Vibronic and Environmental Effects in Simulations of Optical Spectroscopy.

Including both environmental and vibronic effects is important for accurate simulation of optical spectra, but combining these effects remains computationally challenging. We outline two approaches that consider both the explicit atomistic environment and the vibronic transitions. Both phenomena are responsible for spectral shapes in linear spectroscopy and the electronic evolution measured in nonlinear spectroscopy. The first approach utilizes snapshots of chromophore-environment configurations for which chromophore normal modes are determined. We outline various approximations for this static approach that assumes harmonic potentials and ignores dynamic system-environment coupling. The second approach obtains excitation energies for a series of time-correlated snapshots. This dynamic approach relies on the accurate truncation of the cumulant expansion but treats the dynamics of the chromophore and the environment on equal footing. Both approaches show significant potential for making strides toward more accurate optical spectroscopy simulations of complex condensed phase systems.

Hydration of TiO2 Facets Regulates As(III) Adsorption: DFT and DRIFTS Study.

Hydration of TiO2 facets controls the reactions occurring at the mineral-water interfaces. However, the underlying mechanism of the facet-dependent hydration and the effect of hydration on contaminant adsorption are still ambiguous. Herein, arsenite [As(III)] adsorption on hydrated {001}, {100}, {101}, and {201} TiO2 was explored by integrating multiple characterizations and density functional theory (DFT) calculations. Our macroscopic adsorption results show an As(III) adsorption density order of {201} > {100} > {101} > {001}, though As(III) on each facet formed a bidentate binuclear structure, as evidenced by the extended X-ray absorption fine structure analysis. The in situ diffuse reflectance infrared Fourier transform spectroscopy analysis identified distinctive surface hydroxyls on four-faceted TiO2 upon water adsorption. The hydrated surface regulated the subsequent As(III) adsorption, giving an As(III) adsorption energy order of {201} (-0.95 eV) < {100} (-0.38 eV) < {101} (-0.005 eV) < {001} (0.04 eV) according to DFT calculations. The As(III) adsorption energy on hydrated facets was linearly correlated with the macroscopical As(III) adsorption density (R2 = 0.99, p < 0.05), revealing that the impregnable water binding highly suppressed the exchange of As(III) molecules with adsorbed water. Our study provided a novel insight into the facet-dependent interfacial adsorption.

Hairpin-Structured Magnetic SERS Sensor for Tetracycline Resistance Gene tetA Detection.

Antibiotic resistance genes (ARGs) have become emerging environmental contaminants, and the effective on-site detection of ARGs is urgently needed. Herein, we constructed a hairpin-structured magnetic sensor for the analysis of a widespread ARG, tetA, using surface-enhanced Raman scattering (SERS). The SERS sensor was assembled by immobilizing core-satellite structured Fe3O4@SiO2-Au with single-stranded DNA in a folded hairpin structure. The SERS sensor exhibited good sensitivity and specificity for the detection of laboratory-synthesized tetA ssDNA fragments. In addition, this SERS strategy is the first of its kind to be employed for monitoring environmental samples in the field, with a limit of detection reaching as low as 25 copies µL-1. Univariate and multivariate linear regression equations verify the practicability of the SERS sensor for quantitative tetA determination, showing the prospect for an amplification-free alternative platform for sensitive and reliable on-site detection of ARGs in the environment.

Virtual Screening of Hole Transport, Electron Transport, and Host Layers for Effective OLED Design.

The alignment of energy levels within an OLED device is paramount for high efficiency performance. In this study, the emissive, electron transport, and hole transport layers are consecutively evolved under the constraint of fixed electrode potentials. This materials development strategy takes into consideration the full multilayer OLED device, rather than just individual components. In addition to introducing this protocol, an evolutionary method, a genetic algorithm (GA), is evaluated in detail to increase its efficiency in searching through a library of 30 million organic compounds. On the basis of the optimization of the variety of GA parameters and selection methods, an exponential ranking selection protocol with a high mutation rate is found to be the preferred method for quickly identifying the top-performing molecules within the large chemical space. This search through OLED materials space shows that the pyridine-based central core with acridine-based fragments are good target host molecules for common electrode materials. Additionally, weak electron-donating groups, such as naphthalene- and xylene-based fragments, appear often in the optimal electron-transport layer materials. Triphenylamine- and acridine-based fragments, due to their strong electron-donating character, were found to be good candidates for the hole-transport layer.

