Force Field Method Research Articles

Intercalation of atorvastatin and valsartan into Mg[sbnd]Al layered double hydroxide host using a restacking procedure

Anionic drugs very poorly soluble in water, namely antidyslipidemic atorvastatin and antihypertensive valsartan were intercalated into MgAl LDH host using a restacking procedure, when the drugs, dissolved in ethanol, were added to aqueous dispersion of LDH nanosheets, prepared by direct coprecipitation of Mg and Al nitrates in excess of aqueous ammonia solution under nitrogen. Despite the large size of intercalated molecules, the products with high drug loading were obtained; the content 75.8 wt% of atorvastatin and 43.7 wt% of valsartan corresponded to 100 and 60% of the LDH anion exchange capacity, respectively. A marked increase in d003 basal spacing from 0.876 to 3.808 and 2.068 nm observed in powder XRD patterns of the LDH intercalated with atorvastatin and valsartan, respectively, confirmed the intercalation of both drugs into the LDH interlayer. The computational modeling applying the force field methods was used to calculate the most probable arrangement of the interlayer components at the atomic scale through energy minimization. The final models showed good agreement between the calculated and experimentally determined d003 basal spacing values. Results of the molecular modeling confirmed weak electrostatic interactions between LDH layers and terminal carboxyl groups in the drug molecules, together with bonding between the valsartan tetrazole rings and the LDH layers. Such interactions accompanied by deprotonation of carboxyl groups and tetrazole rings in the intercalated products were indicated by the FTIR and NMR measurements. The intercalation of drugs into LDH host slightly affected their back-release in aqueous media. In the phosphate buffer, slower atorvastatin release from the intercalated product compared to the sample containing atorvastatin calcium salt was observed, whereas enhanced valsartan release from the intercalated sample was found in the diluted HCl. The measured release profiles corresponded to the pseudo-second-order kinetics, indicating an intraparticle diffusion as the rate-limiting step.

How herbicides like atrazine and diuron interact with the spiral halloysite structure

The spiral tubular morphology of the halloysite mineral presents an interesting opportunity for pollutant remediation: a large specific surface area, porosity, high adsorption capacity, bivalent adsorbancy, and colloidal behaviour. Two worldwide used herbicides are atrazine and diuron, which have shown harmful impacts on the environment and fauna, including humans. Therefore, both herbicides were studied to test their interactions on the halloysite tubular structure. Force field methods using the COMPASS force field were applied to perform the geometry optimisation and molecular dynamics on the atrazine/diuron-halloysite models. The models were prepared with different herbicide loading ratios on the inner and outer parts of the halloysite structure to find the preferable interacting surface. The simulation showed that both halloysite surfaces could interact with atrazine and diuron molecules. Further, the herbicides’ arrangement on the surfaces depends on the herbicide’s concentration and subsequently on their mutual interactions. The inner surface of the halloysite showed stronger interactions with both herbicides than the outer surface, and especially with diuron (e.g., binding energies per herbicide molecule for atrazine and diuron were –115 ± 2 and –130 ± 3 kJ·mol−1, respectively). Increasing herbicide concentration on the inner surface is limited by free space, and the interaction capacity becomes gradually saturated both for atrazine and for diuron.

Lithium Dissolution and SEI Formation on Lithium Metal Anodes: Electrolyte and Surface Effects

