Electrostatic Energy Research Articles

SO3NH3 crystal growth in (CH3)3SBr solution

SO3NH3 (Sulfamic acid, or SA) is known for its excellent piezoelectric and optical properties, making it valuable for various optical applications. However, it usually takes weeks to months to grow the SA single crystals with centimeter-scale size by traditional growth method from solution. In this study, we use (CH3)3SBr (Me3SBr) as an additive to enhance the growth rate of SA single crystals, and the growth time was reduced to just 48 h. The mechanism of accelerated crystallization process is attributed to the variations of electrostatic potential and binding energy on SA crystal modified by the additive. In addition, structural analysis and basic characterization on the newly grown SA are performed, and first-principles calculations provide insights into the energy band structure and phonon spectrum.

Cellulose acetate-based polymer electrolyte for energy storage application with the influence of BaTiO3 nanofillers on the electrochemical properties: A progression in biopolymer-EDLC technology

The bio-based solid polymer electrolyte serves as a promising choice for the next generation of energy storage devices to meet the requirement of green chemistry. In the current research, a green plasticized magnesium ion-conducting biopolymer electrolyte was developed using simple solution casting method for Electric Double Layer Capacitors (EDLC) applications. The biopolymer Cellulose Acetate (CA) as the host polymer, with varying concentrations of BaTiO3 as the nanofiller, Mg(CF3SO3)2 as the ionic dopant, and PEG as the plasticizer. A 2 wt% addition of BaTiO3 to the biopolymer electrolyte exhibits maximum conductivity measuring 2.4 × 10−3 S/cm. Linear Sweep Voltammetry (LSV) analysis demonstrates maximum stability voltage of 3.51 V. The ionic transference number (tion) and (tMg2+) were determined to be 0.99 and 0.41 respectively. The fabricated EDLC device with the same electrolyte showed polarisation curve without any noticeable peaks in the Cyclic Voltammetry (CV) plot, indicating no redox reactions occurring at the electrode-electrolyte interface. Galvanostatic Charge Discharge (GCD) results showed excellent coulombic efficiency, stability and Energy Density and Power Density performance over 2000 cycles. The incorporation of BaTiO3 into biopolymer membranes presents a viable approach towards sustainable energy storage solutions by enhancing the energy storage capacity of EDLC devices.

Enlarged Curvature, Torsion and Torque in Helical Conformations and the Stability and Growth of α-Peptide under the Isochoric and Isobaric Conditions: Variatonal Optimization

The torsional deformation behavior of an elastic bar with a circular cross-section was investigated by applying invariant dyadic analysis, where the small finite displacement functions advocated by Saint-Venant (1855) were fully employed. It was found that the previously overlooked circumferential shear force field generated by pure torsion on the side walls of a bar produces an unusual torque term induced by the skew-symmetric part of the deformation tensor and exhibits quadratic length dependence along the z-axis of the bar. The adaptation of this torque term for a helical conformation of α-peptides creates moments acting on the circular cross-sections and is directed along the surface normal of circular cross-sections, which coincides with the tangent vector of the helix. The projection of this torque along the z-axis of the helix varies quadratically with the azimuthal angle. The radial component of the unusual torque, which also lies along the principal normal vector of the helix, starts to perform a precession motion by tracking a spiral orbit around the z-axis, whereas its apex angle decreases asymptotically with the azimuthal angle and finally reaches a finite value depending on the height of the helix along the z-axis. The ordinary torque terms, which are also deduced from the self- and anti-self-conjugate parts of the deformation tensor, have magnitudes half that of the full torque term reported in the literature. The present results were applied to the helical conformation of α-peptides designated by {3.611} to show that the mechanical stability of strained open-ended helical conformations can be successfully achieved by spontaneous readjustments of the surface and bulk Helmholtz free energies under isothermal isochoric conditions. It has been demonstrated that the main contribution to the mechanical stability of α-peptide 3.611 cannot come alone from the electrostatic dipole-dipole interaction potential of the anti-align excess dipole pairs but also from the surface Helmholtz free energy, which is characterized by a binding free energy of -15.5 eV/molecule (-32.56 Kcal/mole) for an alpha-peptide composed of 11 amino acid residues with a critical arc length of approximately 10 nm, assuming that the shear modulus is G = 1GPa and the surface Helmholtz specific free energy density is fs = 800 erg/cm2. This result was in excellent agreement with the experimental observations of the AH-1 conformation of (Glu)n Cys at pH 8. The present theory indicates that only two excess permanent anti-align dipole pairs for one α-Helical peptide molecule is requirement to stabilize the whole secondary structure of the protein that is exposed to heavy torsional deformation during the folding processes which amounts to 7.75 eV/molecule stored electrostatic energy compared to the interfacial Helmholtz free energy of -23.25 eV/molecule, which is exposed to hydrophobic environments.

