Droplet Energy Harvesting System Based on Total-Current Nanogenerator.

The droplet-based nanogenerator (DNG) is a highly promising technology for harvesting high-entropy water energy in the era of the Internet of Things. Yet, despite the exciting progress made in recent years, challenges have emerged unexpectedly for the AC-type DNG-based energy system as it transitions from laboratory demonstrations to real-world applications. In this work, we propose a high-performance DNG system based on the total-current nanogenerator concept to address these challenges. This system utilizes the water-charge-shuttle architecture for easy scale-up, employs the field effect to boost charge density of the triboelectric layer, adopts an on-solar-panel design to improve compatibility with solar energy, and is equipped with a novel DC-DC buck converter as power management circuit. These features allow the proposed system to overcome the existing bottlenecks of DNG and empower the system with superior performances compared with previous ones. Notably, with the core architecture measuring only 15 cm × 12.5 cm × 0.3 cm in physical dimensions, this system reaches a record-high open-circuit voltage of 4200 V, capable of illuminating 1440 LEDs, and can charge a 4.7 mF capacitor to 4.5 V in less than 24 min. In addition, the practical potential of the proposed DNG system is further demonstrated through a self-powered, smart greenhouse application scenario. These demonstrations include the continuous operation of a thermohygrometer, the operation of a Bluetooth plant monitor, and the all-weather energy harvesting capability. This work will provide valuable inspiration and guidance for the systematic design of next-generation DNG to unlock the sustainable potential of distributed water energy for real-world applications.

Insights into Photogenerated Carrier Dynamics and Overall Water Splitting of the CrS3/GeSe Heterostructure.

Based on the nonadiabatic molecular dynamics (NAMD) simulations and the first-principles calculations, we explore the overall water-splitting schemes and the photogenerated carrier dynamics for two configurations (CG and CyG) of the CrS3/GeSe van der Waals heterostructures. The photocatalytic direct Z-schemes and carrier migration pathways for hydrogen and oxygen evolution reactions (HER/OER) are constructed based on the electronic properties. The solar-to-hydrogen efficiency (η'STH values) of the schemes can reach 10.60% and 10.17% and further rise under tensile strain. The NAMD results demonstrate similar transfer times of the electron/hole for HER/OER and more rapid electron-hole recombination in CG enables it to be superior to CyG in photocatalytic performance. Moreover, the Gibbs free energy indicates that both the HERs and OERs turn to spontaneously proceed with CG and CyG at pH = 0-12.37 and pH = 2.55-11.01, respectively. These facts reveal that the CrS3/GeSe heterostructure is promising in photocatalytic overall water splitting.

Enhancing Gating Performance in Organic Molecular Field-Effect Transistors by Introducing Polar Azulene Components.

Organic molecular field-effect transistors (FETs) are promising building components for future electronic circuits. Efficient control of charge transport properties is one key issue in the design of organic molecular FETs. In this study, we propose a redesign of a naphthalene-based FET by introducing two azulene components in opposite dipole moment directions. Using density functional theory combined with non-equilibrium Green's function, the simulated electronic transport characteristics reveal that the introduction of polar azulene components effectively narrows the frontier molecular orbitals gap, leading to an increase in the ON-state current. Meanwhile, the OFF-state current is significantly suppressed by highly localizing the dominant electronic transport channel. As a result, improved gate controllability is achieved with a higher ON-OFF current ratio, which is nearly seven times higher than that of the naphthalene-based FET device. These findings provide theoretical directions for future design of organic molecular FET devices with enhanced gating regulation efficiency.

The impact of non-adiabatic effects on reaction dynamics: a study based on the adiabatic and non-adiabatic potential energy surfaces of CaH2.