The lithium metal battery (LMB) rises as one of the most promising energy storage alternatives primarily due to the lithium metal’s high theoretical specific capacity (3860 mAh/g vs. 372 mAh/g for graphite) and high achievable operation voltage [1, 2]. However, and regardless of the coupling cathode electrode, one of the main challenges before the practical application of LMBs comes down to engineering electrolyte formulations compatible with lithium metal to eliminate dendrite formation and the uncontrolled loss of electrolyte and active lithium by forming a robust, ionic-conductive, and electron insulating, solid electrolyte interphase (SEI).Any improvement of the electrolyte/lithium metal interface passes through a thorough understanding of the reaction mechanisms behind the electrolyte degradation and the subsequence formation of the SEI. Characterizing this interface via experimental techniques is a challenge because of its delicate nature and simultaneous presence of liquid and solid phases. Here, we successfully narrowed this gap via computational modeling by using a recently introduced hybrid ab initio and reactive molecular dynamics (HAIR) scheme that uses in sequence the ab-initio molecular dynamics (AIMD) and the reactive force field (ReaxFF) methods to extend the time window achievable with the AIMD method alone. We performed a series of HAIR calculations with multiple electrolytes formulations on a lithium metal slab (Li(100)) with varying electrolyte/anode (E/A) ratios to evaluate the impact of the lithium salt concentration, type of solvent, presence of a diluent, and lithium thickness on the rate of electrolyte depletion, lithium dissolution, and SEI morphology. It is found that increasing salt concentration in a LiFSI/DMC electrolyte from 1 to 5 and then to 10 M yields significant changes in SEI morphology. The 1 M electrolyte led to DMC degradation into -O-CH3 with no significant LiO formation. In contrast, the 5 and 10 M formulations evolved into an SEI structure dominated by continuous and stratified LiO and LiF phases.Changes in the SEI morphology based on the E/A ratio for the 10 M LiFSI/DMC electrolyte revealed the existence of an intermediate E/A ratio leading to a more compact and more inorganic-rich SEI; the formed LiO phase density was higher than that in other ensembles representative of dry and flooded electrolyte operation conditions. Our third set of calculations focused on the effect of solvent chemistry. The 5 M LiFSI/DME electrolyte led to the formation of a LiO phase surrounded by some residual DME solvent; in this wetted SEI, the residual solvent provides diffusion channels for Li+ ions. Finally, we tested the impact of adding 1,1,2,2-tetrafluoroethylene 2,2,3,3-tetrafluoropropyl ether (TTE) as a diluent into the electrolyte using a 1.3 M LIFSI:DMC:TTE (1:1.2:3 molar ratio) formulation. The TTE diluent showed decomposition and helped grow a LiF-dominated SEI film with a lower LiO/LiF phase ratio than the equivalent 5.0 M LiFSI/DMC formulation with no electrolyte. These results form the basis for a deeper understanding of the SEI formation mechanisms and provide a design guideline for SEI films based on the lithium salt concentration, relative electrolyte/electrode content, and presence of a diluent.

Terahertz spectral vibrational properties and weak interactions analysis of caffeic acid and ferulic acid

Caffeic acid and its derivative, ferulic acid, are a class of natural phenolic compounds with strong antioxidant properties and have good application prospects in the field of medicine. In this paper, the spectral characteristics and the types of intermolecular interactions of caffeic acid and ferulic acid were analyzed using terahertz (THz) detection method combined with quantum chemical correlation analysis methods. The absorption spectra of caffeic acid and ferulic acid in the 0.4–2.0 THz band were measured by terahertz time-domain spectroscopy (THz-TDS) detection system. The theoretical spectra of caffeic acid and ferulic acid in this band were simulated by structure optimization and frequency calculation with the help of density functional theory (DFT), and the theoretical and experimental spectra were in good agreement. To resolve the spectral information in detail, we used the Potential Energy Distribution (PED) method to assign the vibrational modes of the absorption peaks, then identified the types of intermolecular interactions by interaction region indicator (IRI) and energy decomposition analysis based on forcefield (EDA-FF) methods to explain the reasons for the formation of vibrations. The results show that the main vibrational modes of caffeic acid in the absorption peak are dihedral torsion, for ferulic acid are bond angle bending and dihedral torsion. Intermolecular interactions play an important role in these vibrations, with van der Waals effects predominant, while the intermolecular hydrogen bonding model overall vibrates. This work demonstrates that using THz spectroscopy combined with DFT, IRI, and EDA-FF methods, can analyze the weak interaction types of structurally similar substances efficiently.