Electrical conduction and optical characteristics of Li2O and Bi2O3 Co-doped zinc-phosphate glassy nanocomposites: A critical observation of mixed ionic electronic effect

In the present report, the combined effects of the co-doping of metal oxide (Bi2O3) and Lithium oxide (Li2O) into the glassy matrix with chemical composition xLi2O-(0.45-x)Bi2O3-(0.15ZnO-0.40P2O5) (x = 0.05, 0.15, 025, and 0.35 mol%) are investigated thoroughly. The FESEM and X-ray diffraction data affirm the crystalline nature of the studied glassy composites. The obtained band gap energy values are declined from (3.68–3.17) eV, while the Urbach energy values are declined from (0.38–0.27) eV. Moreover, the mechanism responsible for AC conductivity has been analyzed using Almond–West formalism and Jonscher's universal power law. The observed rise in both AC and DC conductivity in the glass samples is attributed to the mixed ionic electronic effect. In the ionic diffusion model, an increased defect site concentration improves Li+ ion migration through percolation channels. The reduction in both electrostatic binding energy and strain energy lowers the Anderson-Stuart activation energy, facilitating Li+ ion migration and enhancing conductivity. Additionally, in the small polaron hopping model, an increase in the density of defect states suggests more defect sites that facilitate electronic hopping, creating deep localized states and transitions between localized and extended states. Replacing a Bismuth atom with a Lithium atom increases the number of non-bridging oxygen, enhancing the conduction band tail, reducing the energy needed for hopping conductivity, and increasing conductivity.

Crystal structure and Hirshfeld surface analyses, crystal voids, intermolecular interaction energies and energy frameworks of 3-benzyl-1-(3-bromopropyl)-5,5-diphenylimidazolidine-2,4-dione

The title molecule, C25H23BrN2O2, adopts a cup shaped conformation with the distinctly ruffled imidazolidine ring as the base. In the crystal, weak C—H...O hydrogen bonds and C—H...π(ring) interactions form helical chains of molecules extending along the b-axis direction that are linked by additional weak C—H...π(ring) interactions across inversion centres. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (51.0%), C...H/H...C (21.3%), Br...H/H...Br (12.8%) and O...H/H...O (12.4%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 251.24 Å3 and 11.71%, respectively, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated by the dispersion energy.

Anisole-Water and Anisole-Ammonia Complexes in Ground and Excited (S1) States: A Multiconfigurational Symmetry-Adapted Perturbation Theory (SAPT) Study.

Binary complexes of anisole have long been considered paradigm systems for studying microsolvation in both the ground and electronically excited states. We report a symmetry-adapted perturbation theory (SAPT) analysis of intermolecular interactions in anisole-water and anisole-ammonia complexes within the framework of the multireference SAPT(CAS) method. Upon the S1 ← S0 electronic transition, the hydrogen bond in the anisole-water dimer is weakened, which SAPT(CAS) shows to be determined by changes in the electrostatic energy. As a result, the water complex becomes less stable in the relaxed S1 state despite decreased Pauli repulsion. Stronger binding of the anisole-ammonia complex following electronic excitation is more nuanced and results from counteracting shifts in the repulsive (exchange) and attractive (electrostatic, induction and dispersion) forces. In particular, we show that the formation of additional binding N-H···π contacts in the relaxed S1 geometry is possible due to reduced Pauli repulsion in the excited state. The SAPT(CAS) interaction energies have been validated against the coupled cluster (CC) results and experimentally determined shifts of the S1 ← S0 anisole band. While for the hydrogen-bonded anisole-water dimer SAPT(CAS) and CC shifts are in excellent agreement, for ammonia SAPT(CAS) is only qualitatively correct.

Rational design, synthesis, computational studies and biological evaluation of new diazepanone derivatives: Crystal structure of 2,7-bis(4-chlorophenyl)-1,3-dimethyl-1,4-diazepan-5-one

Structural and biological evaluation of newly designed and synthesized diazepanone derivatives (3a-c) with modified functionalities is reported in this paper, as liponucleoside class of antibiotics possessing 1,4-diazepanone as core moiety are under investigation since last decade to improvise their drug action. FT-IR, HR-ESI-MS, 1H NMR and 13C NMR spectral studies are used for the structural characterization of synthesized compounds (3a-c). 1H NMR spectral data reveal that the diazepanone ring exhibits chair conformation in solution state. The solid state geometry for compound 3a acquired by SC-XRD study also in favour of chair conformation of the diazepanone ring with equatorial orientation of all the substituents. Comparison of experimental bond parameters with theoretical results attained by DFT studies using B3LYP/6–311G++ (d,p) basis set are in good agreement. Molecular electrostatic potential surface (MEPS) and HOMO-LUMO energies are used to elucidate the topology and physicochemical parameters of 3a. Nature of crystal packing is ascertained by Hirshfeld surface and its delineated 2D-Fingerprint plot in addition with the SC-XRD evidences. Antibacterial evaluation of (3a-c) against tested bacterial strains reveals that the compounds have remarkable antibacterial potencies compared to tested standard drug. Among the compounds 3a-c, the compound 3c with fluoro-substitution on the phenyl ring shows highest activity.

An experimental and computational investigation of the cyclopentene-containing peptide-derived compounds: focus on pseudo-cyclic motifs via intramolecular interactions.

Conformational flexibility is one of the main disadvantages of peptide-based compounds. We focus on their molecular 'chameleonicity' related to forming pseudo-cyclic motifs via modulation of weak intramolecular interactions. It is an appealing strategy for controlling equilibrium between the polar open and the nonpolar closed conformations. Within this context, we report here the crystal structure of the (R)-(2-tert-butoxycarbonyl)amino-1-oxo-3-phenyl)propyl)-1-cyclopentene (1), synthesis of which in high yield was achieved by a facile multi-step protocol. Our Cambridge Structural Database (CSD) overview for the peptide-based crystals revealed the exclusivity of this compound from the viewpoint of the unusual pseudo-bicyclic system via C-H…O and C-O…π interactions, in which cyclopentene shields the amide bond. Notably, cyclopentene as a bioisostere of proline is an appealing scaffold in medicinal chemistry. An extensive combined experimental and computational study provided more profound insight into the supramolecular landscape of 1 with respect to similar derivatives deposited in the CSD, including the tendency of cyclopentene for the generation of pseudo-cyclic motifs through weak H-bonding and π-based intramolecular interactions. These weak interactions have been examined by either the quantum theory of 'atoms-in-molecules' (QTAIM) or complex Hirshfeld surface methodology, including enrichment ratios, molecular electrostatic potential surfaces and energy frameworks. In all analysed crystals, all types of H-bonded motifs involving cyclopentene are formed at all levels of supramolecular architecture. A library of cyclopentene-based H-bonding synthons is provided. A molecular docking study depicted vital interactions of cyclopentene with key amino acid residues inside the active sites of two prominent protein kinases, uncovering the therapeutic potential of 1 against breast cancer. To a large extent, dispersion forces have significance in stabilizing the supramolecular structure of both ligand and bio-complex ligand-protein. Finally, the satisfactory in silico bio-pharmacokinetic profile of 1 related to drug-likeness and blood-brain barrier permeation was also revealed.