Temperature effects on adsorption and diffusion dynamics of CH3CH2(ads) and H3C-C≡C(ads) on Ag(111) surface and their self-coupling reactions: ab initio molecular dynamics approach.

Density functional theory (DFT)-based molecular dynamics (DFTMD) simulations in combination with a Fourier transform of dipole moment autocorrelation function are performed to investigate the adsorption dynamics and the reaction mechanisms of self-coupling reactions of both acetylide (H3C-C(ß)≡C(α) (ads)) and ethyl (H3C(ß)-C(α)H2(ads)) with I(ads) coadsorbed on the Ag(111) surface at various temperatures. In addition, the calculated infrared spectra of H3C-C(ß)≡C(α)(ads) and I coadsorbed on the Ag(111) surface indicate that the active peaks of -C(ß)≡C(α)- stretching are gradually merged into one peak as a result of the dominant motion of the stand-up -C-C(ß)≡C(α)- axis as the temperature increases from 200 K to 400 K. However, the calculated infrared spectra of H3C(ß)-C(α)H2(ads) and I coadsorbed on the Ag(111) surface indicate that all the active peaks are not altered as the temperature increases from 100 K to 150 K because only one orientation of H3C(ß)-C(α)H2(ads) adsorbed on the Ag(111) surface has been observed. These calculated IR spectra are in a good agreement with experimental reflection absorption infrared spectroscopy results. Furthermore, the dynamics behaviors of H3C-C(ß)≡C(α)(ads) and I coadsorbed on the Ag(111) surface point out the less diffusive ability of H3C-C(ß)≡C(α)(ads) due to the increasing s-character of Cα leading to the stronger Ag-Cα bond in comparison with that of H3C(ß)-C(α)H2(ads) and I coadsorbed on the same surface. Finally, these DFTMD simulation results allow us to predict the energetically more favourable reaction pathways for self-coupling of both H3C-C(ß)≡C(α)(ads) and H3C(ß)-C(α)H2(ads) adsorbed on the Ag(111) surface to form 2,4-hexadiyne (H3C-C≡C-C≡C-CH3(g)) and butane (CH3-CH2-CH2-CH3(g)), respectively. The calculated reaction energy barriers for both H3C-C≡C-C≡C-CH3(g) (1.34 eV) and CH3-CH2-CH2-CH3(g) (0.60 eV) are further employed with the Redhead analysis to estimate the desorption temperatures approximately at 510 K and 230 K, respectively, which are in a good agreement with the experimental low-coverage temperature programmed reaction spectroscopy measurements.

Universal scaling of transverse sound speed and its isomorphic property in Yukawa fluids.

Molecular dynamical simulations are performed to investigate the scaling of the transverse sound speed in two-dimensional (2D) and 3D Yukawa fluids. From the calculated diagnostics of the radial distribution function, the mean-squared displacement, and the Pearson correlation coefficient, the approximate isomorphic curves for 2D and 3D liquidlike Yukawa systems are obtained. It is found that the structure and dynamics of 2D and 3D liquidlike Yukawa systems exhibit the isomorphic property under the conditions of the same relative coupling parameter Γ/Γ_{m}=const. It is demonstrated that the reduced transverse sound speed, i.e., the ratio of the transverse sound speed to the thermal speed, is an isomorph invariant, which is a quasiuniversal function of Γ/Γ_{m}. The obtained isomorph invariant of the reduced transverse sound speed can be useful to estimate the transverse sound speed, or determine the coupling strength, with applications to dusty (complex) plasma or colloidal systems.

Axial H-Bonding Solvent Controls Inhomogeneous Spectral Broadening, While Peripheral H-Bonding Solvent Controls Vibronic Broadening: Cresyl Violet in Methanol.