Qualitative and quantitative study of intermolecular weak interactions for aminosalicylic acid isomers by terahertz spectroscopy

AbstractIn the field of chemical science, the development of new drugs, the formation of crystals and molecular clusters, and the optimization of drug safety and efficacy are all closely related to weak molecular interactions. In this paper, the salicylic drugs 4‐aminosalicylic acid (4‐ASA) and 5‐aminosalicylic acid (5‐ASA) are used as the research objects. First, the terahertz (THz) absorption spectra of the two isomers were measured in the range of .4–2.0 THz by terahertz time‐domain spectroscopy (THz‐TDS). Then the unit cells were calculated by using density functional theory (DFT). We found that the characteristic absorption peaks of the experimental spectra were basically consistent with the theoretical calculation. In addition, under the solvent model, the free energy of dissolution and the free energy of the systems were considered and calculated, and the results showed that solvation had a certain influence on the position and intensity of spectral absorption peaks. In order to further explore the origin of the characteristic absorption peaks, the vibrational properties of the unit cell model were analyzed using the potential energy distribution (PED) method. At the same time, the weak interactions of the system were qualitatively and quantitatively analyzed by interaction region indicator (IRI) and energy decomposition analysis based on forcefield (EDA‐FF) methods, respectively. The results show that the absorption peaks of 4‐ASA and 5‐ASA are mainly derived from the vibration mode of dihedral angle torsion. The weak interactions in the 4‐ASA are dominated by dispersion, while they are dominated by electrostatic and dispersion in the 5‐ASA. Therefore, it is an effective way to identify isomers and study intermolecular weak interactions by using THz‐TDS combined with PED, IRI, and EDA‐FF.

Conformational Energy Benchmark for Longer n-Alkane Chains.

We present the first benchmark set focusing on the conformational energies of highly flexible, long n-alkane chains, termed ACONFL. Unbranched alkanes are ubiquitous building blocks in nature, so the goal is to be able to calculate their properties most accurately to improve the modeling of, e.g., complex (biological) systems. Very accurate DLPNO-CCSD(T1)/CBS reference values are provided, which allow for a statistical meaningful evaluation of even the best available density functional methods. The performance of established and modern (dispersion corrected) density functionals is comprehensively assessed. The recently introduced r2SCAN-V functional shows excellent performance, similar to efficient composite DFT methods like B97-3c and r2SCAN-3c, which provide an even better cost-accuracy ratio, while almost reaching the accuracy of much more computationally demanding hybrid or double hybrid functionals with large QZ AO basis sets. In addition, we investigated the performance of common wave function methods, where MP2/CBS surprisingly performs worse compared to the simple D4 dispersion corrected Hartree-Fock. Furthermore, we investigate the performance of several semiempirical and force field methods, which are commonly used for the generation of conformational ensembles in multilevel workflows or in large scale molecular dynamics studies. Outstanding performance is obtained by the recently introduced general force field, GFN-FF, while other commonly applied methods like the universal force field yield large errors. We recommend the ACONFL as a helpful benchmark set for parametrization of new semiempirical or force field methods and machine learning potentials as well as a meaningful validation set for newly developed DFT or dispersion methods.

Nearest-Neighbor dsDNA Stability Analysis Using Alchemical Free-Energy Simulations.

The thermodynamic stability of double-stranded (ds)DNA depends on its sequence. It is influenced by the base pairing and stacking with neighboring bases along DNA molecules. Semiempirical schemes are available that allow us to predict the thermodynamic stability of DNA sequences based on empirically derived nearest-neighbor contributions of base pairs formed in the context of all possible nearest-neighbor base pairs. Current molecular dynamics (MD) simulations allow one to simulate the dynamics of DNA molecules in good agreement with experimentally obtained structures and available data on conformational flexibility. However, the suitability of current force field methods to reproduce dsDNA stability and its sequence dependence has been much less well tested. We have employed alchemical free-energy simulations of whole base pair transversions in dsDNA and in unbound single-stranded partner molecules. Such transversions change the sequence context but not the nucleotide content or base pairing in dsDNA and allow a direct comparison with the empirical nearest-neighbor dsDNA stability model. For the alchemical free-energy changes in the unbound single-stranded (ss)DNA partner molecules, we tested different setups assuming either complete unstacking or unrestrained simulations with partial stacking in the unbound ssDNA. The free-energy simulations predicted nearest-neighbor effects of similar magnitude, as observed experimentally but showed overall limited correlation with experimental data. An inaccurate description of stacking interactions and other possible reasons such as the neglect of electronic polarization effects are discussed. The results indicate the need to improve the realistic description of stacking interactions in current molecular mechanic force fields.

