Ab Initio Density Functional Theory Research Articles

Investigating Elastic Deformation of Ordered Precipitates by Ab Initio-Informed Phase-Field Crystal Modeling

Ni-based superalloys, essential for high-temperature applications, derive strength from coherent second-order precipitates that impede dislocation motion through coherency misfit and elastic mismatch. This study employs multi-component phase-field crystal (PFC) simulations to explore the elastic deformation of such precipitates. Using a binary ordered square structure for the precipitate and a single species square structure for the matrix, elastic properties and lattice parameters are fitted to data from ab initio density functional theory calculations for Ni and Ni3Ti systems. Simulations reveal a smooth strain gradient across the matrix–precipitate interface with coherency misfit influenced by precipitate size and strain state. These findings highlight the utility of PFC simulations for understanding strain distribution and deformation in precipitate–matrix systems with the potential to offer insights for both experimental and computational studies.

Cavity-enhanced superconductivity in MgB2 from first-principles quantum electrodynamics (QEDFT)

Strong laser pulses can control superconductivity, inducing nonequilibrium transient pairing by leveraging strong-light matter interaction. Here, we demonstrate theoretically that equilibrium ground-state phonon-mediated superconductive pairing can be affected through the vacuum fluctuating electromagnetic field in a cavity. Using the recently developed ab initio quantum electrodynamical density-functional theory approximation, we specifically investigate the phonon-mediated superconductive behavior of MgB[Formula: see text] under different cavity setups and find that in the strong light-matter coupling regime its superconducting transition temperature T[Formula: see text] can be enhanced at most by [Formula: see text]10% in an in-plane (or out-of-plane) polarized and realistic cavity via photon vacuum fluctuations. The results highlight that strong light-matter coupling in extended systems can profoundly alter material properties in a nonperturbative way by modifying their electronic structure and phononic dispersion at the same time. Our findings indicate a pathway to the experimental realization of light-controlled superconductivity in solid-state materials at equilibrium via cavity materials engineering.

Modelling of (N-vinylcarbazole)/Fullerene nanoheterojunction for organic solar cells and photovoltaics applications – A DFT Approach

The current manuscript depicts the construction of a novel hybrid carbon nanomaterials with fascinating electronic and chemical properties and tunable energy bandgap of a nano heterojunction comprising (9-vinyl carbazole), VK and fullerene, C60. A comprehensive investigation of VK/C60 adsorption surface is conducted using ab-initio density functional theory calculations with van der Waals corrections (GGA+vdW) implemented. The novel nanoheterostructure interfaces synthesized by DFT methods have low-bandgap characteristics (1.112–1.223 eV), broaden absorption wavelengths and photovoltaic characteristics. This novel VK/C60 nanoheterostructure composites have finite bandgaps and good stability and, therefore, have promising applications for photovoltaic devices. Optoelectronic features of all three developed systems are recommended for future solar cell applications. The studies reveal that the VK/C60 nanoheterojunctions can behave as efficient electron donor-acceptor components in organic solar cells (OSCs) that make them potential candidates for the development of low-cost optoelectronic devices. The band gap values calculated in this work are low enough to make the nanoheterostructures exceedingly promising for photovoltaic applications.

Method and Implementation of Projected Hybrid Orbitals for Treating Multiple Covalent Bonds in Combined QM/MM Calculations.

The projected hybrid orbital (PHO) method for treatment of multiple boundary atoms introduces a novel solution for handling the covalent connection between quantum mechanical (QM) and molecular mechanical (MM) regions in QM/MM calculations. By projecting the QM basis, typically adequately large for computational accuracy, onto a secondary minimal basis set on the boundary atom, it preserves electronic interactions between the two regions without system-specific parameters. Applicable in both ab initio wave function theory and density functional theory, PHO has been shown to maintain structural and electronic integrity across various systems. It offers key advantages over traditional QM/MM methods, such as avoiding modification of MM charge distribution and energy corrections, while being flexible for biochemical systems and potentially broader QM/QM embedding frameworks.