The dynamics of the nuclei of both a chromophore and its condensed-phase environment control many spectral features, including the vibronic and inhomogeneous broadening present in spectral line shapes. For the cresyl violet chromophore in methanol, we here analyze and isolate the effect of specific chromophore-solvent interactions on simulated spectral densities, reorganization energies, and linear absorption spectra. Employing both chromophore and its condensed-phase environment control many spectral features, including the vibronic and inhomogeneous broadening present in spectral line shapes. For the cresyl violet chromophore in methanol, we here analyze and isolate the effect of specific chromophore-solvent interactions on simulated spectral densities, reorganization energies, and linear absorption spectra. Employing both force field and ab initio molecular dynamics trajectories along with the inclusion of only certain solvent molecules in the excited-state calculations, we determine that the methanol molecules axial to the chromophore are responsible for the majority of inhomogeneous broadening, with a single methanol molecule that forms an axial hydrogen bond dominating the response. The strong peripheral hydrogen bonds do not contribute to spectral broadening, as they are very stable throughout the dynamics and do not lead to increased energy-gap fluctuations. We also find that treating the strong peripheral hydrogen bonds as molecular mechanical point charges during the molecular dynamics simulation underestimates the vibronic coupling. Including these peripheral hydrogen bonding methanol molecules in the quantum-mechanical region in a geometry optimization increases the vibronic coupling, suggesting that a more advanced treatment of these strongly interacting solvent molecules during the molecular dynamics trajectory may be necessary to capture the full vibronic spectral broadening.

Color-Tunable Room-Temperature Phosphorescence from Non-Aromatic-Polymer-Involved Charge Transfer.

Polymeric room-temperature phosphorescence (RTP) materials especially multicolor RTP systems hold great promise in concrete applications. A key feature in these applications is a triplet charge transfer transition. Aromatic electron donors and electron acceptors are often essential to ensure persistent RTP. There is much interest in fabricating non-aromatic charge-transfer-mediated RTP materials and it still remains a formidable challenge to achieve color-tunable RTP via charge transfer. Herein, a charge-transfer-mediated RTP material by embedding quinoline derivatives within a non-aromatic polymer matrix such as polyacrylamide (PAM) or polyvinyl alcohol (PVA) is developed. Through-space charge transfer (TSCT) is achieved upon alkali- or heat treatment to realize a long phosphorescence lifetime of up to 629.90 ms, high phosphorescence quantum yield of up to 20.51%, and a green-to-blue afterglow for more than 20 s at room temperature. This color-tunable RTP emerges from a nonaromatic polymer to single phosphor charge transfer that has rarely been reported before. This finding suggests that an effective and simple approach can deliver new color-tunable RTP materials for applications including multicolor display, information encryption, and gas detection.

Safety factor diagnostic for tokamak core plasma from three-dimensional reconstruction of pellet ablation trail.

Using a stereo camera system, a new diagnostic for the safety factor of the core plasma based on the pellet ablation trail is applied on the Experimental Advanced Superconducting Tokamak (EAST). In EAST discharge No. 128 874, a shattered pellet injection system is applied to inject a shattered neon pellet into the EAST. Since the strong magnetic field in tokamaks binds the ablated pellet material, the orientation of the pellet ablation trail is the same as the local magnetic field direction. Thus, from the three-dimensional reconstruction result of the pellet ablation trail, the local safety factor q can be obtained. The motional Stark effect (MSE) diagnostic is applied to determine the safety factor q profile in this shot. The determined safety factor q results for this new diagnostic are in quantitative agreement with those from the MSE diagnostic with the mean relative difference of only 6.8%, confirming the effectiveness of this new diagnostic of the safety factor.

Chemical mechanism of surface-enhanced Raman scattering spectrum of pyridine adsorbed on Ag cluster: ab initio molecular dynamics approach.