The two-state non-adiabatic potential energy matrices of the CaH2+ system are calculated via a diabatization approach by using a neural network model. Subsequently, the adiabatic and non-adiabatic potential energy surfaces (PESs) are constructed based on these non-adiabatic potential energy matrices. Furthermore, based on the adiabatic and non-adiabatic PESs, the Ca+(4s2S) + H2(X1Σ+g) → H(2S) + CaH+(X1Σ+) reaction is studied using the time-dependent wave packet method. Comparative analysis of the experimental and theoretical integral reaction cross-sections (ICSs) indicates that the maximum deviation between the results obtained from the adiabatic PES and the corresponding experimental value is 12.7 bohr2; in contrast, the maximum discrepancy between the theoretical result derived from the non-adiabatic PES and the experimental value is merely 0.42 bohr2. The potential well along the reaction path acts as a 'filter', selectively guiding intermediates with longer lifetimes in the potential well back to the reactant channel. This phenomenon indicates that the non-adiabatic effects significantly influence the reaction dynamics of the CaH2+ system.

Theoretical Prediction of Electrocatalytic Reduction of CO2 Using a 2D Catalyst Composed of 3 d Transition Metal and Hexaamine Dipyrazino Quinoxaline.

Transition metals and organic ligands combine to form metal-organic frameworks (MOFs), which possess distinct active sites, large specific surface areas and stable porous structures, giving them considerable promise for CO2 reduction electrocatalysis. In the present study, using spin polarisation density-functional theory, a series of 2D MOFs constructed from 3d transition metal and hexamethylene dipyrazoline quinoxaline(HADQ) were investigated. The calculated binding energies between HADQ and metal atoms for the ten TM-HADQ monolayers were strong sufficient to stably disperse the metal atoms in the HADQ monolayers. Of the ten catalysts tested, seven (Sc, Ni, Cu, Zn, Ti, V and Cr) exhibited high CO2 reduction selectivity, while Mn, Fe and Co required pH values above 2.350, 6.461 and 6.363, respectively, to exhibit CO2 reduction selectivity. HCOOH was the most important producer for Sc, Zn, Ni and Mn, while CH4 was the main producer for Ti, Cr, Fe and V. Cu and Co were less selective, producing HCHO, CH3 OH, and CH4 simultaneously at the same rate-determining step and limiting potential. The Cu-HADQ catalyst had a high overpotential for the HCHO product (1.022 V), while the other catalysts had lower overpotentials between 0.016 V and 0.792 V. Thus, these results predict TM-HADQ to show excellent activity in CO2 electrocatalytic reduction and to become a promising electrocatalyst for CO2 reduction.

The effect of the CPP size on the nonlinear optical properties of the new necklace-type molecules formed by carborane and [n]Cycloparaphenylenes(n = 8-11).

The new necklace-type molecules were formed by [8-13]CPP and carborane, which further manipulated the size of the macroring, revealing the effect of size on its luminescence behavior. In this work, the effects of ring size on the absorption spectrum, electron excitation and nonlinear optical properties of the compounds were investigated in detail, aiming to reveal an effective way to improve the optical properties of these necklace-type compounds. The absorption spectra of the compounds showed that the size of the CPP ring had little effect on the spectral shape and position, but the electron transition information showed that there were the significant charge transfer within the CPP ring and a gradual enhancement of interfragment charge transfer from the CPP ring to carborane. The increasing order of polarizability, first and second hyperpolarizability values of these compounds with the increase of CPP size indicated that increasing the size of the CPP ring was an effective way to increase the nonlinear optical properties of necklace-type molecules. Among the frequency dependent hyperpolarizability values, the γ(-ω;ω,0,0) value increased by a factor of 4 from complex 1 to 6 with the increase of CPP ring size, which indicated that increasing the size of the CPP ring was an effective way to increase the optical Kerr effect of necklace-type molecules. Therefore, these the new necklace-type nolecules formed by carborane and [n]Cycloparaphenylenes would be excellent nonlinear optical materials in the field of the all-optical switch.

Rare-earth metal-N6 centers in porous carbon for electrocatalytic CO2 reduction.

