Intermolecular Polarization Research Articles

Weakly Solvating Electrolytes for Safe and Fast-Charging Sodium Metal Batteries.

Electrolytes for high-performance sodium metal batteries (SMBs) are expected to have high electrode compatibility, low solvation energy, and nonflammability. However, conventional flammable carbonate ester electrolytes show high Na+ desolvation energy and poor compatibility with sodium metal anodes, leading to slow Faradaic reactions and significant degradation of SMBs. Herein, we report a weakly solvating electrolytes (WSEs) design developed by an ionized ether-induced solvent molecule polarization strategy. The steric hindrance and electron-withdrawing effect of the pyrrolidine cation weaken the solvation ability of the ionized ether and enable carbonate ester with low solvation energy through intermolecular polarization interactions. It enables WSEs with fast Na+ migration kinetics and electric-field-reinforced cationic electrode/electrolyte interface, thereby promoting the stability and reversibility of SMBs even under high-charge-rate conditions. The Na||Na3V2(PO4)3 battery with ionized ether-based WSEs exhibits a capacity retention of 83.5% with an average Coulombic efficiency (CE) of 99.69% after 500 cycles at 10C. Furthermore, the Na||Na2Fe2(SO4)3 cells maintained 92.8% capacity retention after 1000 cycles at 5C with an average CE of 99.77% at a cutoff voltage of 4.5 V. The ionized ether also eliminates the fire and safety risks associated with WSEs. This work offers valuable insights into the design of WSEs for safe and high-performance sodium metal batteries.

Incorporating Noncovalent Interactions in Transfer Learning Gaussian Process Regression Models for Molecular Simulations.

FFLUX is a quantum chemical topology-based multipolar force field that uses Gaussian process regression machine learning models to predict atomic energies and multipole moments on the fly for fast and accurate molecular dynamics simulations. These models have previously been trained on monomers, meaning that many-body effects, for example, intermolecular charge transfer, are missed in simulations. Moreover, dispersion and repulsion have been modeled using Lennard-Jones potentials, necessitating careful parametrization. In this work, we take an important step toward addressing these shortcomings and show that models trained on clusters, in this case, a dimer, can be used in FFLUX simulations by preparing and benchmarking a formamide dimer model. To mitigate the computational costs associated with training higher-dimensional models, we rely on the transfer of hyperparameters from a smaller source model to a larger target model, enabling an order of magnitude faster training than with a direct learning approach. The dimer model allows for simulations that account for two-body effects, including intermolecular polarization and charge penetration, and that do not require nonbonded potentials. We show that addressing these limitations allows for simulations that are closer to quantum mechanics than previously possible with the monomeric models.

Multi-temperature charge scaling of ionic solvents: Disparate responses of thermodynamic properties

Charge scaling as a treatment to effectively include the intermolecular charge transfer and polarization effects is widely applied in molecular modelling of ionic solvents. While the charge scaling factor of 0.8 is picked as a generally applicable solution usable in many computational works, in this work based on extremely precise molecular simulations of bulk solvents and nonequilibrium Hamiltonian switching, we highlight the fact that the general 0.8 selection of the charge scaling factor could be a solution specific to the room-temperature condition that most ionic-liquids studies perform. When the environmental condition varies, this ‘general’ recommendation could sometimes lead to huge deviations. The situation is further complicated by the disparate responses of different properties (bulk density and solvation free energy) in the charge scaling space and along the temperature ladder. The driving force triggering the disparate responses could be attributed to the difference between interaction components involved in different thermodynamic properties, i.e., solvent–solvent interactions for bulk density and the additional solute–solvent interaction in the solvation process. A caution hinted by these observations is the necessity of condition- and property-specific parameter adjustment in practical situations.

Modeling of the Hydrogen Bond-Induced Frequency Shifts of the HOH and HOD Bending Modes of Water.