The surface-enhanced Raman scattering (SERS) spectrum of pyridine adsorbed on Ag20 cluster (pyridine-Ag20 ) at room temperature is calculated by performing ab initio molecular dynamics simulations in connection with a Fourier transform of the polarizability autocorrelation function to investigate the static chemical enhancement behind the SERS spectrum. The five enhanced vibrational modes of pyridine, namely, υ6a, υ1, υ12, υ9a, and υ8a, can be assigned and identified by using a new analytical scheme, namely, single-frequency-pass filter, which is based on a Fourier transform filtering technique. To understand the factors evoking the enhancement in the SERS spectrum, the dynamic properties of molecular structures and charges for both of the free pyridine and adsorbed pyridine are analyzed. The calculated results indicate that the vibrational amplitudes of adsorbed pyridine are enhanced due to both of the electron transfer from pyridine to Ag20 cluster and the softening of pyridine bond. In addition, the N-Ag stretching within pyridine-Ag20 will couple with these five vibrational modes of pyridine. Consequently, the electron transfer between pyridine and Ag20 cluster induced by different molecular vibrational modes prompts the redistribution of electron density of pyridine. These factors collectively cause the noticeable change in polarizability during molecular vibrations and hence result in the enhancement of Raman peaks.

Observation of fast sound in two-dimensional dusty plasma liquids.

Equilibrium molecular dynamics simulations are performed to study two-dimensional (2D) dusty plasma liquids. Based on the stochastic thermal motion of simulated particles, the longitudinal and transverse phonon spectra are calculated, and used to determine the corresponding dispersion relations. From there, the longitudinal and transverse sound speeds of 2D dusty plasma liquids are obtained. It is discovered that, for wavenumbers beyond the hydrodynamic regime, the longitudinal sound speed of a 2D dusty plasma liquid exceeds its adiabatic value, i.e., the so-called fast sound. This phenomenon appears at roughly the same length scale of the cutoff wavenumber for transverse waves, confirming its relation to the emergent solidity of liquids in the nonhydrodynamic regime. Using the thermodynamic and transport coefficients extracted from the previous studies, and relying on the Frenkel theory, the ratio of the longitudinal to the adiabatic sound speeds is derived analytically, providing the optimal conditions for fast sound, which are in quantitative agreement with the current simulation results.

Adaptive ELM-Based Security Control for a Class of Nonlinear-Interconnected Systems With DoS Attacks.

This article is concerned with the output feedback security control of a class of high-order nonlinear-interconnected systems with denial-of-service (DoS) attacks, nonlinear dynamics, and exogenous disturbances. First, extreme learning machine (ELM) and adaptive techniques are adopted to approximate the unknown nonlinearities. Then, novel adaptive ELM-based nonlinear state observers with adaptive compensation functions are developed to estimate the unmeasurable states during DoS attacks under the influence of the disturbances. Further, by combining with the backstepping control and filtering techniques, adaptive ELM-based controllers are proposed to achieve uniformly ultimately bounded results based on the observation and adaption control signals under the influence of DoS attacks, nonlinear dynamics, and exogenous disturbances. Comparative studies are carried out to validate the effectiveness of the developed ELM-based adaptive observation and control strategies for two interconnected power systems.

Temperature dependence of vibrational modes of CH3CC(ads) and I(ads) coadsorbed on Ag(111): ab initio molecular dynamics approach.

Ab initio molecular dynamics simulations accompanied by a Fourier transform of the dipole moment (aligned perpendicular to the surface) autocorrelation function are implemented to investigate the temperature-dependent infrared (IR) active vibrational modes of CH3C(ß)C(α)(ads) and I(ads) when coadsorbed on an Ag(111) surface at 200 and 400 K, respectively. The analytic scheme of the Fourier transform of a structural coordinate autocorrelation function is used to identify two distinguishable IR active peaks of C(ß)C(α) stretching, which are characterized by two types of dynamic motion of adsorbed CH3C(ß)C(α)(ads) at 200 K, namely, the motion of the tilted CC(ß)C(α) axis and the motion of the stand-up CC(ß)C(α) axis. These two recognisable IR active peaks of C(ß)C(α) stretching are gradually merged into one peak as a result of the dominant motion of the stand-up CC(ß)C(α) axis as the temperature increases from 200 to 400 K. The calculated intensities of the IR active peaks of the asymmetrical deformation mode of CH3 and the asymmetrical stretching mode of CH3, with their dynamic dipole moments nearly perpendicular to the CC(ß)C(α) axis, become relatively weak; however, the symmetrical deformation mode of CH3 and the symmetrical stretching mode of CH3, with their dynamic dipole moments randomly directed away from the CC(ß)C(α) axis, will not have direct correspondence between the intensities of their IR active peaks and the angle between the Ag(111) surface and the CC(ß)C(α) axis as the temperature increases from 200 to 400 K. Finally, the increased flipping from the motion of the tilted CC(ß)C(α) axis to the motion of the stand-up CC(ß)C(α) axis followed by its diffusion, resulting from the increasing temperature from 200 to 400 K or even higher, seems to be the initial event that initiates the alkyne self-coupling reaction that leads to the final production of H3CCCCCCH3.

Shear softening and hardening of a two-dimensional Yukawa solid.

Langevin dynamical simulations are performed to study the elastic behaviors of two-dimensional (2D) solid dusty plasmas under the periodic shear deformation. The frequency- and strain-dependent shear moduli G(ω,γ) of our simulated 2D Yukawa solid are calculated from the ratio of the shear stress to strain in different orientations. The shear-softening and -hardening properties in different lattice orientations are discovered from the obtained G(ω,γ). The component of the elastic constant tensor corresponding to the shear deformation is also calculated, whose variation trend exactly agrees with the discovered shear-softening and -hardening features in different shear directions. It is also found that the shear modulus of the 2D Yukawa solid always increases monotonically with the frequency.

Erratum: Determination of viscosity in shear-induced melting two-dimensional dusty plasmas using Green-Kubo relation [Phys. Rev. E 103, 013211 (2021)].

This corrects the article DOI: 10.1103/PhysRevE.103.013211.

Adaptive NN-Based Consensus for a Class of Nonlinear Multiagent Systems With Actuator Faults and Faulty Networks.

This article addresses the problem of fault-tolerant consensus control of a general nonlinear multiagent system subject to actuator faults and disturbed and faulty networks. By using neural network (NN) and adaptive control techniques, estimations of unknown state-dependent boundaries of nonlinear dynamics and actuator faults, which can reflect the worst impacts on the system, are first developed. A novel NN-based adaptive observer is designed for the observation of faulty transformation signals in networks. On the basis of the NN-based observer and adaptive control strategies, fault-tolerant consensus control schemes are designed to guarantee the bounded consensus of the closed-loop multiagent system with disturbed and faulty networks and actuator faults. The validity of the proposed adaptively distributed consensus control schemes is demonstrated by a multiagent system composed of five nonlinear forced pendulums.

MOF Hybrid for Long-Term Pest Management and Micronutrient Supply Triggered with Protease.

Advanced intelligent systems for delivery of pesticides or fertilizers require formulations that allow for long-term efficacy. In this work, a metal-organic framework (MOF) hybrid was developed for long-term pest management and micronutrient supply. Zeolitic imidazolate framework-8 was fabricated for crop micronutrients (Zn2+) supply and insecticide dinotefuran (DNF) encapsulation. Polymethylmethacrylate was polymerized in situ to impart the MOF hybrid with sustained cargo delivery. Then, zein was introduced to facilitate protease-triggered cargo release associated with the microenvironment of pests and targeted release. The resulting MOF hybrid exhibited stimulus-responsive, slow-release behaviors. Sustained DNF delivery was achieved over a period of at least 32 days in soil. Compared with that of free DNF, the UV resistance of DNF in the MOF hybrid increased by nearly 10 times, and the insecticidal efficiency increased 33.3% with leaching treatment and 40.1% after incubating in a greenhouse for 14 days. This MOF hybrid provides a controlled, targeted, and sustained delivery formulation for long-term pest management and crop micronutrient supply and has huge application prospects in sustainable agriculture.

A Latent Profile Analysis of Chinese Physicians' Workload Tethered to Paperwork During Outpatient Encounters.

Background: Physician dissatisfaction with more time spent on related paperwork but less time available for direct interaction with patients is increasing internationally. Increased physician workload resulting from paperwork might negatively affect their interaction with patients and increase the risk for burnout. This study aimed to investigate the level of physician workload tethered to paperwork during outpatient encounters and explore its latent workload subgroups among Chinese physicians. Methods: A cross-sectional survey was conducted via online questionnaire primarily in 24 hospitals in 6 provinces in Eastern, Central, and Western China from November 2020 to February 2021. The Chinese physician mental workload scale developed by our research team was used for assessment of physician workload tethered to paperwork. Physicians were categorized into different subgroups of workload via latent profile analysis. Multinomial logistic regression was subsequently performed to examine how demographic variables differ among physicians belonging to different subgroups. Results: A total of 1,934 valid questionnaires were received. Chinese physicians reported medium levels of workload while performing non-physician-patient communication work tasks characterized by paperwork during outpatient encounters. Four latent workload subgroups were identified: "low workload group" (8.8%), "medium workload group" (34.0%), "high workload group" (42.1%) and "very high workload group" (15.1%). Compared with the other latent workload subgroups, physicians belonging to the "very high workload group" were more likely to be younger, married, those who had worse health status, lower educational levels and lower average monthly incomes, those who worked more years in the current institution, more hours per week and longer outpatient hours per week, and those who worked in public general hospitals, tertiary B hospitals and Obstetrics and Gynecology, and saw more than 50 outpatients per day, with more time spent on per patient. Conclusions: There exit four latent workload subgroups among Chinese physicians tethered to paperwork during outpatient encounters along with great individual variations among these subgroups. The characteristics of the latent "very high workload group" can help permit more targeted guidance for developing interventions with optimized human resource allocation to, in turn, increase the time available for direct interaction with patients, thereby resulting in improved quality of physician-patient interactions and decreased risk for physician burnout.

Comparison of Linear Response Theory, Projected Initial Maximum Overlap Method, and Molecular Dynamics-Based Vibronic Spectra: The Case of Methylene Blue.

The simulation of optical spectra is essential to molecular characterization and, in many cases, critical for interpreting experimental spectra. The most common method for simulating vibronic absorption spectra relies on the geometry optimization and computation of normal modes for ground and excited electronic states. In this report, we show that the utilization of such a procedure within an adiabatic linear response (LR) theory framework may lead to state mixings and a breakdown of the Born-Oppenheimer approximation, resulting in a poor description of absorption spectra. In contrast, computing excited states via a self-consistent field method in conjunction with a maximum overlap model produces states that are not subject to such mixings. We show that this latter method produces vibronic spectra much more aligned with vertical gradient and molecular dynamics (MD) trajectory-based approaches. For the methylene blue chromophore, we compare vibronic absorption spectra computed with the following: an adiabatic Hessian approach with LR theory-optimized structures and normal modes, a vertical gradient procedure, the Hessian and normal modes of maximum overlap method-optimized structures, and excitation energy time-correlation functions generated from an MD trajectory. Because of mixing between the bright S1 and dark S2 surfaces near the S1 minimum, computing the adiabatic Hessian with LR theory and time-dependent density functional theory with the B3LYP density functional predicts a large vibronic shoulder for the absorption spectrum that is not present for any of the other methods. Spectral densities are analyzed and we compare the behavior of the key normal mode that in LR theory strongly couples to the optical excitation while showing S1/S2 state mixings. Overall, our study provides a note of caution in computing vibronic spectra using the excited-state adiabatic Hessian of LR theory-optimized structures and also showcases three alternatives that are less sensitive to adiabatic state mixing effects.

Determination of viscosity in shear-induced melting two-dimensional dusty plasmas using Green-Kubo relation.

Langevin dynamical simulations of shear-induced melting two-dimensional (2D) dusty plasmas are performed to study the determination of the shear viscosity of this system. It is found that the viscosity calculated from the Green-Kubo relation, after removing the drift motion, well agrees with the viscosity definition, i.e., the ratio of the shear stress to the shear rate in the sheared region, even the shear rate is magnified ten times higher than that in experiments. The behaviors of shear stress and its autocorrelation function of shear-induced melting 2D dusty plasmas are compared with those of uniform liquids at the same temperatures, leading to the conclusion that the Green-Kubo relation is still applicable to determine the viscosity for shear-induced melting dusty plasmas.