Single-atom catalysts fabricated using rare earth elements have emerged for electrocatalytic carbon dioxide reduction, but they need to be studied systematically and intensively. Herein, density functional theory was employed to determine the electrocatalytic CO2 reduction activity of rare earth-N6 porous carbon (Re = Ce, Nd, Sm, Eu, Gd, Tb, Er, Tm, Yb, and Lu) single-atom catalysts. The results revealed that the binding energy of the rare-earth atoms to the N6C monolayers in the ten studied Re-N6C monatomic catalysts is much more negative than the cohesion energy of the bulk rare-earth metal, which makes rare-earth atoms stably dispersed in the N6C skeleton. CO is the primary chemical product of electrocatalytic CO2 reduction by Ce, Eu, and Lu. The primary product of the six monatomic species, i.e., Nd, Sm, Tb, Er, Tm, and Yb, is HCOOH. The dominant product of Gd is CH4. The limiting potentials of these catalysts are in the range of 0.31-0.786 V and their overpotentials are in the range of 0.06-0.707 V, all of which are relatively low, showing that they are potential and promising electrocatalysts for CO2 reduction. Subsequently, Eu-N6C was experimentally synthesized and used for electrocatalytic CO2 reduction to obtain CO products, and the overpotential showed good agreement with the theoretically calculated values.

Effects of Inorganic Substitutions and Different Metal Electrode Materials on Electronic Transport Properties of Organic Molecular Devices.

Incorporating inorganic components into organic molecular devices offers one novel alternative to address challenges existing in the fabrication and integration of nanoscale devices. In this study, using a theoretical method of density functional theory combined with the nonequilibrium Green's function, a series of benzene-based molecules with group III and V substitutions, including borazine molecule and XnB3-nN3H6 (X = Al or Ga, n = 1-3) molecules/clusters, are constructed and investigated. An analysis of electronic structures reveals that the introduction of inorganic components effectively reduces the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, albeit at the cost of reduced aromaticity in these molecules/clusters. Simulated electronic transport characteristics demonstrate that XnB3-nN3H6 molecules/clusters coupled between metal electrodes exhibit lower conductance compared to prototypical benzene molecule. Additionally, the choice of metal electrode materials significantly impacts the electronic transport properties, with platinum electrode devices displaying distinct behavior compared to silver, copper, and gold electrode devices. This distinction arises from the amount of transferred charge, which modulates the alignment between molecular orbitals and the Fermi level of the metal electrodes by shifting the molecular orbitals in energy. These findings provide valuable theoretical insights for the future design of molecular devices incorporating inorganic substitutions.

Electron-phonon coupling, bipolar effects, and thermoelectric performance of the CuSbS2 monolayer.

The thermoelectric performance of the CuSbS2 monolayer is determined using the relaxation times obtained from electron-phonon coupling calculations and the transport properties of phonons and electrons. Based on the fully relaxed structure, the lattice thermal conductivity and the electronic transport coefficients are evaluated by solving the Boltzmann transport equation for phonons and electrons under relaxation time approximation, respectively. The tendencies of the transport coefficients depending on the carrier concentrations and temperatures are studied to understand the thermoelectric performance. Based on the bipolar effect, the transport coefficients and intrinsic carrier concentrations, we determined the dimensionless figure of merit ZT in the 300-800 K range. The results demonstrate that the CuSbS2 monolayer should be an p-type semiconductor, and the maximum ZT of 1.36 is obtained, indicating that the monolayer is a good candidate for high-temperature thermoelectric devices. Substantial bipolar effects are observed, and the ones in the x-direction are stronger in comparison to those in the y-direction, which is responsible for the smaller ZT in the x-direction.

Effect of intermolecular interaction of the charge-transfer complex between molecular "tweezers" and C60/C70 on second-order nonlinear optical properties.

To enhance understanding of the correlation between the intermolecular interaction and second-order nonlinear optical (NLO) properties, we studied a "molecular tweezer" with two corannulene substituents linked by a tetrahydro[5]helicene imide, which enabled highly sensitive and selective complexation of C60/C70 through convex-concave π-π interactions. The geometric structure, molecular orbitals, intermolecular interactions, electron absorption spectra and second-order NLO properties of the charge-transfer (CT) complexes formed by molecular tweezers and C60/C70 were studied by density functional theory. Larger fullerenes helped to increase the intermolecular interaction and CT, thereby increasing the first hyperpolarizabilities of CT complexes. Embedding of lithium ions helped to enhance the electron-absorption ability of fullerenes, thereby increasing the intermolecular interaction and intermolecular CT and, thus, enhancing their first hyperpolarizability significantly. Our data indicated that, through structure adjustment (including increasing the volume of fullerene and embedding alkali metal ions), we could enhance intermolecular interactions and improve intermolecular CT significantly. These actions could improve the second-order NLO properties of CT complexes.