The intramolecular bending mode of water is a possible useful probe of the hydrogen-bond situations in aqueous systems, but the behavior of its frequency and intensity should be further elucidated for better understanding on its nature and, hence, for its better utilization as a probe. Here, an analysis toward this goal is conducted by doing theoretical calculations on molecular clusters of normal isotopic and deuterated species of water and examining the correlations among the vibrational, structural, and electrostatic properties. It is shown that electrostatic interactions, particularly both of the in-plane components of the electric field along the OH bond and perpendicular to it, play a major role in controlling the hydrogen bond-induced shifts of the force constant, but additional factors, including the intermolecular structural and/or charge-transfer properties, are also important. Models of the hydrogen bond-induced shifts of the force constant are presented in a form that may be combined with classical molecular dynamics. With regard to the infrared intensity changes, it is shown on the basis of the electron density analysis that the intermolecular charge flux and polarization effect play an important role, depending on the angular characteristics of the hydrogen bond.

The Impact of Polymorphism on Charge Transport Properties for Pyrene-FxTCNQ Cocrystals

Research on the charge transport properties of organic semiconductor materials is crucial for the development of organic sensors. In this paper, we investigated the charge transport properties of pyrene-TCNQ, pyrene-F2TCNQ, and pyrene-F4TCNQ cocrystals using the quantum nuclear tunneling model and Monte Carlo simulations to calculate charge mobility. At room temperature, we observed hole mobility values is 0.658 cm2V-1s-1 and electron mobility values is 1.492 cm2V-1s-1, respectively, for pyrene-TCNQ. As the number of F atoms in TCNQ increases, we observed an increase in both hole and electron mobility. Our results showed that the electron to hole mobility ratio was approximately 2.2 for pyrene-TCNQ, 0.6 for pyrene-F2TCNQ, and 0.5 for pyrene-F4TCNQ. Our findings suggest that the introduction of F atoms causes changes in the TCNQ molecular structure, cocrystal stacking mode, adjacent molecular distance, and intermolecular polarization. These changes lead to a modification of the reorganization energy and transfer integrals, ultimately affecting charge transport. Additionally, our results showed that transport along the π-π direction in the three cocrystals exhibited strong anisotropic characteristics, which were much larger than those observed in the other two directions.

Preparation and characterization of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals by physical vapour transport (PVT) technique

Good quality of N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals (space group Pna21, point group mm2) having different morphologies were successfully grown from vapour phase for the first time by physical vapour transport technique under predefined supersaturation conditions. BNA single crystals of different morphologies resulted at different supersaturation conditions: prismatic (σ = 0.0218 to 0.1553), columnar (σ = 0.1553 to 0.4652), needle (σ = 0.4652 to 0.7245), fine-needle (σ = 0.7245 to 0.9166) and dendritic (σ = 0.9166 to 0.9729). The predicted theoretical morphologies using BFDH, and attachment energy models are in line with the experimental morphologies. The slice thickness, slice energy, attachment energy and anisotropic growth factor of different faces were determined which reveals that {020} are the slow-growing and morphologically important facets amongst others present in the grown BNA single crystal. Fast growth along ‘+c’ direction and no growth along ‘-c’ direction was identified due to the supersaturation-dependant anisotropic growth nature of BNA. Crystal purity and quality are confirmed by single crystal X-ray diffraction study. In addition, the role of intermolecular interactions, electrostatic, polarization, repulsion and dispersion energy components involved in the crystal packing to stabilize the BNA single crystal were characterized by the Crystal Explorer 17.5 software. Computed energy frameworks confirm that the dispersion energy component is predominantly contributing to the crystal packing than the Coulombic interaction energies.

QMrebind: incorporating quantum mechanical force field reparameterization at the ligand binding site for improved drug-target kinetics through milestoning simulations.

Understanding the interaction of ligands with biomolecules is an integral component of drug discovery and development. Challenges for computing thermodynamic and kinetic quantities for pharmaceutically relevant receptor-ligand complexes include the size and flexibility of the ligands, large-scale conformational rearrangements of the receptor, accurate force field parameters, simulation efficiency, and sufficient sampling associated with rare events. Our recently developed multiscale milestoning simulation approach, SEEKR2 (Simulation Enabled Estimation of Kinetic Rates v.2), has demonstrated success in predicting unbinding (koff) kinetics by employing molecular dynamics (MD) simulations in regions closer to the binding site. The MD region is further subdivided into smaller Voronoi tessellations to improve the simulation efficiency and parallelization. To date, all MD simulations are run using general molecular mechanics (MM) force fields. The accuracy of calculations can be further improved by incorporating quantum mechanical (QM) methods into generating system-specific force fields through reparameterizing ligand partial charges in the bound state. The force field reparameterization process modifies the potential energy landscape of the bimolecular complex, enabling a more accurate representation of the intermolecular interactions and polarization effects at the bound state. We present QMrebind (Quantum Mechanical force field reparameterization at the receptor-ligand binding site), an ORCA-based software that facilitates reparameterizing the potential energy function within the phase space representing the bound state in a receptor-ligand complex. With SEEKR2 koff estimates and experimentally determined kinetic rates, we compare and interpret the receptor-ligand unbinding kinetics obtained using the newly reparameterized force fields for model host-guest systems and HSP90-inhibitor complexes. This method provides an opportunity to achieve higher accuracy in predicting receptor-ligand koff rate constants.