On (non-)conservative body forces, vorticity generation and energy conversion in ideal flows

Usually, the load on lifting bodies in incompressible, inviscid flow is determined by integration of the pressure on the body surface, once the flow is solved. Prandtl (Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch- Physikalische Klasse, vol. 1918, pp. 451–477) proposed an opposite method in which the body force field is the source term in the equation of motion to solve the flow. This force field method has not been used intensively but has regained importance in modern wind energy research. However, an analysis of which type of body force field generates vorticity and converts energy, and which body force field does not, is lacking. Prandtl's method is adopted here, but with the addition that the force field is allowed to be conservative or non-conservative. The relation between conservative/non-conservative body forces, vorticity generation, potential and kinetic energy and Helmholtz's vorticity theorems are derived. Similarly, the load on lifting bodies in two and three dimensions is classified as (non-)conservative, with some examples. To show that the force field method is consistent with the method where the load is output of an analysis, the expression for the Kutta–Joukowsky load and the relation between bound and trailing vorticity of a wing have been rederived using the force field method. The analysis confirms that this relation between bound and trailing vorticity is not governed by Helmholtz's theorems, as is often assumed, but by the non-conservative force field generating vorticity.

Automated Molecular Cluster Growing for Explicit Solvation by Efficient Force Field and Tight Binding Methods.

An automated and broadly applicable workflow for the description of solvation effects in an explicit manner is introduced. This method, termed quantum cluster growth (QCG), is based on the semiempirical GFN2-xTB/GFN-FF methods, enabling efficient geometry optimizations and MD simulations. Fast structure generation is provided using the intermolecular force field xTB-IFF. Additionally, the approach uses an efficient implicit solvation model for the electrostatic embedding of the growing clusters. The novel QCG procedure presents a robust cluster generation tool for subsequent application of higher-level (e.g., DFT) methods to study solvation effects on molecular geometries explicitly or to average spectroscopic properties over cluster ensembles. Furthermore, the computation of the solvation free energy with a supermolecular approach can be carried out with QCG. The underlying growing process is physically motivated by computing the leading-order solute-solvent interactions first and can account for conformational and chemical changes due to solvation for low-energy barrier processes. The conformational space is explored with the NCI-MTD algorithm as implemented in the CREST program, using a combination of metadynamics and MD simulations. QCG with GFN2-xTB yields realistic solution geometries and reasonable solvation free energies for various systems without introducing many empirical parameters. Computed IR spectra of some solutes with QCG show a better match to the experimental data compared to well-established implicit solvation models.

Computer Generated Realistic Interstellar Icy Grain Models: Physicochemical Properties and Interaction with NH3.

Interstellar grains are composed by a rocky core (usually amorphous silicates) covered by an icy mantle, the most abundant molecule being H2O followed by CO, CO2, NH3, and also radicals in minor quantities. In dense molecular clouds, gas-phase chemical species freeze onto the grain surface, making it an important reservoir of molecular diversity/complexity whose evolution leads to interstellar complex organic molecules (iCOMs). Many different models of water clusters have appeared in the literature, but without a systematic study on the properties of the grain (such as the H-bonds features, the oxygen radial distribution function, the dangling species present on the mantle surface, the surface electrostatic potential, etc.). In this work, we present a computer procedure (ACO-FROST) grounded on the newly developed semiempirical GFN2 tight-binding quantum mechanical method and the GFN-FF force field method to build-up structures of amorphous ice of large size. These methods show a very favorable accuracy/cost ratio as they are ideally designed to take noncovalent interactions into account. ACO-FROST program can be tuned to build grains of different composition mimicking dirty icy grains. These icy grain models allow studying the adsorption features (structure, binding energy, vibrational frequencies, etc.) of relevant species on a large variety of adsorption sites so to obtain a statistically meaningful distribution of the physicochemical properties of interest to be transferred in numerical models. As a test case, we computed the binding energy of ammonia adsorbed at the different sites of the icy grain surface, showing a broad distribution not easily accounted for by other more size limited icy grain models. Our method is also the base for further refinements, adopting the present grain in a more rigorous QM:MM treatment, capable of giving binding energies within the chemical accuracy.

Towards electronic structure-based ab-initio molecular dynamics simulations with hundreds of millions of atoms

We push the boundaries of electronic structure-based ab-initio molecular dynamics (AIMD) beyond 100 million atoms. This scale is otherwise barely reachable with classical force-field methods or novel neural network and machine learning potentials. We achieve this breakthrough by combining innovations in linear-scaling AIMD, efficient and approximate sparse linear algebra, low and mixed-precision floating-point computation on GPUs, and a compensation scheme for the errors introduced by numerical approximations. The core of our work is the non-orthogonalized local submatrix method (NOLSM), which scales very favorably to massively parallel computing systems and translates large sparse matrix operations into highly parallel, dense matrix operations that are ideally suited to hardware accelerators. We demonstrate that the NOLSM method, which is at the center point of each AIMD step, is able to achieve a sustained performance of 324 PFLOP/s in mixed FP16/FP32 precision corresponding to an efficiency of 67.7% when running on 1536 NVIDIA A100 GPUs.

Benchmark Study on the Calculation of 119Sn NMR Chemical Shifts.

A new benchmark set termed SnS51 for assessing quantum chemical methods for the computation of 119Sn NMR chemical shifts is presented. It covers 51 unique 119Sn NMR chemical shifts for a selection of 50 tin compounds with diverse bonding motifs and ligands. The experimental reference data are in the spectral range of ±2500 ppm measured in seven different solvents. Fifteen common density functional approximations, two scalar- and one spin-orbit relativistic approach are assessed based on conformer ensembles generated using the CREST/CENSO scheme and state-of-the-art semiempirical (GFN2-xTB), force field (GFN-FF), and composite DFT methods (r2SCAN-3c). Based on the results of this study, the spin-orbit relativistic method combinations of SO-ZORA with PBE0 or revPBE functionals are generally recommended. Both yield mean absolute deviations from experimental data below 100 ppm and excellent linear regression determination coefficients of ≤0.99. If spin-orbit calculations are not affordable, the use of SR-ZORA with B3LYP or X2C with ωB97X or M06 may be considered to obtain qualitative predictions if no severe spin-orbit effects, for example, due to heavy nuclei containing ligands, are expected. An empirical linear scaling correction is demonstrated to be applicable for further improvement, and respective empirical parameters are given. Conformational effects on chemical shifts are studied in detail but are mostly found to be small. However, in specific cases when the ligand sphere differs substantially between conformers, chemical shifts can change by up to several hundred ppm.

Formation of Linear Oligomers in Solid Electrolyte Interphase via Two‐Electron Reduction of Ethylene Carbonate

AbstractSolid electrolyte interphase (SEI) plays a significant role in enhancing the stability and durability of lithium metal batteries (LMBs) by separating highly reactive lithium metal anode (LMA) from the electrolyte to avoid continuous degradation. However, the underlying reaction mechanism is still far from clear. Herein, a hybrid ab initio and reactive force field (HAIR) method is employed to extend the ab initio molecular dynamics (AIMD) to 1 ns, which provides crystal information about the reaction mechanism of elementary reactions that can explain the components and morphology evolution of SEI formation. Specifically, HAIR simulation confirms the two‐electron (2e–) reduction of ethylene carbonate (EC) by releasing CO and CO2, agreeing with phenomenal experiment observation. As the unsaturated intermediates accumulate, polymerization reactions occur, producing linear polyethylene oxide (PEO), Li2OCO2CH2CH2, Li2OCO2(CH2)4, etc., which regulate the formation of outer organic layer (OOL) that consists of linear polyethylene oxide (PEO), Li2OCO2CH2CH2, Li2OCO2(CH2)4, etc., and the inner inorganic layer (IIL) mainly consists of LiF and Li2O. Simulations at low concentration (LC, 1M) and high concentration (HC, 5M) reveal significantly different reaction pathways when HC electrolyte can significantly promote the formation of homogenous LiF that has been regarded as an important component to facilitate robust SEI.

Modeling the Structure and Interactions of Intrinsically Disordered Peptides with Multiple Replica, Metadynamics-Based Sampling Methods and Force-Field Combinations.

Intrinsically disordered proteins play a key role in many biological processes, including the formation of biomolecular condensates within cells. A detailed characterization of their configurational ensemble and structure–function paradigm is crucial for understanding their biological activity and for exploiting them as building blocks in material sciences. In this work, we incorporate bias-exchange metadynamics and parallel-tempering well-tempered metadynamics with CHARMM36m and CHARMM22* to explore the structural and thermodynamic characteristics of a short archetypal disordered sequence derived from a DEAD-box protein. The conformational landscapes emerging from our simulations are largely congruent across methods and force fields. Nevertheless, differences in fine details emerge from varying combinations of force-fields and sampling methods. For this protein, our analysis identifies features that help to explain the low propensity of this sequence to undergo self-association in vitro, which are common to all force-field/sampling method combinations. Overall, our work demonstrates the importance of using multiple force-field and sampling method combinations for accurate structural and thermodynamic information in the study of disordered proteins.

Crystal shapes, triglyphs, and twins in minerals: The case of pyrite

Abstract The euhedral shapes of pyrite FeS2 are usually exposing three main surfaces: striated (001), smooth (111), and striated (210), leading to the cubical, octahedral, and pyritohedral morphology, respectively. The macroscopic striations, sometimes called triglyphs on cubic crystals, are parallel on specific surfaces and aligned to the <100> directions. Other types of striated and unstriated (hkl) surfaces can be observed on pyrite crystals from Peru, a country offering a rich diversity of pyrite shapes. A rare specimen from Elba Island (Italy) is a pyritohedron with uncommon directions of striations (so-called “negative” striations, first described in Japanese minerals). The Wulff kinetic growth and the periodic bond chain (PBC) theories were not relevant enough to explain crystal shapes, the texture of the surfaces, and twinning. To bring some new insights on crystal growth, twinning, and anisotropy, pyrite samples are analyzed using XRD, SEM, and EDS techniques coupled with atomistic simulations. A first analysis points out that sulfur terminations play a key role in the growth of striations in distinguishing the six <001> directions. The negative striated pyritohedral pyrite would be, in fact, a special case that has stabilized the {120} surfaces, which are structurally different from the {210} facets. The {120} surface has a slightly higher surface energy than the {210} surface (surface energies of 1.68 and 1.65 J/m2, respectively, calculated with force field methods). {120} pyritohedra from Elba, Italy, are growing next to micaceous iron oxides (a type of hematite), which are also peculiar specimens with magnetic properties. Another specificity is that some rare earth elements have been identified in the pyrite sample from Elba, which leads to a hypothesis that geothermal conditions favor “negative” striations (e.g., discernible in Akita prefecture-Japan, Boyacá-Colombia, and Cassandra-Greece). The striation directions become useful to distinguish (hkl) surfaces and to identify twinning as they follow the same patterns on each interpenetrated crystal. The most common twinning is the “iron cross,” a penetration twin of two crystals defined by a rotation of 90° along an [001] axis with a coincidence in the iron sub-lattice (e.g., twinning by merohedry) and with a twin center. The sulfur network also plays a fundamental role in stabilizing the (001) interface and in keeping the chemical bulk properties at the boundary, as confirmed by additional ab initio simulations. The grain boundary is a 2D defect in which the (001) twinning is relatively stable as it is common. The calculated formation energy of the rotation twinning is 0.8 J/m2. The rotation twinning is associated with an apparent reflection on (110) planes. The formation energy of the (110) mirror grain boundary is 1.7 J/m2, and the interface at the atomic scale is relatively uniform in agreement with experimental observations.

16OSTM10: a new open-shell transition metal conformational energy database to challenge contemporary semiempirical and force field methods.

A new database, 16OSTM10, containing 10 conformations for each of 16 non-multireference realistic-size open-shell transition metal (OSTM) complexes has been developed. Contemporary composite density functional theory (DFT) (PBEh-3c and B97-3c), semiempirical (PM6 and PM7) and the GFNn-xTB/FF family methods were examined against conventional DFT (PBE-D3(BJ), PBE0-D3(BJ), M06 and ωB97X-V) to reproduce the conformational energies. While good performance is observed for the conventional (the average Pearson correlation coefficient is ρ = 0.91) and composite DFT (average ρ = 0.93), semiempirical and force-field methods should still be used with caution for these challenging compounds. The corresponding average ρ values are 0.53 (PM6 and PM7), 0.75 (GFN1-xTB and GFN2-xTB) and 0.62 (GFN-FF). Accounting for the intramolecular dispersion interactions turned out to be crucial for 4 OSTM complexes bearing bulky substituents in close proximity to each other. The influence of the scalar relativistic effects on the conformational energies is negligible for the considered 3d metal species.

Reduction Mechanism of Solid Electrolyte Interphase Formation on Lithium Metal Anode: Fluorine-Rich Electrolyte

Metallic lithium is considered a promising anode that can significantly increase the energy density of rechargeable lithium-based batteries, but problems like uncontrollable growth of lithium dendrites and formation of dead lithium impede its application. Recently, a low-concentration single-salt two-solvent electrolyte, 1 M LiTFSI/FDMA/FEC, has attracted attention because a high coulombic efficiency can be achieved even after many cycles owing to the formation of a robust solid electrolyte interface (SEI). However, the reaction mechanism and SEI structure remain unclear, posing significant challenges for further improvement. Here, a hybrid ab initio and reactive force field (HAIR) method revealed the underlying reaction mechanisms and detailed formation pathway. 1 ns HAIR simulation provides critical information on the initial reduction mechanism of solvent (FDMA and FEC) and salt (LiTFSI). FDMA and FEC quickly decompose to provide F- that builds LiF as the major component of the inner layer of inorganic SEI, which has been demonstrated to protect Li anode. Decomposition of FDMA also leads to a significant nitrogen-containing composition, producing Li-N-C, LixN, and other organic components that increase the conductivity of SEI to increase performance. XPS analysis confirms evolution of SEI morphology consistent with available experiments. These results provide atomic insight into SEI formation, which should be beneficial for the rational design of advanced electrolytes.

ReaxFF Force Field Development and Application for Toluene Adsorption on MnMOx (M = Cu, Fe, Ni) Catalysts.

In numerous studies, the application of the molecular dynamics scheme based on the reactive force field (ReaxFF) method has been proven effective in modeling the catalytic behavior of metal–organic compounds. Recently, this method has been successfully applied for MxOy (M = Cu, Fe, Mn, Ni) transition-metal oxides. Yet, bimetallic metal oxides of the type MnMOx (M = Cu, Fe, Ni) were also present in the experimental system but could not be modeled since not all of the force field parameters were available at the time. To bridge this gap, the force field for modeling bimetallic metal oxides had to be developed. Here, we establish the needed force field parameter sets (namely, Cu/Mn/O, Fe/Mn/O, and Ni/Mn/O) and apply them to the problem of toluene adsorption on bimetallic oxide catalyst surfaces to verify their validity. Each training set consisted of at least 10 crystal structures containing at least Cu–Mn–O, Fe–Mn–O, or Ni–Mn–O atoms in contact obtained from the available structure databases. The parameter training has been done using the in-home-compiled version of the ReaxFF code. After training the force fields for geometry reproduction, the parameters were refined using the optimization by atom charges, comparing the ReaxFF values to those obtained for the respective structures using periodic crystal density functional theory (DFT) codes. The as-developed force fields were then applied to the process of toluene adsorption/degradation on MnMOx catalysts. Results obtained show agreement with previous experimental expectations, although some remarks are given since the initially presumed crystal structure of bimetallic oxide Mn1–xMxOy crystallites may still have an impact on theoretical predictions. The presented are, to the best of the authors’ knowledge, the first applications of the ReaxFF approach to the Mn–(Cu|Fe|Ni)–O–C–H interaction.