The Resonance Raman Spectrum of Cytosine in Water: Analysis of the Effect of Specific Solute-Solvent Interactions and Non-Adiabatic Couplings.

In this contribution, we report a computational study of the vibrational Resonance Raman (vRR) spectra of cytosine in water, on the grounds of potential energy surfaces (PES) computed by time-dependent density functional theory (TD-DFT) and CAM-B3LYP and PBE0 functionals. Cytosine is interesting because it is characterized by several close-lying and coupled electronic states, challenging the approach commonly used to compute the vRR for systems where the excitation frequency is in quasi-resonance with a single state. We adopt two recently developed time-dependent approaches, based either on quantum dynamical numerical propagations of vibronic wavepackets on coupled PES or on analytical correlation functions for cases in which inter-state couplings were neglected. In this way, we compute the vRR spectra, considering the quasi-resonance with the eight lowest-energy excited states, disentangling the role of their inter-state couplings from the mere interference of their different contributions to the transition polarizability. We show that these effects are only moderate in the excitation energy range explored by experiments, where the spectral patterns can be rationalized from the simple analysis of displacements of the equilibrium positions along the different states. Conversely, at higher energies, interference and inter-state couplings play a major role, and the adoption of a fully non-adiabatic approach is strongly recommended. We also investigate the effect of specific solute-solvent interactions on the vRR spectra, by considering a cluster of cytosine, hydrogen-bonded by six water molecules, and embedded in a polarizable continuum. We show that their inclusion remarkably improves the agreement with the experiments, mainly altering the composition of the normal modes, in terms of internal valence coordinates. We also document cases, mostly for low-frequency modes, in which a cluster model is not sufficient, and more elaborate mixed quantum classical approaches, in explicit solvent models, need to be applied.

Efficient photocatalytic hydrogen evolution and CO2 reduction by HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures with direct Z-schemes.

The elaborate configuration of the heterostructure is crucial and challenging to achieve high solar-to-hydrogen efficiency or CO2 reduction efficiency . Here, we predict two heterostructures composed of HfSe2, ZrSe2, and GaAs3 monolayers. The maximum of 42.71%/35.12% with the heterostructures can be reached with the perfect match between the bandgap and band edges. The configurations of the heterostructures are discovered from 12 possible stacking types of the three monolayers. The formation energy, potentials of band edges, carrier mobilities, and optical absorption were used to identify the feasibility of the CO2 reduction reaction (CO2RR), the hydrogen evolution reaction (HER), and the oxygen evolution reaction (OER). The and based on overpotentials and bandgaps and the Gibbs free energies (ΔGs) are evaluated to quantificationally access the photocatalytic performance of the constructed heterostructures. The results demonstrate that high can be obtained for the solar photocatalytic Z-schemes with the HfSe2/GaAs3 and ZrSe2/GaAs3 heterostructures, and these values can be further enhanced through strain engineering. Moreover, small changes in ΔGs were observed for HER, OER, and CO2RR. Therefore, the two heterostructures have excellent performance in photocatalytic hydrogen evolution and CO2 reduction. The results of the electronic properties revealed that the delicate matching of the projected band edges of the monolayers in the heterostructures is responsible for the high photocatalytic performance.

Transverse electronic transport properties of single DNA nucleobase pairs between different electrode materials.

Detection of gene mutation through electronic transport properties measurements is an attractive research topic. For this purpose, we computed the current-voltage characteristics of adenine-thymine and guanine-cytosine nucleobase pairs, using a combination method of density-functional theory with non-equilibrium Green's function. Gene mutation was also simulated by structural change in nucleobase pairs by a double proton transfer mechanism. Four different metal electrodes were tested. Comparing the results, nucleobase pairs between platinum surfaces showed distinct electronic transport properties. Such as reverse rectifying direction and negative differential resistance behaviors. The discrepancy can be explained from series of electronic and structural analyses. All these results made identification of structural changes in individual DNA nucleobase pairs possible.

Molecular structure and spectroscopic properties of two radicals of C4H2N: a DFT study.

CONTEXT: The cyano propargyl radical (CH2C3N and HC3HCN) is important reaction intermediate in both combustion flames and extraterrestrial environments such as cold molecular clouds and circumstellar envelopes of carbon stars. The acquisition of spectroscopic constants and anharmonic effect facilitates a more in-depth study of this radical. However, the data available in the literature do not allow the precise predictions for it in the interstellar medium. In this work, complete spectroscopic parameters as well as anharmonic constants of two radicals of C4H2N have been evaluated by different DFT methods. The calculated results show that it is reasonable to study the molecular spectroscopic properties of C4H2N by wB97XD/6-311++G theoretical level. On this basis, the sextic centrifugal distortion constants, anharmonic constants, vibration-rotation interaction constants, and so on are predicted for the study of high-precision rovibrational spectrum. In addition, the relationship between the anharmonic effect and vibration mode of CH2C3N and HC3HCN and their infrared spectroscopic characteristics are discussed. METHODS: The calculation of the anharmonic force fields and spectroscopy properties was performed using B3LYP, B3PW91, CAM-B3LYP, and wB97XD methods combined with the 6-311++G and aug-ccpVTZ basis sets, respectively, by the Gaussian16 program suite. The IR spectra were performed with Multiwfn3.8.

Effects of Atypical Hydrogen Bonds and π-π Interactions on Nonlinear Optical Properties: Dimers of Triangular Structures Based on Perylene, Naphthalene, and Pyromellitic Diimides.

Nonlinear optical (NLO) materials have become important materials in the field of high-speed optical devices due to the changes in light absorption and refraction caused by the photoelectric field. Compounds tend to exist as aggregates rather than single molecules, so intermolecular interactions are crucial to the nature of aggregates. Therefore, to study the effects of intermolecular interactions on nonlinear optical properties, we use a dimer simplified model and adopt the methods of controlling variables, which are the different intermolecular interactions resulting from the different stacking patterns of dimers based on the same monomer structures (2PMDI-1NDI and 2NDI-1PDI). It is found that compared with dimers involving π-π interactions, dimers involving C-H···O interactions have shorter intermolecular distances, larger intermolecular interaction energies, and smaller highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps. Moreover, the C-H···O interactions are more conducive to the intermolecular charge transfers and more beneficial for increasing the nonlinear optical response values of aggregates with respect to π-π interactions. This work provides an important basis for the influence of intermolecular interactions on nonlinear optical properties.

Theoretical Simulations of Kinetic Isotope Effects on Decarboxylation of 3-Carboxybenzisoxazole.

Kinetic isotope effect values on the decarboxylation of 3-carboxybenzisoxazole have been computed using the second-order Kleinert's variational perturbation theory in the framework of Feynman's path integrals along with the potential energy surface obtained at the MP2/6-31+G(d) level. Good agreement with the experimental data was obtained, demonstrating that this novel computational approach for computing KIE values of organic reaction is a viable alternative to the traditional method employing the Bigeleisen equation and harmonic vibrational frequencies. Compared with the experimental measurements, consideration of anharmonicity and tunneling effects can significantly improve the calculated KIE values, reducing the root-mean-square deviation from 1.19 % for traditional method to 0.20 % for path-integral method.

The organic co-crystals formed using naphthalenediimide-based triangular macrocycles and coronene: intermolecular charge transfers and nonlinear optical properties.

Formation of organic co-crystals is an effective strategy to synthesize near infrared emission and nonlinear optical (NLO) materials, which often show "1 + 1 > 2" performance. Moreover, the crystallization process can be effectively regulated through supramolecular interactions; thus the properties of co-crystal materials can also be flexibly regulated. Here, in order to further understand the nature and formation mechanism of co-crystals from the perspective of theoretical research, we studied the structures, intermolecular interactions, absorption spectra, charge transfer (CT) characteristics and nonlinear optical (NLO) properties of the newly synthesized organic co-crystals formed between naphthalenediimide based triangles (NDI, acceptor) and coronene (COR, donor). According to the analysis of decomposition of intermolecular interaction energy, dispersion energy played a major role, so the co-crystal properties can be regulated by regulating the intermolecular dispersion energy. More importantly, the formation of co-crystals NDI-COR and NDI-2COR reduced the Egap values with respect to those of their components. And there was significant intermolecular CT from COR to NDI and the degree of CT in NDI-COR was larger than that in NDI-2COR, so that the αtot and γtot values of NDI-COR and NDI-2COR were significantly greater than those of their components. Thus, the NLO properties of organic co-crystals can be further improved by enhancing the electron-donating ability of the donor and the electron-withdrawing ability of the acceptor to enhance the degree of intermolecular interaction energy and CT.

Nonadiabatic Vibrational Resonance Raman Spectra from Quantum Dynamics Propagations with LVC Models. Application to Thymine.

We present a viable protocol to compute vibrational resonance Raman (vRR) spectra for systems with several close-lying and potentially coupled electronic states. It is based on the parametrization of linear vibronic coupling (LVC) models from time-dependent density functional theory (TD-DFT) calculations and quantum dynamics propagations of vibronic wavepackets with the multilayer version of the multiconfiguration time-dependent Hartree (ML-MCTDH) method. Our approach is applied to thymine considering seven coupled electronic states, comprising the three lowest bright states, and all vibrational coordinates. Computed vRR at different excitation wavelengths are in good agreement with the available experimental data. Up to 250 nm the signal is dominated by the lowest HOMO → LUMO transition, whereas at 233 nm, in the valley between the two lowest energy absorption bands, the contributions of all the three bright states, and their interferences and couplings, are important. Inclusion of solvent (water) effects improves the agreement with experiment, reproducing the coalescence of vibrational bands due to CC and C═O stretchings. With our approach we disentangle and assess the effect of interferences between the contribution of different quasi-resonant states to the transition polarizability and the effect of interstate couplings. Our findings strongly suggest that in cases of close-lying and potentially coupled states a simple inclusion of interference effects is not sufficient, and a fully nonadiabatic computation should instead be performed. We also document that for systems with strong couplings and quasi-degenerate states, the use of HT perturbative approach, not designed for these cases, may lead to large artifacts.

Spectroscopic constants and anharmonic force field of dithioformic acid and its isomers: a theoretical study.

The potential astronomical interest dithioformic acid (trans-HC(= S)SH) exists five isomers and has received considerable attention of astronomical observation in recent years. The different positions of H atoms of five isomers lead to diverse point groups, dipole moments, and spectroscopic constants. The anharmonic force field and spectroscopic constants of them are calculated using CCSD(T) and B3LYP employing correlation consistent basis sets. Molecular structures, dipole moments, rotational constants, and fundamental frequencies of trans-HC(= S)SH are compared with the available experimental data. The B3LYP/Gen = 5 and CCSD(T)/Gen = Q results can reproduce them well. Molecular structures, dipole moments, relative energies, spectroscopic constants of cis-HC(= S)SH, and dithiohydroxy carbene (DTHC) are also calculated. The new data obtained in this study are expected to guide the future high resolution experimental work and to assist astronomical search for CH2S2.

Aggregation behavior of partially contacted graphene sheets in six-carbon alkanes: all-atom molecular dynamics simulation.

Molecular dynamics simulations are used to investigate the aggregation of the cross-contacted and non-cross-contacted graphene sheets in n-hexane, 2,3-dimethylbutane, and cyclohexane solvents. The results show that the main driving force of the graphene aggregation is the interaction between the graphene sheets, and the interaction between solvent molecules also contributes to the aggregation slightly. The initial graphene configurations and the solvent molecule structures both have effects on the graphene aggregation speed. Specifically, the cross-contacted graphene sheets aggregate faster than the non-cross-contacted configuration, since the interaction between the graphene sheets is larger and the direction of this interaction is conducive to pushing away the solvent molecules adsorbed on the graphene surface. The graphene aggregation speed is larger in n-hexane mainly since the mobility of the solvent molecules is higher than the other two solvents, while the interaction between graphenes/solvents has little influence for the systems used in this work. This work provides useful insights into the graphene aggregation in the solvents with different initial graphene configurations and solvent molecule structures.