A scheme for rapid evaluation of the intermolecular three-body polarization effect in water clusters.

The ability to accurately and rapidly evaluate the intermolecular many-body polarization effect of the water system is very important for computer simulations of biomolecule in aqueous. In this paper, a scheme is proposed based on the polarizable dipole-dipole interaction model and used to rapidly estimate the intermolecular many-body polarization effect in water clusters. We use a bond-dipole-based polarization function to evaluate the polarization energy. We regard two OH bonds of a water molecule as two bond-dipoles and set the permanent OH bond-dipole moment of a water molecule to be 1.51 Debye. We estimate the induced OH bond-dipole moment via a simple formula in which only one correction factor is needed. This scheme is then applied to tens of water clusters to calculate the three- and four-body interaction energies. The three-body interaction energies of 93 water clusters produced by our scheme are compared with those produced by the counterpoise-corrected CCSD(T)/aug-cc-pVDZ, MP2/aug-cc-pVDZ, M06-2X/jul-cc-pVTZ methods, by the AMOEBApro13, iAMOEBA, AMOEBA+, AMOEBA+(CF) methods, and by the MB-pol method. The four-body interaction energies of 47 water clusters yielded by our scheme are compared with those yielded by the counterpoise-corrected MP2/aug-cc-pVDZ and M06-2X/ jul-cc-pVTZ methods, by the AMOEBApro13, AMOEBA+, AMOEBA+(CF) methods, and by the MB-pol method. The comparison results show that the scheme proposed in this paper can reproduce the counterpoise-corrected CCSD(T)/aug-cc-pVDZ three-body interaction energies and reproduce the counterpoise-corrected MP2/aug-cc-pVDZ four-body interaction energies both accurately and efficiently. We anticipate the scheme proposed here can be useful for computer simulations of liquid water and aqueous solutions.

Role of embedding choline chloride-urea deep eutectic solvent on biomass-derived porous activated carbon in its capacitive deionization performance

Capacitive deionization (CDI) is a propitious desalination technique for medium and large-scale applications. The CDI cell performance is primarily controlled by the electrode material characteristic. Beyond the classic electro-sorption phenomenon, assistive separation mechanisms may be incorporated through the surface functionality of the electrode technology to build on the salt removal efficiency of the CDI system. Herein, we report on the impact of modifying biomass-derived porous activated carbon (AC-FB) electrodes with a hydrophilic deep eutectic solvent (DES), such as choline chloride-urea (ChCl-U) to introduce extra ion-dipole interaction sites through its rich hydrogen bonding network. The HR-transmission electron microscopy evidences the presence of DES on the sample surface. The thermogravimetric analysis and water contact angle measurements were done on the AC-FB and AC-FB-DES electrode to confirm the successful embedding of DES into the activated carbon (AC). In this symmetric configuration, the Na+ and Cl− ions are accommodated by the modified layer at the AC-FB-DES electrode. The electrochemical properties of the electrode were analyzed using CV and EIS analysis. The AC-FB-DES showed an 85% enhancement of removal percent compared to the plain AC-FB at 1.2 V in a 600 mg L−1 NaCl solution, despite that it shows a 40% drop in the specific capacitance compared to that of the AC-FB at a scan rate of 10 mV s−1. It is believed that upon applying potential, the rearrangement in the layered structure of urea–choline chloride at the electrified interface of the AC-FB electrode provides electro-induced active sites which enhance both CDI kinetics and overall ions removal. It is also believed that embedding DES on the AC-FB enhances the electro-adsorption performance of the AC by modifying the electrical double layer structure at the interfaces by introducing extra intermolecular interactions and surface polarization that play a synergistic role in the salt removal process.

Beyond multipolar pseudoatom transferability: accounting for intermolecular polarization effects in protein–ligand complexes

Beyond multipolar pseudoatom transferability: accounting for intermolecular polarization effects in protein–ligand complexes

Strong intermolecular polarization to boost polysulfide conversion kinetics for high-performance lithium–sulfur batteries

In situ Raman analysis decoupling the polysulfides conversion kinetics reveals that the rate-limiting process of Li2S4 reduction is eliminated due to the CoIn2S4 induced intermolecular polarization.

Effect of Coulomb interaction on the second-order nonlinear optical and magneto-optical properties of the endohedral La@C82 crystal with spatial dispersion

Using the Hartree-Fock single-excitation configuration interaction (CI) model, the second- order nonlinear optical dielectric tensor, refractive index, reflectivity, circular dichroism (CD), birefringence coefficient (θ) and the effects of spatial dispersion of the simple cubic (sc) phase of the La@C82 crystal are calculated. It is shown that the intermolecular polarization interaction has significant effects on the nonlinear properties of the endohedral fullerenes, and that, in some contrast to other organic species, nondipolar contributions to this interaction are important. The spectral shapes of the second-order nonlinear dielectric tensor of the La@C82 crystal turn out to be determined mainly by the geometrical distributions of the pentagons in the fullerene structures. Our results on the effect of spatial dispersion show that the nonlinear refractive index and reflectivity of the La@C82 crystal in the energy range 0.3–6 eV have sharp structures in each band.

A unified mechanism for ice and water electrical conductivity from direct current to terahertz.

Knowledge of the electrical properties of liquid and solid water is extremely important for a detailed understanding of their structures. Though the macroscopic parameters differ, ice and water still have much in common from the dielectric spectroscopy viewpoint and should thus be considered on the same footing for the study of their electrical properties. In this work, we treat the complete dielectric spectra of ice and water, covering fourteen orders in frequency magnitude. Introducing the notion of 'excess proton gas' we explain the similarities between ice and water, and derive a model which links together the infrared vibrations and the static conductivity and dielectric constant. This model provides a very good description of spectra up to 10 THz and reproduces well the temperature dependence of the dielectric constant for both ice and water. A new intermolecular polarization mechanism suitable for ice and water provides good insights for the understanding of their electrical properties.

Atomistic Insight into the Electrochemical Double Layer of Choline Chloride-Urea Deep Eutectic Solvents: Clustered Interfacial Structuring.

Green, stable, and wide electrochemical window deep eutectic solvents (DESs) are ideal candidates for electrochemical systems. However, despite several studies of their bulk properties, their structure and properties under electrified confinement have barely been investigated, which has hindered widespread use of these solvents in electrochemical applications. In this Letter, we explore the electrical double layer structure of 1:2 choline chloride-urea (Reline), with a particular focus on the electrosorption of the hydrogen bond donor on a graphene electrode using atomistic molecular dynamics simulations. We discovered that the interface is composed of a mixed layer of urea and counterions followed by a mixed charged clustered structure of all of the Reline components. This interfacial structuring is strongly dependent on the balance between intermolecular interactions and surface polarization. These results provide new insights into the electrical double layer structure of a new generation of electrolytes whose interfacial structure can be tuned at the molecular level.

On the Molecular Origin of Charge Separation at the Donor–Acceptor Interface

AbstractFullerene‐based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor–acceptor (D–A) interface. Model systems comprised of polythiophene‐based donor and rylene diimide‐based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct‐contact intermolecular polarization play in establishing a driving force (energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules.

A new approach for chemical reaction simulation of rarefied gas flow by DSMC method

Present study concerns the development of a new approach for chemical reaction modelling in DSMC technique. The conventional quantum-kinetic (QK) method based on the VHS collision model is usually applied by the DSMC algorithm to simulate chemical reactions in rarefied gas flowfield. In this paper, a modified quantum-kinetic model (MQK) is presented to remove some limitation of the QK chemical model. The MQK method uses the GSS collision model based on the Stockmayer potential function which can capture both the attractive and repulsive intermolecular forces and polarization effect of the molecules in the reactive flow. To investigate the accuracy and capability of the proposed model, firstly, dissociation of the nitrogen (non-polar gas) and water vapour (polar gas) are simulated in a single cell DSMC for equilibrium and non-equilibrium conditions. The results of the MQK are assessed with those of the QK methods, analytical models and experimental data. Secondly, dissociation of these two types of gases is studies in the rarefied gas flowfield along the stagnation line of a typical hypersonic atmospheric blunt body problem. The flowfield properties including the density, velocity, transient, vibrational and total temperature along the stagnation line and surface properties including the surface pressure and heatflux at the stagnation point obtained by the MQK model are compared with results of the QK method and available analytical and experimental data. The results show that the MQK model provides more accurate results when the polarization effects and both the attractive-repulsive intermolecular forces are dominant especially at high temperature. Also, comparison of the computational cost between two models indicates higher efficiency using the proposed method rather than the QK model due to reduction of number of the collision pairs.

Performance of density-functional tight-binding models in describing hydrogen-bonded anionic-water clusters.

Density-functional tight-binding (DFTB) models are computationally efficient approximations to density-functional theory that have been shown to predict reliable structural and energetic properties for various systems. In this work, the reliability and accuracy of the self-consistent-charge DFTB model and its recent extension(s) in predicting the structures, binding energies, charge distributions, and vibrational frequencies of small water clusters containing polyatomic anions of the Hofmeister series (carbonate, sulfate, hydrogen phosphate, acetate, nitrate, perchlorate, and thiocyanate) have been carefully and systematically evaluated on the basis of high-level ab initio quantum-chemistry [MP2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVQZ] reference data. Comparison with available experimental data has also been made for further validation. The self-consistent-charge DFTB model, and even more so its recent extensions, are shown to properly account for the structural properties, energetics, intermolecular polarization, and spectral signature of hydrogen-bonding in anionic water clusters at a fraction of the computational cost of ab initio quantum-chemistry methods. This makes DFTB models candidates of choice for investigating much larger systems such as seeded water droplets, their structural properties, formation thermodynamics, and infrared spectra.

A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. The case of Na+in aqueous solution

The (23)Na quadrupolar coupling constant of the Na(+) ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na(+) ions in solution are found to differ significantly.

Sheet-Type Flexible Organic Active Matrix Amplifier System Using Pseudo-CMOS Circuits With Floating-Gate Structure

We successfully fabricated a large-area flexible strain-sensing system based on a 2-D array of organic self-bias-feedback amplifier with a signal gain of 400. The amplifier system consists of three layers: a self-assembled monolayer (SAM) capacitor matrix, a 2-D array of organic pseudo-CMOS inverters with a floating-gate structure using SAM gate dielectric, and an active matrix of organic thin-film transistors. The amplifier sheet comprises 8 × 8 amplifier cells, with an effective size of 7 × 7 cm2. The organic transistors exhibit a mobility of 1.7 cm2/V·s in the saturation regime at an operation voltage of 2 V. A strain sensor is made of a polymeric piezoelectric [polyvinylidene difluoride (PVDF)] sheet. When a cell of the PVDF sheet is touched (that is, when mechanical pressure is applied), a small signal is generated by intermolecular polarization in the PVDF. These signals are amplified by the organic amplifier circuits from 10 to 150 mV.

Tuning interchain and intrachain interactions in polyfluorene copolymers

We study how intermolecular interactions, conformational changes, and polarization effects control the nature of the electronic excitations in conjugated polymer blends. Quantum-chemical calculations and high-pressure photoluminescence experiments are used to assess these effects in polyfluorene-based donor--acceptor systems. The redshift of charge-transfer--like excitations usually observed under pressure is found to arise primarily from the reduced interchain distance; the corresponding shift of bulk excitons is equally sensitive to the interchain spacing and planarization alterations. Intermolecular charge-transfer states are shown to have shorter radiative lifetimes and higher oscillator strengths at high pressure. In contrast, intramolecular bulk excitons build up interchain charge-transfer character and lose oscillator strength and radiative efficiency with increasing pressure.