Strontium stannate as an alternative anode for Na- and K-Ion batteries: A theoretical study

Theoretical predictions on structural, electronic and transport properties of pristine and alkali-doped strontium stannate (SrSnO3) were made using density functional theory and force field methods. Results of electronic structure computations show that a doping of alkali-ion (Li+, Na+ and K+) into SrSnO3 induces the apparition of extra energy bands on the valence and conduction bands and small translation of the valence and conduction band limits. This is more accentuated in K+-ion doped samples with lower energy gap. Defect energetics computations reveal a low energetic cost associated the alkali incorporation mechanism proposed in this work. Such a mechanism provides us with an intermediate first discharge reaction to describe the delithiation process. Results on alkali ion transport properties in interstitially doped nanocrystalline SrSnO3 samples reveal lower diffusion activation energies of 0.25, 0.28 and 0.44 eV and diffusion coefficient at 25 °C of 9.6, 2.9 × 10−11 and 4.8 × 10−13 cm2s−1 for Li-, Na- and K-doped samples, respectively. These predicted properties bring in new evidence to stimulate a consideration of strontium stannate for use as an alternative anode, in particular for both Na- and K-ion batteries.

Obstacle avoidance for orchard vehicle trinocular vision system based on coupling of geometric constraint and virtual force field method

Nowadays the use of visual navigation in orchard is rapidly growing, while current research mainly focuses on orchard row detection or obstacle detection separately. The economic, fast and reliable navigation vision system that completing orchard row following and obstacle avoidance simultaneously and the obstacle avoidance algorithm for vision system without complex multiple navigation systems combining are needed further research. In this paper, a trinocular vision system for orchard vehicle is set up and the obstacle avoidance algorithm based on coupling of geometric constraint and virtual force field is designed for its vision system.First of all, based on analyzing the different vision system characteristics and the detection demand of orchard obstacle avoidance the trinocular vision system for orchard vehicle is set up based on a wide-angle camera and binocular stereo vision system. Then, the image processing algorithm of orchard row and obstacle detection is designed. For orchard row detection, the trunk regions enhancement algorithm is designed based on grayscale morphology filtering the trunk regions prediction algorithm is designed based on optical flow method to improve the trunk regions detection speed and accuracy. For obstacle detection, the background equalization algorithm based on H-channel image characteristics and the interference weaken algorithm with G-channel image characteristics are designed. Based on the row and obstacle detection results the algorithm for obstacle avoidance in orchard based on coupling of geometric constraint and virtual force field is designed. In the obstacle avoidance process, the virtual force field method is used as the mainly control of the vehicle obstacle avoidance process, and the geometric constraint between visual model of trinocular vision system and obstacle position is coupling with it to fulfill the avoidance demand of the obstacle with special shape and other condition that influence the virtual force field calculation.The experimental results show that the trinocular vision system for orchard vehicle built in this paper has strong adaptability to the actual environment which is accurate and stable for orchard row detection and obstacle detection simultaneously. The average deviation is 4.76 cm and 7.05 cm at 0.5 m/s and 1.0 m/s respectively, the average deviation of obstacle distance detection in the Z-axis direction is 3.18 cm, and in the X-axis direction is 0.45 cm. And the obstacle avoidance algorithm designed in this paper is effective in the orchard which can meet the actual production requirements. The research results will lay a foundation for the development of intelligent equipment and unmanned management in orchard.