A computational study of AlScN-based ferroelectric tunnel junction

Ferroelectric (FE) AlScN materials have been experimentally explored for memory and neuromorphic computing device applications. Here a computational study is performed to simulate the device characteristics and assess the performance potential of a ferroelectric tunnel junction (FTJ) based on AlScN. We parameterize an efficient k⋅p Hamiltonian from the complex band structure of AlScN from ab initio density-functional theory calculations to enable efficient quantum transport simulations of the FTJ device. Using a metal–FE–graphene structure enhances the barrier height modulation and the tunneling electroresistance (TER) ratio, compared to a metal–FE–semiconductor FTJ device structure. The barrier height modulation between ON and OFF states can reach ∼ 0.7eV with a FE polarization of 25 μC/cm2. Reducing the AlScN tunnel layer thickness is important for increasing the device ON current and reducing the read latency. The results indicate the importance of contact designs and FE layer thickness in the design of AlScN-based FTJ devices, and highlight the potential of AlScN FTJ for future memory device technology applications.

Tuning band gap and improving optoelectronic properties of lead-free halide perovskites FrMI3 (M = Ge, Sn) under hydrostatic pressure

In the field of optoelectronic applications, inorganic cubic halide perovskites have turned into a leading choice for commercialization. The physical properties of cubic FrMI3 (M = Ge, Sn) halide perovskites under pressure are explored at multiple pressures up to 10 GPa using ab initio Density-Functional Theory due to their significant importance. The structural accuracy, reflected in lattice parameters and unit cell volume, closely corresponds to previously reported data. FrGeI3 and FrSnI3 exhibited direct electronic band gaps of 0.65 eV and 0.46 eV with GGA-PBE functional, respectively, indicating their semiconducting nature at 0 GPa. The enhanced band gaps obtained employing the HSE06 potential are 1.61 eV and 1.28 eV for the corresponding perovskites. FrGeI3 and FrSnI3 shift from semiconducting to metallic states under pressures of 4.5 GPa and 3 GPa, respectively, thereby enhancing the conductivity. Pressure also improves optical functions, indicating both perovskites may be employed in high-efficiency optoelectronic devices that operate within the visible and ultra-violet (UV) range. At 10 GPa pressure, both FrGeI3 and FrSnI3 demonstrate the sharpest absorption spikes in the UV region, approximately at 2.61 × 105 cm−1 and 2.42 × 105 cm−1, respectively, resulting in sharp peaks in optical conductivity of approximately 5.98 1/fs for FrGeI3 and 5.49 1/fs for FrSnI3. FrGeI3 consistently outperforms FrSnI3, offering superior electronic and optical characteristics. Additionally, pressure modifies the mechanical features of entitled perovskites while conserving stability. The anisotropic and ductile properties become more pronounced under pressure. The outcomes of this study are expected to propel the advancement of lead-free optoelectronic devices, driving innovation in sustainable energy solutions.

Energetics of Point Defects in D0a Ag3Sn: First‐Principles Calculations

The Ag3Sn intermetallic compound is commonly found and acts as a strengthening factor in the key lead‐free solders based on Sn‐Ag‐Cu. The Ag3Sn phase exhibits also an asymmetric off‐stoichiometry, which necessitates the existence of constitutional point defects. The presence of point defects can, in general, sensitively affect the plastic deformation of materials and the strengthening role of Ag3Sn in particular. To understand the nature of the point defects and the compositional stability of Ag3Sn, the relaxed structures and the energies of single point defects (vacancies and antisite defects) in all three sublattices of Ag3Sn are calculated at 0 K using ab initio density functional theory (DFT) and the supercell method. The first‐principles‐based calculations predict that the AgSn antisite defect (Ag substitution for Sn) has the smallest enthalpy of formation, thus indicating that the AgSn antisite defect is the dominant point defect in Ag3Sn. The point defect concentrations as a function of Sn content are estimated using the DFT defect energies and the Wagner–Schottky model. The compositional dependence of the point defect concentrations gives new insights on the atomistic mechanisms of formation of nonstoichiometric Ag3Sn.

Cyclic and helical symmetry-informed machine learned force fields: Application to lattice vibrations in carbon nanotubes

We present a formalism for developing cyclic and helical symmetry-informed machine learned force fields (MLFFs). In particular, employing the smooth overlap of atomic positions descriptors with the polynomial kernel method, we derive cyclic and helical symmetry-adapted expressions for the energy, atomic forces, and phonons, i.e., lattice vibration frequencies and modes. We use this formulation to construct a symmetry-informed MLFF for carbon nanotubes (CNTs), where the model is trained through Bayesian linear regression, with the data generated from ab initio density functional theory (DFT) calculations performed during on-the-fly symmetry-informed MLFF molecular dynamics simulations of representative CNTs. We demonstrate the accuracy of the MLFF model by comparisons with DFT calculations for the energies and forces, and density functional perturbation theory calculations for the phonons, while considering CNTs not used in the training. In particular, we obtain a root mean square error of 1.4×10−4 Ha/atom, 4.7×10−4 Ha/Bohr, and 4.8 cm−1 in the energy, forces, and phonon frequencies, respectively, which are well within the accuracy targeted in ab initio calculations. We apply this framework to study phonons in CNTs of various diameters and chiralities, where we identify the torsional rigid body mode that is unique to cylindrical structures and establish laws for variation of the phonon frequencies associated with the ring modes and radial breathing modes. Overall, the proposed formalism provides an avenue for studying nanostructures with cyclic and helical symmetry at ab initio accuracy, while providing orders-of-magnitude speedup relative to such methods.

Perfluorinated Amines: Accelerating Lithium Electrodeposition by Tailoring Interfacial Structure and Modulated Solvation for High-Performance Batteries.

Modulating interfacial electrochemistry represents a prevalent approach for mitigating lithium dendrite growth and enhancing battery performance. Nevertheless, while most additives exhibit inhibitory characteristics, the accelerating effects on interfacial electrochemistry have garnered limited attention. In this work, perfluoromorpholine (PFM) with facilitated kinetics is utilized to preferentially adsorb on the lithium metal interface. The PFM molecules disrupt the solvation structure of Li+ and enhance the migration of Li+. Combined with the benzotrifluoride, a synergistic acceleration-inhibition system is formed. The ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculation of the loose outer solvation clusters and the key adsorption-deposition step supports the fast diffusion and stable interface electrochemistry with an accelerated filling mode with C─F and C─H groups. The approach induces the uniform lithium deposition. Excellent cycling performance is achieved in Li||Li symmetric cells, and even after 200 cycles in Li||NCM811 full cells, 80% of the capacity is retained. This work elucidates the accelerated electrochemical processes at the interface and expands the design strategies of acceleration fluorinated additives for lithium metal batteries.

Exploring the adsorption characteristics of quinoline derivatives on iron via ab initio DFT simulations and COSMO-RS profiles

Quinoline derivatives have been the subject of extensive research due to their excellent electronic properties and wide range of applications. This study conducts a comprehensive computational examination of the adsorption properties of substituted quinoline derivatives on Fe(110) surfaces. Four specific compounds, namely 2-amino-7-hydroxy-4-phenyl-1,4-dihydroquinoline-3-carbonitrile (QN1), 2-amino-7-hydroxy-4-(p-tolyl)-1,4-dihydroquinoline-3-carbonitrile (QN2), 2-amino-7-hydroxy-4-(4-methoxyphenyl)-1,4-dihydroquinoline-3-carbonitrile (QN3), and 2-amino-4-(4-(dimethylamino)phenyl)-7-hydroxy-1,4-dihydroquinoline-3-carbonitrile (QN4) were investigated using first-principles density functional theory (DFT) calculations along with COSMO-RS analysis for solvation properties. Our results revealed that the presence of functional groups significantly influence the adsorption strength on Fe(110) surfaces. Quinoline molecules have adsorbed on the iron surface through complex mechanisms involving physical interactions and charge transfer. Specifically, QN1 and QN4 showed strong physical interactions with iron atoms while QN2 and QN3 exhibited high affinity to coordinate with Fe atoms. The stability of coordinated quinolines was enhanced by a notable charge redistribution and bond formation as observed via projected density of states (PDOS). On the other hand, electron density difference (EDD) and electron localization function (ELF) iso-surfaces highlighted the critical role of van der Waals interactions, predominantly influenced by nitrogen atoms, in stabilizing the adsorbed molecules. The COSMO-RS analysis elucidated the solvation characteristics, emphasizing the importance of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) in the interaction of quinolines with water molecules. Overall, this study provides crucial insights into the molecular mechanisms underlying the corrosion inhibition properties of quinoline derivatives, emphasizing the influence of functional groups and solvation effects on adsorption behavior and stability.

A new homologous series of semi-conducting liquid crystals based on phenyl-anthracene: synthesis and effect of the alkyloxy terminal chain on charge transport and photoconductive properties.

π-Conjugated systems are the key to the charge transport properties of organic semiconductors. Four multifunctional mesogenic materials were designed and synthesised from 2-amino anthracene and para-hydroxybenzaldehyde. Each material contains a central, rigid phenyl-anthracene core and one flexible alkyloxy chain with different lengths based on the concept of combining liquid crystal (LC) materials featuring facile processability, highly ordered alignment, and effective charge transport. (E)-N-(Anthracen-2-yl)-1-(4-(alkyloxy)phenyl) methanimine (n-OPIA) with n = 8, 10, 12, and 16 was chemically characterized by nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. Their thermal behaviours were performed by means of differential scanning calorimetry and polarised optical microscopy and showed differences in mesomorphic behaviours with respect to the alkyloxy chain length. Concerning their frontier molecular energy levels, they were studied by optical spectroscopy and cyclic voltammetry and compared to values obtained via ab initio density-functional theory (DFT) calculations. LC field-effect transistors (LC-FETs) using a solvent vapour enhanced drop casting based n-OPIA material showed efficient electrical parameters and interesting photoconductive properties, indicating their potential applications in multifunctional integrated devices. As the alkyloxy chain length of the n-OPIA compounds increased, the hole mobility, on/off current ratio, and responsivity decreased. The 8-OPIA homologue exhibits a mobility one order of magnitude larger than the previously studied homologue, namely 10-OPIA.

Origin of the High-Frequency Shoulder in the Raman Spectra of CdSe Quantum Dots.

The origin of the high-frequency shoulder (HFS) observed above the longitudinal optical (LO) peak around 230 cm-1 in the Raman spectra of CdSe quantum dots (QDs) has been the subject of intense debate. We use state-of-the-art ab initio density functional theory applied to small CdSe QDs with various realistic surface passivations and find an intense Raman signal around 230 cm-1, which corresponds to a stretching vibration of a defective 2-fold coordinated Se atom. We interpret this signal as being the origin of the HFS. Since the signal disappears in fully passivated and defect-free (magic size cluster) structures, it can be used as a fingerprint to distinguish defective from nondefective structures.

CO oxidation on single Pt atom supported by two-dimensional ZnO monolayer: Reaction mechanism and precursor activation

CO oxidation is an effective solution for controlling CO emissions, and supported single-atom catalysts have shown excellent catalytic reactivity for chemical reactions. CO oxidation on a single Pt atom supported by a two-dimensional ZnO monolayer is investigated by combing ab initio molecular dynamics and density functional theory calculations. