Density Functional Calculations Research Articles

An innovative strategy to enhance the interfacial interaction and effective contribution of BN in thermal conductivity in aramid based composites films

With the escalating concern over electronic device overheating, BN/polymer based thermal conductive composites have experienced remarkable growth in the field of heat dissipation. However, it is challenging to enhance the thermal conductivity of composites while preserving strong interfacial interaction due to the dilemma of chemical inertness of BN, interfacial thermal resistance and filler-polymer interaction. Herein, we utilized the adjustable surface charge of polydopamine under varying pH to fabricate composite films comprising polydopamine-modified boron nitride nanosheets and aramid sheets (BNNS@PDA/ANFS) by electrostatic assembly. The thermal conductivity of the composite rose to 36.9 W/m⋅K−1 with only 20 wt% filler. According to Density functional theory (DFT) simulation and interface thermal resistance calculation, the electrostatic assembly enhanced interface interactions and greatly reduced thermal resistance barrier. Furthermore, the optimal tensile strength of 304 MPa, is 2.32 times higher than pure ANFS film, accompanied by toughness of 33.2 MJ/m−3. These superior performances are the results of a synergistic strategy, combining interfacial and topological enhancements. This work provides an innovative approach to enhance effective filler contribution in matrix and underscores the significant potential of BNNS@PDA/ANFS composite films in applications related to heat management.

Interfacial effect investigation of lithium perchlorate-interacted oxygen-containing carbon paper

The lithium perchlorate-interacted oxygen-containing carbon paper (LiClO4-OCP) is designed to act as electroactive supercapacitor electrode substrates for the energy storage application. The OCP is fabricated through hydrothermal activation treatment of carbon paper in H2O2 reaction medium. The OCP is composed of graphite pitches with ultra-thin graphene structure of top layer, showing the improved graphitization degree. The LiClO4-OCP with the polarized electrostatic force-induced interfacial adsorption reveals much more intensive interaction than LiClO4-CP with van der Waals force-induced interfacial adsorption, contributing to promoting interfacial charge transfer of LiClO4-OCP. LiClO4-OCP reveals more effective interface charge transfer and more feasible electrolyte diffusion than LiClO4-CP, contributing to higher electrochemical double-layer capacitance. LiClO4-OCP with oxygen-containing groups conducts reversible redox process to supply additional Faradaic capacitance. Mean response current is increased from 0.10 ∼ 1.34 mA cm-2 for LiClO4-CP to 0.19 ∼ 2.31 mA cm-2 for LiClO4-OCP at scan rates of 5∼100 mV s-1, indicating the improved electrochemical activity of LiClO4-OCP. The cyclic voltammetry-based capacitance increases from 19.91 ∼ 13.01 mF cm-2 mF g-1 for LiClO4-CP to 37.76 ∼ 23.06 mF cm-2 for LiClO4-OCP. The galvanostatic charge/discharge-based capacitance decreases from 13.84 ∼ 3.97 mF cm-2 for LiClO4-CP to 29.71 ∼ 12.92 mF cm-2 for LiClO4-OCP. Density-functional theory-based simulation calculation proves LiClO4-OCP with such a short molecular distance is allowed to occur strong electrostatic interaction which is caused by the perchlorate ion-induced polarization of oxygen-containing groups. The LiClO4-OCP has lower interfacial energy, lower band gap and higher density of states at Fermi energy level than LiClO4-CP, indicating the improved interfacial interaction and electrical conductivity of LiClO4-OCP. The experimental measurement and theoretical calculation achieve the consistent results of higher electrochemical activity of LiClO4-OCP electrode substrate to present its superior capacitance performance.

Reactivity assessment of oligomeric systems associated with crystalline and amorphous cellulose for bioethanol production: a DFT study.

The production of bioethanol from renewable raw materials is a decisive factor in the economic development of many countries. However, the complexity of the processes and the numerous experimental variables involved require a deeper understanding of the chemical reactions that take place during bioethanol production to define optimal parameters. Here, we have employed density functional theory-based calculations to investigate the local reactivity of oligomeric systems by consideringcrystalline and amorphous cellulose models to better understand some details regarding pulp pretreatment processes. Our results evidence a higher chemical susceptibility of amorphous portions of cellulose to chemicals typically employed in acid hydrolysis. Additionally, we observed that glucose monomers coming from cellulose hydrolysis may undergo oxidation, leading to the formation of byproducts such as hydroxymethylfurfural (HMF), acetic acid, formic acid, and levulinic acid. The analysis of local chemical softness indexes indicated that cellulose hydrolysis may be associated with intermediate chemical steps. Finally, we investigated the influence of distinct solvents (dielectric constants) on the local reactivity of the systems, evidencing a relevant role of the solvent dielectric constant for cellulose degradation in glucose. Initial three-dimensional structures were constructed. Pre-optimizations were performed in a Hartree-Fock (HF) approach employing thePM7 semi-empirical hamiltonian. The structures were then re-optimized via density functional theory (DFT). The local reactivity study of the systems was conducted through the condensed-to-atoms Fukui indexes (CAFI). Systematic changes of the dielectric constants were also considered in geometry optimization and CAFI calculations to estimate the influence of solvents on the reactivity of the systems.

Coexisting Charge Density Waves in Twisted Bilayer NbSe2.

Twisted bilayers of 2D materials have emerged as a tunable platform for studying broken symmetry phases. While most interest has been focused toward emergent states in systems whose constituent monolayers do not feature broken symmetry states, assembling monolayers that exhibit ordered states into twisted bilayers can also give rise to interesting phenomena. Here, we use first-principles density-functional theory calculations to study the atomic structure of twisted bilayer NbSe2 whose constituent monolayers feature a charge density wave. We find that different charge density wave states coexist in the ground state of the twisted bilayer: monolayer-like 3 × 3 triangular and hexagonal charge density waves are observed in low-energy stacking regions, while stripe charge density waves are found in the domain walls surrounding the low-energy stacking regions. These predictions, which can be tested by scanning tunneling microscopy experiments, highlight the potential to create complex charge density wave ground states in twisted bilayer systems.

High-Temperature Solid-State Post-Synthetic Modification of Highly Luminescent Cu(I) Metallacycles toward New Luminescent Thermic Tracers.

A new luminescent Cu(I) tetrametallic metallacycle B is reported that features very rare semi-bridging aqua ligands. When heated markedly above room temperature, this compound undergoes a post-synthetic transformation in the solid-state, affording the new luminescent metallacycle C. Thermogravimetric analysis, IR spectroscopy and single-crystal X-ray diffraction reveal that this alteration preserves the gross tetrametallic macrocycle structure, but is caused by the release of the coordinated water molecules with the concomitant formation of cuprophilic interactions. This transition induces a shift from eye-perceived green (B) to blue (C) room-temperature luminescence for these molecular solids. Photophysical measurements and time-dependent density-functional theory calculations have been conducted to identify the origins of the emission properties lying in these structurally related assemblies, and suggest that thermally activated delayed fluorescence dominates the radiative relaxation pathways. This study highlights the innovative feature of Cu(I) derivatives, offering access to stimuli-sensitive materials that can witness, a posteriori, the exceeding of critical temperatures in their environment.

Surface Charge Regulation of Graphene by Fluorine and Chlorine Co-Doping for Constructing Ultra-Stable and Large Energy Density Micro-Supercapacitors.

Settling the structure stacking of graphene (G) nanosheets to maintain the high dispersity has been an intense issue to facilitate their practical application in the microelectronics-related devices. Herein, the co-doping of the highest electronegative fluorine (F) and large atomic radius chlorine (Cl) into G via a one-step electrochemical exfoliation protocol isengineered to actualize the ultralong cycling stability for flexible micro-supercapacitors (MSCs). Density functional theoretical calculations unveiled that the F into G can form the "ionic" C─F bond to increase the repulsive force between nanosheets, and the introduction of Cl can enlarge the layer spacing of G as well as increase active sites by accumulating the charge on pore defects. The co-doping of F and Cl generates the strong synergy to achieve high reversible capacitance and sturdy structure stability for G. The as-constructed aqueous gel-based MSC exhibited the superb cycling stability for 500,000 cycles with no capacitance loss and structure stacking. Furthermore, the ionic liquid gel-based MSC demonstrated a high energy density of 113.9mWhcm-3 under high voltage of up to 3.5V. The current work enlightens deep insights into the design and scalable preparation of high-performance co-doped G electrode candidate in the field of flexible microelectronics.

Geometric optimisation and structural properties of organic−inorganic halide perovskites from van der Waals density functional theory calculations

Organic–inorganic hybrid perovskites have attracted extensive attention in the photovoltaic field due to their unique photoelectric properties and low production costs. Using the density functional theory-based first-principles calculations, we reported the geometric optimisation and structural properties of halide perovskites using van der Waals density functional theory calculations. The strongly constrained and appropriately normed (SCAN) meta-GGA with the revised Vydrov-van Voorhis no-local correlation functional (SCAN + rVV10) are promising van der Waals density functional for solving van der Waals (vdW) interaction problems that many non-empirical semilocal functionals fail to include. We found the optimised structure parameters of halide perovskites based on the SCAN + rVV10 functionals are much closer to the experimental results than other functional including PBE and PBE + vdW-TS functionals, which provides the fundamental aspect for the theoretical calculations of surfaces, interfaces, optical properties, and structure-properties relationship.

Enhancing photocatalytic degradation of La-BiVO4 through bidirectional regulation of oxygen vacancy and the Mott-Schottky effect

Selective oxidation of photocatalysts is an important reaction, but catalytic capacity and reaction selectivity are usually contradictory. Herein, ultrafine La nanoparticles were introduced to regulate and control the coordination number and environment of Bi, and a catalyst was synthesized with oxygen defects (La-BiVO4) for Rhodamine degradation. Particularly, La-BiVO4 achieved a better reaction rate and selectivity under visible-light irradiation. The results revealed that the degradation rate of Rhodamine by La-BiVO4 reached 94.9 %. Additionally, the characterization and density functional theoretical calculation demonstrated that the Mott-Schottky effect in La-BiVO4 not only changed the BiVO4 electron density and boosted the visible-light-sensitivity, but also hastened the photogenerated charge migration and reduced the energy barrier. This study not only reveals the important role of optimizing single-atom coordination environment in generating free radicals in photocatalytic reactions, but also provides a reasonable degradation strategy for specific pollutants in the environment.

Effect of sites of doped Mg on the stability of lattice oxygen in lithium-rich manganese-based cathode materials

Elemental doping is considered as an effective method for altering the localized electronic structure of lattice oxygen in lithium-rich manganese-based oxides (LRMO) and enhancing their structural stability. However, the effect of doping heteroatoms at different sites on the oxygen redox is not clear. In this work, Mg is introduced into transition metals (TM) and lithium (Li) sites of LRMO at co-precipitation stage and lithiation stage to prepare LRMO-TM and LRMO-Li, respectively. The experimental results and density-functional theory calculations demonstrate that the oxygen release is reduced from 4.1653 nmol mg−1 of pristine to 3.3886 nmol mg−1 of LRMO-Li, and 2.7688 nmol mg−1 of LRMO-TM. The reduction of oxygen release of LRMO-Li is related to the formation of strong Mg-O interactions. Different from that, the lower oxygen release of LRMO-TM is mainly due to the reduction of electron holes in the O 2p state caused by the weaker Mn-O covalency, which effectively restricts the over-oxidization of oxygen. The capacity retention of LRMO-TM is 85.18 % at 0.2C after 200 cycles, which is higher than that of LRMO (78.63 %) and LRMO-Li (82.28 %). This work reveals the mechanism of enhancing lattice oxygen stability caused by Mg doping at different sites.

Mechanism insight into esterification of levulinic acid with methanol on H-Beta Zeolite: A DFT study

The esterification of levulinic acid (LA) to alkyl levulinate esters from biomass by heterogeneous acid catalysis is a potential chemical route for the sustainable production of high value-added products. Acidic zeolites are promising catalysts for this conversion due to their unique pore structures, high selectivity and strong acidity. In this work, we use Density Functional Calculations (DFT) to study the reaction mechanisms for the esterification of LA with MeOH on H-Beta zeolite. We have studied two mechanisms that we consider relevant to the formation of methyl levulinate in acidic zeolites, one involving an Eley-Rideal type mechanism and the other a Langmuir-Hinshelwood type mechanism. Since the activation energies of the rate-determining steps are quite similar, our results suggest that both mechanisms are favourable for this reaction, depending on how the LA and MeOH molecules are initially adsorbed.

Permeability of gas molecules through sub-nanometer nitrogen-terminated porous graphene membranes: A DFT study

We present a systematic theoretical investigation of gas permeability through single-layer nanoporous graphene membranes with N-terminated (pyridinic and mixed pyridinic/pyrrolic) pores for He, H2, N2, O2, CO, CO2, H2O, and CH4. Our study is based on density functional theory transition-state calculations and the kinetic theory of gasses. We systematically evaluate pores of varying sizes and shapes up to 5.7 Å in diameter. According to our findings, membranes with pores in the size regime (4.5 Å - 5.0 Å) may exhibit industrially acceptable permeance to several gas molecules and advanced selectivity. Notably, we found that, among a few others, a pore with the same topological features at the pore boundary as those of the characteristic pore of g-C3N4 carbon nitride, is particularly promising. In addition, membranes with larger pores, ∼5.5 Å - 5.7 Å, can effectively separate CH4 from the other molecules. Our findings support the advanced potential of single-layer graphene membranes with nitrogen-terminated sub-nanometer pores, for gas separation applications.

Hidden magnetism and split off flat bands in the insulator metal transition in VO2

Transition metal d-electron oxides with an odd number of electrons per unit cell are expected to form metals with partially occupied energy bands, but exhibit in fact a range of behaviors, being either insulators, or metals, or having insulator-metal transitions. Traditional explanations involved predominantly electron-electron interactions in fixed structural symmetry. The present work focuses instead on the role of symmetry breaking local structural motifs. Viewing the previously observed V-V dimerization in VO2 as a continuous knob, reveals in density functional calculations the splitting of an isolated flat band from the broad conduction band. This leads past a critical percent dimerization to the formation of the insulating phase while lowering the total energy. In VO2 this transition is found to have a rather low energy barrier approaching the thermal energy at room temperature, suggesting energy-efficient switching in neuromorphic computing. Interestingly, sufficient V-V dimerization suppresses magnetism, leading to the nonmagnetic insulating state, whereas magnetism appears when dimerization is reduced, forming a metallic state. This study opens the way to design novel functional quantum materials with symmetry breaking-induced flat bands.

Synthesis and crystal structure of acentric anhydrous beryllium carbonate Be(CO3).

The anhydrous alkaline earth metal carbonate Be(CO3) was synthesized in a laser-heated diamond anvil cell at moderate pressures and temperatures (20(2) GPa and 1500(200) K) by a reaction of BeO with CO2. It crystallizes in the acentric, trigonal space group P3121 with Z = 3. The crystal structure was obtained from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements were employed to verify the acentric space group symmetry. The crystal structure of Be(CO3) is characterized by the presence of isolated [CO3]2--groups and BeO4-tetrahedra. This is a new structure type and such a topology has not been observed in carbonates before. Be(CO3) can be recovered to ambient conditions and is not undergoing a phase transition during decompression.

Generic Approach to Intrinsic Magnetic Second-Order Topological Insulators via Inverted p-d Orbitals.

The integration of intrinsically magnetic and topologically nontrivial two-dimensional materials holds tantalizing prospects for exotic quantum anomalous Hall insulators and magnetic second-order topological insulators (SOTIs). Compared with their well-studied nonmagnetic counterparts, the pursuit of intrinsic magnetic SOTIs remains limited. In this work, we address this gap by focusing on p-d orbitals inversion, a fundamental but often overlooked phenomena in the construction of topological materials. We begin by developing a theoretical framework to elucidate p-d orbital inversion through a combined density-functional theory calculation and Wannier downfolding. Subsequently we showcase the generality of this concept in realizing ferromagnetism SOTIs by identifying two real materials with distinct lattices: 1T-VS2 monolayer in a hexagonal lattice and CrAs monolayer in a square lattice. We further compare it with other mechanisms requiring spin-orbit coupling and explore the similarities to topological Kondo insulators. Our findings establish a generic pathway toward intrinsic magnetic SOTIs.

Shape-Memory Effect and the Topology of Minimal Surfaces

Martensitic transformations, viewed as continuous mappings between triply periodic minimal surfaces (TPMSs), as suggested by Hyde and Andersson (Z. Kristallogr. 1986, 174, 225–236), are extended to include paths between the initial and final phases. Reversible transformations, which correspond to shape-memory materials, occur only if lattice points remain at flat points on a TPMS throughout a continuous transformation. For the shape-memory material NiTi, the density functional calculations by Hatcher et al. [Phys. Rev. B2009, 80, 144203] yield irreversible and reversible paths with and without energy barriers, respectively, in agreement with our theory. Although there are TPMSs for face-centered and body-centered cubic crystals for iron, the deformation between them is not reversible, in agreement with the non-vanishing energy barriers obtained from the density functional calculations of Zhang et al. (RSC Advances2021, 11, 3043–3048).

First-principles study of structural, electronic, and magnetic properties at the (0001)Cr2O3−(111)Pt interface

We perform first-principles density functional calculations to elucidate structural, electronic, and magnetic properties at the interface of (0001)Cr2O3−(111)Pt bilayers. This investigation is motivated by the fact that, despite the promise of Cr2O3−Pt heterostructures in a variety of antiferromagnetic spintronic applications, many key structural, electronic, and magnetic properties at the Cr2O3−Pt interface are poorly understood. We first analyze all inequivalent lateral interface alignments to determine the lowest energy interfacial structure. For all lateral alignments including the lowest energy one, we observe an accumulation of electrons at the interface between Cr2O3 and Pt. We find an unexpected reversal of the magnetic moments of the interface Cr ions in the presence of Pt compared to surface Cr moments in vacuum-terminated (0001)Cr2O3. We also find that the heterostructure exhibits a magnetic proximity effect in the first three Pt layers at the interface with Cr2O3, providing a mechanism by which the anomalous Hall effect can occur in (0001)Cr2O3−(111)Pt bilayers. Our results provide the basis for a more nuanced interpretation of magnetotransport experiments on (0001)Cr2O3−(111)Pt bilayers and should inform future development of improved antiferromagnetic spintronic devices based on the Cr2O3−Pt material system. Published by the American Physical Society 2024

Sulfurized Two-Dimensional Conductive Metal-Organic Framework as a High-Performance Cathode Material for Rechargeable Mg Batteries.

Rechargeable Mg batteries are a promising energy storage technology to overcome the limitations inherent to Li ion batteries. A critical challenge in advancing Mg batteries is the lack of suitable cathode materials. In this work, we report a cathode design that incorporates S functionality into two-dimensional metal-organic-frameworks (2D-MOFs). This new cathode material enables good Mg2+ storage capacity and outstanding cyclability. It was found that upon the initial Mg2+ insertion and disinsertion, there is an apparent structural transformation that crumbles the layered 2D framework, leading to amorphization. The resulting material serves as the active material to host Mg2+ through reduction and/or oxidation of S and, to a limited extent, O. The reversible nature of S and O redox chemistry was confirmed by spectroscopic characterizations and validated by density functional calculations. Importantly, during the Mg2+ insertion and disinsertion process, the 2D nature of the framework was maintained, which plays a key role in enabling the high reversibility of the MOF cathode.

Broad spectral response of Y-NaBi(MoO4)2@NaYF4:Yb, Tm photocatalysts for efficient degradation of ciprofloxacin: Upconversion mechanism and theoretical calculations

In this work, a novel Y-NaBi(MoO4)2@NaYF4:Yb, Tm composite was successfully synthesized for the first time by hydrothermal method. The lamellar Y-NaBi(MoO4)2 was dispersed on the surface of the hexagonal prism NaYF4:Yb, Tm without aggregation. The composite achieved a broad spectral response. The NaYF4:Yb, Tm absorbed near-infrared light and emitted ultraviolet and visible light by the energy transfer upconversion process. The emitted light was reabsorbed by Y-NaBi(MoO4)2 through the fluorescence resonance energy transfer process. Moreover, the doping of Y3+ ions enhanced the light response capability of the composite. The experimental results revealed that the photocatalytic degradation efficiency of ciprofloxacin (CIP) reached 96.2 % after 180 min of illumination under simulated sunlight. Meanwhile, the degradation pathways and attack sites of CIP were intensively investigated by liquid chromatography-mass spectrometry analysis and density functional theory theoretical calculations. The upconversion process, the separation of photogenerated carriers and rare earth metal ion doping all contributed to the high effective photodegradation. This work provided a new strategy for effective utilization of solar energy for the degradation of emerging pollutants to mitigate environmental pollution.

Enhancing the Electrocatalytic Hydrogenation of Furfural via Anion-Induced Molecular Activation and Adsorption.

The electrocatalytic hydrogenation (ECH) of furfural (FF) to furfuryl alcohol, which does not require additional hydrogen or high pressure, is a green and promising production route. In this study, we explore the effects of anions on FF ECH in two buffer electrolytes (KHCO3 and phosphate-buffered saline [PBS]). Anions influence the yield of furfuryl alcohol through molecular activation and adsorption. Molecular dynamics simulations show that bicarbonate is present in the first shell layer of the FF molecule and induces strong hydrogen bonding interactions. In contrast, hydrogen phosphate is present only in the second shell layer, resulting in weak hydrogen bonding interactions. Owing to the interfacial anions and hydrogen bonding, FF molecules exhibit strong flat adsorption on the electrode surface in the KHCO3 solution, while weak adsorption is observed in the PBS solution, as confirmed by operando synchrotron-radiation Fourier-transform infrared spectroscopy and in situ Raman spectroscopy. Density-functional theory calculations reveal that the overall anionic hydrogen bonding network promotes the activation of the carbonyl group in the FF molecule in KHCO3, whereas electrophilic activity is inhibited in PBS. Consequently, FF ECH demonstrates much faster kinetics in KHCO3, while it exhibits sluggish ECH kinetics and a severe hydrogen evolution reaction in PBS. This work introduces a new strategy to optimize the catalytic process through the modulation of the microenvironment.

Water orientation on platinum surfaces controlled by step sites.

In this work, the adsorption structure of deuterated water on the stepped platinum surface is studied under an ultra-high vacuum by using heterodyne-detected sum-frequency generation spectroscopy. On a pristine Pt(553), D2O molecules adsorbed at the step sites act as hydrogen bond (H-bond) donors to the adjacent terrace sites. This ensures the net D-down orientation at the terrace sites away from the steps. In particular, the pre-adsorption of oxygen atoms at the step sites significantly alters the D-down configuration. The oxygen pre-adsorption leads to a spontaneous dissociation of the post-adsorbed water molecules at the step to form hydroxyl (OD) species. Since the hydroxyl at the step acts as a strong H-bond acceptor, D2O at the terrace no longer maintains the D-down configuration and adopts flat-lying configurations, significantly reducing the number of D-down molecules at the terrace. Density-functional theoretical calculations support these pictures. This work demonstrates the critical role of steps in controlling the net orientation of the interfacial water and provides an important reference for future considerations of the reactions at electrochemical interfaces.