The adsorption of p-hydroxybenzoic acid on graphene oxide under different pH and in-situ desorption in direct current electric field

The development and ongoing optimization of measures to reduce and eliminate p-hydroxybenzoic acid (p-HBA) in industrial wastewater are significant due to its potential carcinogenic effect and bio-recalcitrant. Graphene oxide (GO) is an ideal adsorbent for removing aromatic acids and achieving adsorbent recovery and resource conservation. In this study, the adsorption properties of p-HBA onto GO at different pH values and the regeneration mechanism of adsorbent under varying electric field intensities were analyzed using molecular dynamics (MD) simulation. The simulation results demonstrate that GO exhibits preferable adsorption capabilities for p-HBA at low pH, and van der Waals (vdW) interaction plays a leading role. However, the adsorption stability decreases at high pH (particularly pH > 9.3) with most p-HBA desorption from the GO surface. When an electric field of 1.0 V/nm is applied to the acidic system (HGO_HBA_HBA−), the total adsorption interaction energy between GO and p-HBA decreases but remains high (−1836.93 kJ/mol). When a 0.6 V/nm electric field is added to the alkaline system (GO2−_HBA2−), the vdW and electrostatic interaction energies are recorded as −35.34 kJ/mol and 3546.97 kJ/mol. The vdW interaction is weak, and electrostatic repulsion increases, facilitating the desorption of p-HBA from the GO surface. This work aims to share insights into the microscopic removal mechanism of p-HBA on the GO surface under different pH values and provide a theoretical perspective on the regeneration mechanism of GO.

High-Density Capacitive Energy Storage in Low-Dielectric-Constant Polymer PMMA/2D Mica Nanofillers Heterostructure Composite

The ubiquitous, rising demand for energy storage devices with ultra-high storage capacity and efficiency has drawn tremendous research interest in developing energy storage devices. Dielectric polymers are one of the most suitable materials used to fabricate electrostatic capacitive energy storage devices with thin-film geometry with high power density. In this work, we studied the dielectric properties, electric polarization, and energy density of PMMA/2D Mica nanocomposite capacitors where stratified 2D nanofillers are interfaced between the multiple layers of PMMA thin films using two heterostructure designs of the capacitors, PMMA/2D Mica/PMMA (PMP) and PMMA/2D Mica/PMMA/2D Mica/PMMA (PMPMP). The incorporation of a 2D Mica nanofiller in the low-dielectric-constant PMMA leads to an enhancement in the dielectric constant, with ∆ε ~ 15% and 53% for PMP and PMPMP heterostructures at room temperature. Additionally, a significant improvement in discharged energy density was measured for the PMPMP capacitor (Ud ~ 38 J/cm3 at 825 MV/m) compared to the pristine PMMA (Ud ~ 9.5 J/cm3 at 522 MV/m) and PMP capacitors (Ud ~ 19 J/cm3 at 740 MV/m). This excellent capacitive and energy storage performance of the PMMA/2D Mica heterostructure nanocomposite may inform the fabrication of thin-film, high-density energy storage capacitor devices for potential applications in various platforms.

Spherical image potentials for an N-charged particle system

The potential energy interaction between a system of N -charged particles and a spherical conducting surface is obtained by means of direct integration of the electrostatic energy density. Making use of the image charge method, we show that the full potential can be split into a sum of one-body central potentials and two-body contributions related to particle–particle and particle–sphere interactions. Analytical expressions are provided for all contributions. The spherical surface of radius R can be considered to correspond to a cavity inside a conductor or a metallic ball, with two different electric conditions, namely the grounded and isolated charged cases. By taking the limit R → ∞ of the spherical case, one recovers the image potential for an N -charged particle system interacting with a planar conductor. While the final results for the potential do not appear as unexpected, the provided analytical expressions should help in diverse physical applications modelled by a number of charged particles interacting close to a spherical surface.

NNN type pincer Pd (II) complexes of pyridine-2,6-dicarboxamides: Catalytic activity and supramolecular formation

Pyridine-2,6-dicarboxamide, NNN pincer type pro-ligands, and their palladium complexes were synthesized. The prepared pro-ligands and complexes were characterized with several characterization techniques (FT-IR, 1H NMR, 13C NMR, and UV-vis analyses). The molecular structure of the acetonitrile-N2,N6-bis(2-bromophenyl)pyridine-2,6-dicarboxamidopalladium(II) complex has been determined by single crystal XRD measurement. This complex contains intramolecular and intermolecular H-bonds, C–H⋅⋅⋅π and face-to-face π⋅⋅⋅π interactions. In addition, two synthons were found in the crystal lattice that have been generated through hydrogen-bond interactions. Homo-synthons (R22(12)), which forms through C–H⋅⋅⋅O intermolecular interactions (2.816 Å for C15–H15⋅⋅⋅O1 and 2.603 Å for C13–H13⋅⋅⋅O2) and hetero-synthons (R21(8)), that generated via C–H⋅⋅⋅N intermolecular interactions (C21–H21C⋅⋅⋅N4, 3.439 Å). Furhermore, homo-synthons (R33(11) and R22(9)) through intermolecular contacts were determined between the palladium complex and the acetonitrile molecules. Furthermore, a quantitative analysis of the noncovalent interactions within the structure was performed using Hirshfeld surface and two-dimensional fingerprint plot analyses. The three-dimensional arrangement of the crystal packing was assessed during the energy-framework calculations, revealing that the electrostatic energy framework had a considerable influence on the dispersion energy framework. The [PdL5] complex provided a conversion of more than 98% and a yield of more than 98% in the shortest time among other catalysts, in which the Suzuki-Miyaura C-C cross-coupling reaction (SMR) was carried out with the 4-bromotoluene substrate. The activity of [PdL5] complex was then examined in the reactions of two other substrates, 1-bromo-4-isobutylbenzene and 2-bromo-6-methoxynaphthalene. Although a yield of over 97% and a conversion of over 97% were observed in the reaction of 1-bromo-4-isobutylbenzene after two hours, the reaction of 2-bromo-6-methoxynaphthalene achieved complete conversion and a yield of over 99% within just one hour.

Modeling and Analysis of MEMS Electrostatic Energy Harvesting System

Modeling and Analysis of MEMS Electrostatic Energy Harvesting System

Crystal structure, Hirshfeld surface analysis, and calculations of inter-molecular inter-action energies and energy frameworks of 1-[(1-hexyl-1H-1,2,3-triazol-4-yl)meth-yl]-3-(1-methyl-ethen-yl)-benzimidazol-2-one.

The benzimidazole moiety in the title mol-ecule, C19H25N5O, is almost planar and oriented nearly perpendicular to the triazole ring. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into a network structure. There are no π-π inter-actions present but two weak C-H⋯π(ring) inter-actions are observed. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (62.0%), H⋯C/C⋯H (16.1%), H⋯N/N⋯H (13.7%) and H⋯O/O⋯H (7.5%) inter-actions. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via the dispersion energy contributions in the title compound.

Flexible PVDF-Ba0.97Ca0.03TiO3 polymer-ceramic composite films for energy storage, biosensor, mechanosensor, and UV–visible light protection

Multifunctional piezoelectric devices, which can detect pressure, store electrostatic energy, block UV radiation, and generate electricity from body movements, are highly beneficial for enhancing individual well-being. To achieve these capabilities, polyvinylidene fluoride (PVDF) composite films with Ba0.97Ca0.03TiO3 (BCT3) filler were prepared, varying the BCT3 content from 0 to 50 wt.%. The BCT3 ceramic, prepared using a modified solid-state reaction, exhibits a tetragonal phase at room temperature with a d33 value of 105 pC/N. X-ray diffraction confirms composite formation. The beta phase ranges from 75 to 86.9 %. At 40 wt.% BCT3, the dielectric constant, energy density, and piezoelectric properties peak, yielding maximum Wrec and Wtot of 138.1 and 284.7 mJ/cm3 (@ 250 kV/cm), respectively. PVDF-BCT3-40 (40 wt.%) shows maximum voltage, current, and power density of 25 V, 26.8 nA, and 19.8 μW/cm3 under a 50 N load. Increasing BCT3 content enhances UV–visible absorbance, making the composites effective for light shielding.

A Study on the Binding Mechanism and the Impact of Key Residue Mutations between SND1 and MTDH Peptide through Molecular Dynamics Simulations.

Metastasis of breast cancer is the main cause of death for patients with breast cancer. The interaction between metadherin (MTDH) and staphylococcal nuclease domain 1 (SND1) plays a pivotal role in promoting breast cancer development. However, the binding details between MTDH and SND1 remain unclear. In this study, we employed all-atom molecular dynamics simulations (MDs) and conducted binding energy calculations to investigate the binding details and the impact of key residue mutations on binding. The mutations in key residues have not significantly affected the overall stability of the structure and the fluctuation of residues near the binding site; they have exerted a substantial impact on the binding of SND1 and MTDH peptide. The electrostatic interactions and van der Waals interactions play an important role in the binding of SND1 and the MTDH peptide. The mutations in the key residues have a significant impact on electrostatic and van der Waals interactions, resulting in weakened binding. The energy contributions of key residues mainly come from the electrostatic energy and van der Waals interactions of the side chain. In addition, the key residues form an intricate and stable network of hydrogen bonds and salt-bridge interactions with the MTDH peptide. The mutations in key residues have directly disrupt the interactions formed between SND1 and MTDH peptide, consequently leading to changes in the binding mode of the MTDH peptide. These analyses unveil the detailed atomic-level interaction mechanism between SND1 and the MTDH peptide, providing a molecular foundation for the development of antibreast cancer drugs.

Remarkable energy storage performance of BiFeO3-based high-entropy lead-free ceramics and multilayers

Electrostatic energy storage capacitors featuring fast charge–discharge capability play an indispensable role in pulsed power capacitors. However, the inverse correlation between polarization and dielectric breakdown strength (Eb) is the main obstacle limiting the access to high recoverable energy storage density (Wrec) and high efficiency (η). In this work, we designed a series of novel (1-x)BiFeO3-x(Ba0.2Sr0.2Ca0.2Bi0.2Na0.2)TiO3 (BF-xBSCBNT, x = 0.4–1.0) high-entropy lead-free relaxor ferroelectric ceramics. The synergy of refined grain size, broadened band gap, and core–shell microstructure is well-investigated by experimental results and phase-field simulations. High polarization difference is achieved by the strengthened relaxation behavior and the dominated polar nanoregions (PNRs). Both high Wrec of 6.0 J/cm3 and η of 81.1 % are achieved in the BF–0.8BSCBNT ceramics. In particular, a remarkable Wrec of 12.1 J/cm3 with a η of 86.1 % are obtained in the multilayer ceramic capacitors (MLCCs) fabricated from the x = 0.8 composition. Excellent temperature stability (<4.0 % in the range of 25–140 °C) and frequency stability (<6.2 % in the range of 1–500 Hz) are also achieved in MLCCs. The excellent energy storage performance demonstrates that high-entropy strategy is effective to develop novel lead-fee ceramics and devices for energy storage applications.

Evaluation of the electrical energy potential of biowaste with methane production kinetics and environmental impact for northeastern region of India

Developing and assessing sustainable energy systems have gained more attention in the circular economy and national growth context as the global energy crisis intends new initiatives. So, this paper aims to evaluate the electrical energy potential of bio-waste from livestock and poultry in the selected area of northeastern India using Waste to Energy (WtE) technology. The environmental impact assessment is also performed with Global Warming Potential (GWP), Acidification Potential (AP), and Dioxin Emission Potential (DEP). The kinetics of methane production are analyzed for two different seasons, summer and winter, by evaluating Bio-Methane Production (BMP). Further, the potential of electric energy and environmental impacts, including kinetics, are assessed. To achieve this, the livestock and poultry population is forecasted using a data-driven model, and the waste profile is estimated. In addition, an optimization algorithm is used to maximize methane production when kinetics are included. The obtained results are compared for cases without and with kinetics in methane production from livestock and poultry manure, and then validated with existing literature. Finally, this study examines the economic feasibility of bio-generation potential to meet the real-time load of the selected site. Accordingly, this work helps in the planning and designing of bioenergy power plants.

Toward Gaussian Process Regression Modeling of a Urea Force Field.

FFLUX is a next-generation, machine-learnt force field built on three cornerstones: quantum chemical topology, Gaussian process regression, and (high-rank) multipolar electrostatics. It is capable of performing molecular dynamics with near-quantum accuracy at a lower computational cost than standard ab initio molecular dynamics. Previous work with FFLUX was concerned with water and formamide. In this study, we go one step further and challenge FFLUX to model urea, a larger and more flexible system. In result, we have trained urea models at the B3LYP/aug-cc-pVTZ level of theory, with a mean absolute error of 0.4 kJ mol-1 and a maximum prediction error below 7.0 kJ mol-1. To test their performance in molecular dynamics simulations, two sets of FFLUX geometry optimizations were carried out: 5 dimers corresponding to energy minima and 75 random dimers. The 5 dimers were recovered with a root-mean-square deviation below 0.1 Å with respect to their ab initio references. Out of the 75 random dimers, 68% converged to the qualitatively same dimer as those obtained at the ab initio level. Furthermore, we have ranked the 5 FFLUX-optimized dimers in the order of their relative FFLUX single-point energies and compared them with the ab initio method. The energy ranking fully agreed but for one crossover between two successive minima. Finally, we have demonstrated the importance of geometry-dependent (i.e., flexible) multipole moments, showing that the lack of multipole moment flexibility can lead to average errors in the total intermolecular electrostatic energy of more than 2 orders of magnitude.

Combined Electrostatic and Strain Engineering of BiFeO3 Thin Films at the Morphotropic Phase Boundary

AbstractMultiferroic BiFeO3 exhibits a morphotropic phase boundary at large compressive strain that merges metastable phases of tetragonal (T) and rhombohedral (R) character resulting in giant ferroelectric and electromechanical responses. To utilize this functionality in devices, it is essential to understand the response of these ferroelectric phases to the environment of a nanoscale heterostructure. Here, the emergence of ferroelectricity near the morphotropic phase boundary in BiFeO3 is explored directly during thin‐film growth, using optical second harmonic generation. It is found that the epitaxial films form at the growth temperature purely in the T phase with zero critical thickness for the spontaneous polarization. Signatures of monoclinic T‐like and R‐like phases only appear upon sample cooling. The robustness of a single‐domain configuration in the high‐temperature T phase is furthermore demonstrated during growth of capacitor‐like metal | ferroelectric | metal heterostructures. Here, a reduction in tetragonality, rather than multidomain formation, lowers the electrostatic energy in the few‐unit‐cell thickness regime. For this lower tetragonality, density‐functional calculations and scanning transmission electron microscopy point to the stabilization of a novel metastable monoclinic structure upon cooling toward room temperature. The synergistic combination of strain and electrostatic phase stabilization in BiFeO3 heterostructures hence provides a basis for designing new ferroelectric phases and ultrathin ferroelectric devices.