to-silo variability, and the still significant day-to-day and field-to-field variability within-farm, corn silage and haylage should be sampled within individual silos to better capture changes in forage components at feed-out.

Recovering Marcus Theory Rates and Beyond without the Need for Decoherence Corrections: The Mapping Approach to Surface Hopping.

It is well-known that fewest-switches surface hopping (FSSH) fails to correctly capture the quadratic scaling of rate constants with diabatic coupling in the weak-coupling limit, as expected from Fermi's golden rule and Marcus theory. To address this deficiency, the most widely used approach is to introduce a "decoherence correction", which removes the inconsistency between the wave function coefficients and the active state. Here we investigate the behavior of a new nonadiabatic trajectory method, called the mapping approach to surface hopping (MASH), on systems that exhibit an incoherent rate behavior. Unlike FSSH, MASH hops between active surfaces deterministically and can never have an inconsistency between the wave function coefficients and the active state. We show that MASH not only can describe rates for intermediate and strong diabatic coupling but also can accurately reproduce the results of Marcus theory in the golden-rule limit, without the need for a decoherence correction. MASH is therefore a significant improvement over FSSH in the simulation of nonadiabatic reactions.

Fast Quasi-Centroid Molecular Dynamics for Water and Ice.

We describe how the fast quasi-centroid molecular dynamics (f-QCMD) method can be applied to condensed-phase systems by approximating the quasi-centroid potential of mean force as a sum of inter- and intramolecular corrections to the classical interaction potential. The corrections are found by using a regularized iterative Boltzmann inversion procedure to recover the inter- and intramolecular quasi-centroid distribution functions obtained from a path integral molecular dynamics simulation. The resulting methodology is found to give good agreement with a previously published QCMD dipole absorption spectrum for liquid water and satisfactory agreement for ice. It also gives good agreement with spectra from a recent implementation of CMD that uses a precomputed elevated temperature potential of mean force. Modern centroid molecular dynamics methods, therefore, appear to be reaching a consensus regarding the impact of nuclear quantum effects on the vibrational spectra of water and ice.

How Quantum is the Resonance Behavior in Vibrational Polariton Chemistry?

Recent experiments in polariton chemistry have demonstrated that reaction rates can be modified by vibrational strong coupling to an optical cavity mode. Importantly, this modification occurs only when the frequency of the cavity mode is tuned to closely match a molecular vibrational frequency. This sharp resonance behavior has proved to be difficult to capture theoretically. Only recently did Lindoy et al. [ Nat. Commun. 2023, 14, 2733] report the first instance of a sharp resonant effect in the cavity-modified rate simulated in a model system using exact quantum dynamics. We investigate the same model system with a different method, ring-polymer molecular dynamics (RPMD), which captures quantum statistics but treats dynamics classically. We find that RPMD does not reproduce this sharp resonant feature at the well frequency, and we discuss the implications of this finding for future studies of vibrational polariton chemistry.

Perturbatively corrected ring-polymer instanton theory for accurate tunneling splittings.

We introduce an approach for calculating perturbative corrections to the ring-polymer instanton approximation to tunneling splittings (RPI+PC) by computing higher-order terms in the asymptotic expansion in ℏ. The resulting method goes beyond standard instanton theory by using information on the third and fourth derivatives of the potential along the tunneling path to include additional anharmonic effects. This leads to significant improvements both in systems with low barriers and in systems with anharmonic modes. We demonstrate the applicability of RPI+PC to molecular systems by computing the tunneling splitting in full-dimensional malonaldehyde and a deuterated derivative. Comparing to both experiment and recent quantum mechanical benchmark results, we find that our perturbative correction reduces the error from -11% to 2% for hydrogen transfer and performs even better for the deuterated case. This makes our approach more accurate than previous calculations using diffusion Monte Carlo and path-integral molecular dynamics while being more computationally efficient.

Vibrational strong coupling in liquid water from cavity molecular dynamics.

We assess the cavity molecular dynamics method for the calculation of vibrational polariton spectra using liquid water as a specific example. We begin by disputing a recent suggestion that nuclear quantum effects may lead to a broadening of polariton bands, finding instead that they merely result in anharmonic red shifts in the polariton frequencies. We go on to show that our simulated cavity spectra can be reproduced to graphical accuracy with a harmonic model that uses just the cavity-free spectrum and the geometry of the cavity as input. We end by showing that this harmonic model can be combined with the experimental cavity-free spectrum to give results in good agreement with optical cavity measurements. Since the input to our harmonic model is equivalent to the input to the transfer matrix method of applied optics, we conclude that cavity molecular dynamics cannot provide any more insight into the effect of vibrational strong coupling on the absorption spectrum than this transfer matrix method, which is already widely used by experimentalists to corroborate their cavity results.

Application of Poly(caffeic acid) for the Extraction of Critical Rare Earth Elements.

Poly(caffeic acid) was synthesized and utilized for the extraction and determination of rare earth elements (REEs), thorium, and uranium. Oxidative polymerization of caffeic acid, a low-cost plant-based material, in the presence of ethylenediamine produced a granular, air-stable, and cross-linked polymer. The polymer is highly oxygenated and together with the amino group from ethylenediamine efficiently coordinates and preconcentrates these critical elements from aqueous media. Extraction was dependent on solution pH, amount of sorbent, and extraction time, while the concentration and flow rate of the desorption solution governed the recovery efficiency. Removal and recovery efficiencies greater than 98 and 90%, respectively, and low levels of detection ranging from 0.1 to 2.9 ng/L were achieved. Determination of these strategic elements in the presence of potentially interfering ions as well as in complex matrices such as well water and produced water samples also was demonstrated. The capacity of poly(caffeic acid) was determined with lanthanum as a representative REE to be 161.7 mg/g, establishing the promise of poly(caffeic acid) for larger-scale extractions in addition to the ability to screen sources for the presence of REEs.

Improved microcanonical instanton theory.

Canonical (thermal) instanton theory is now routinely applicable to complex gas-phase reactions and allows for the accurate description of tunnelling in highly non-separable systems. Microcanonical instanton theory is by contrast far less well established. Here, we demonstrate that the best established microcanonical theory [S. Chapman, B. C. Garrett and W. H. Miller, J. Chem. Phys., 1975, 63, 2710-2716], fails to accurately describe the deep-tunnelling regime for systems where the frequencies of the orthogonal modes change rapidly along the instanton path. By taking a first principles approach to the derivation of microcanonical instanton theory, we obtain an improved method, which accurately recovers the thermal instanton rate when integrated over energy. The resulting theory also correctly recovers the separable limit and can be thought of as an instanton generalisation of Rice-Ramsperger-Kassel-Marcus (RRKM) theory. When combined with the density-of-states approach [W. Fang, P. Winter and J. O. Richardson, J. Chem. Theory Comput., 2021, 17, 40-55], this new method can be straightforwardly applied to real molecular systems.

Explaining the Efficiency of Photosynthesis: Quantum Uncertainty or Classical Vibrations?

Photosynthetic organisms are known to use a mechanism of vibrationally assisted exciton energy transfer to efficiently harvest energy from light. The importance of quantum effects in this mechanism is a long-standing topic of debate, which has traditionally focused on the role of excitonic coherences. Here, we address another recent claim: that the efficient energy transfer in the Fenna-Matthews-Olson complex relies on nuclear quantum uncertainty and would not function if the vibrations were classical. We present a counter-example to this claim, showing by trajectory-based simulations that a description in terms of quantum electrons and classical nuclei is indeed sufficient to describe the funneling of energy to the reaction center. We analyze and compare these findings to previous classical-nuclear approximations that predicted the absence of an energy funnel and conclude that the key difference and the reason for the discrepancy is the ability of the trajectories to properly account for Newton's third law.

Unraveling the Complex Composition of Produced Water by Specialized Extraction Methodologies.

Produced water (PW), a waste byproduct of oil and gas extraction, is a complex mixture containing numerous organic solubles and elemental species; these constituents range from polycyclic aromatic hydrocarbons to naturally occurring radioactive materials. Identification of these compounds is critical in developing reuse and disposal protocols to minimize environmental contamination and health risks. In this study, versatile extraction methodologies were investigated for the untargeted analysis of PW. Thin-film solid-phase microextraction with hydrophilic-lipophilic balance particles was utilized for the extraction of organic solubles from eight PW samples from the Permian Basin and Eagle Ford formation in Texas. Gas chromatography-mass spectrometry analysis found a total of 266 different organic constituents including 1,4-dioxane, atrazine, pyridine, and PAHs. The elemental composition of PW was evaluated using dispersive solid-phase extraction followed by inductively coupled plasma-mass spectrometry, utilizing a new coordinating sorbent, poly(pyrrole-1-carboxylic acid). This confirmed the presence of 29 elements including rare earth elements, as well as hazardous metals such as Cr, Cd, Pb, and U. Utilizing chemometric analysis, both approaches facilitated the discrimination of each PW sample based on their geochemical origin with a prediction accuracy above 90% using partial least-squares-discriminant analysis, paving the way for PW origin tracing in the environment.

Fast quasi-centroid molecular dynamics.

We describe a fast implementation of the quasi-centroid molecular dynamics (QCMD) method in which the quasi-centroid potential of mean force is approximated as a separable correction to the classical interaction potential. This correction is obtained by first calculating quasi-centroid radial and angular distribution functions in a short path integral molecular dynamics simulation and then using iterative Boltzmann inversion to obtain an effective classical potential that reproduces these distribution functions in a classical NVT simulation. We illustrate this approach with example applications to the vibrational spectra of gas phase molecules, obtaining excellent agreement with QCMD reference calculations for water and ammonia and good agreement with the quantum mechanical vibrational spectrum of methane.

Synthesis and Characterization of Poly(pyrrole-1-carboxylic acid) for Preconcentration and Determination of Rare Earth Elements and Heavy Metals in Water Matrices.

Pyrrole was N-functionalized with solid carbon dioxide followed by chemical polymerization to create a new air-stable, granular, and water-insoluble sorbent, poly(pyrrole-1-carboxylic acid) (PPy-CO2). PPy-CO2 exhibited enhanced affinity for the sorption of metal ions compared to unfunctionalized PPy due to the incorporation of carboxylate functional groups directly onto the polymer backbone. As a freestanding sorbent material, immobilization to an additional solid support is not needed. Sorption, and therefore preconcentration, occurs simultaneously to achieve efficient removal and recovery of metal ions by a pH-dependent sorption-desorption mechanism. PPy-CO2 was evaluated on the analytical scale for the solid-phase extraction of a range of metal ions and found to efficiently preconcentrate rare earth elements (REEs), Th, and heavy metals (Cr, Fe, Cd, and Pb), which allowed quantitation by inductively coupled plasma mass spectrometry (ICP-MS). The impact of sorption parameters, such as solution pH, amount of sorbent, and sorption time, and the effect of desorption flow rate for recovery were investigated and optimized using ultrasound-assisted dispersive solid-phase extraction (UAD-SPE) with ICP-MS analysis. Maximum efficiency for sorption and recovery of most metal ions was achieved at a solution pH of 6.0, 10 mg of sorbent, a sorption time of 5 min, and desorption conditions of 1 mL of 2 M nitric acid applied at a flow rate of 0.25 mL min-1. Detection limits for REEs and Th ranged from 0.2-3.4 ng L-1 for REEs and Th and 0.9-5.7 ng L-1 for heavy metals. Linear ranges from 0.1-1000 µg L-1 for REEs and 0.1-500 µg L-1 for heavy metals and Th were also observed. PPy-CO2 successfully preconcentrated and facilitated the determination of the targeted metal ions in water matrices of varying complexity, including tap water, well water, river water, and produced water samples. These results indicate the potential application of PPy-CO2 for larger-scale recovery and removal of valuable or hazardous metal ions.

Humidicare - an implementation study of a novel HME safety device designed to prevent ventilator circuit occlusion due to inadvertent dual humidification.

Mechanical ventilation bypasses the protective mechanisms of the upper respiratory tract which are designed to heat and humidify inspired air to 37 °C and 44 mg H2O/L respectively. Artificial humidification systems are therefore incorporated into ventilation circuits to condition cold and dry medical gases before they reach the lower respiratory tract and cause patient harm. Commonly either a heat and moisture exchanger (HME) or a heated humidifier (HH) are utilised for this purpose, however the inadvertent simultaneous use of both devices within the same circuit can cause critical airway occlusion within 24 h. The Humidicare HME (Medovate, Cambridge, UK) is a safety engineered temperature-dependent warning system designed to activate when inadvertently placed into a warm circuit containing a HH. This study aimed to determine the efficacy of the Humidicare HME warning system in simulated clinical conditions. The threshold temperature for activation of the device was determined in a digital incubator, and the device was tested for efficacy with a HH present or absent from the breathing circuit. The device performed reliably and activated rapidly when required across all simulations. The Humidicare HME warning system is a simple and unobtrusive device which can effectively alert the operator to the error of dual humidification.

Fused Filament Fabrication (Three-Dimensional Printing) of Amorphous Magnesium Phosphate/Polylactic Acid Macroporous Biocomposite Scaffolds.

The ultimate goal of this paper is to develop novel ceramic-polymer-based biocomposite orthopedic scaffolds with the help of additive manufacturing. Specifically, we incorporate a bioceramic known as amorphous magnesium phosphate (AMP) into polylactic acid (PLA) with the help of the melt-blending technique. Magnesium phosphate (MgP) was chosen as the bioactive component as previous studies have confirmed its favorable biomaterial properties, especially in orthopedics. Special care was taken to develop constant diameter AMP-PLA composite filaments, which would serve as feedstock for a fused filament fabrication (FFF)-based three-dimensional (3D) printer. Before the filaments were used for FFF, a thorough set of characterization protocols comprising of phase analysis, microstructure evaluations, thermal analysis, rheological analysis, and in vitro degradation determinations was performed on the biocomposites. Scanning electron microscopy (SEM) results confirmed a homogenous dispersion of AMP particles in the PLA matrix. Rheological studies demonstrated good printability behavior of the AMP-PLA filaments. In vitro degradation studies indicated a faster degradation rate in the case of AMP-PLA filaments as compared to the single phase PLA filaments. Subsequently, the filaments were fed into an FFF setup, and tensile bars and design-specific macroporous AMP-PLA scaffolds were printed. The biocomposite exhibited favorable mechanical properties. Furthermore, in vitro cytocompatibility results revealed higher pre-osteoblast cell attachment and proliferation on AMP-PLA scaffolds as compared to single-phase PLA scaffolds. Altogether, this study provides a proof of concept that design-specific bioactive AMP-PLA biocomposite scaffolds fabricated by FFF can be potential candidates as medical implants in orthopedics.

Improved polymerization and depolymerization kinetics of poly(ethylene terephthalate) by co-polymerization with 2,5-furandicarboxylic acid.

Poly(ethylene terephthalate) (PET), known for its clarity, food safety, toughness, and barrier properties, is a preferred polymer for rigid packaging applications. PET is also one of the most recycled polymers worldwide. In light of climate change, significant efforts are underway to improve the carbon footprint of PET by synthesizing it from bio-based feedstocks. Often times, specific applications demand PET to be copolymerized with other monomers. This work focuses on copolymerization of PET with a bio-based co-monomer, 2,5-furandicarboxylic acid (FDCA) to produce the copolyester (PETF). We report the multifunction of FDCA to influence the esterification reaction kinetics and the depolymerization kinetics (via alkaline hydrolysis) of the copolyester PETF. NMR spectroscopy and titrimetric studies revealed that copolymerization of PET with different levels of FDCA improved the esterification reaction kinetics by enhancing the solubility of monomers. During the alkaline hydrolysis, the presence of FDCA units in the backbone almost doubled the PET conversion and monomer yield. Based on these findings, it is demonstrated that the FDCA facilitates the esterification, as well as depolymerization of PET, and potentially enables reduction of reaction temperatures or shortened reaction times to improve the carbon footprint of the PET synthesis and depolymerization process.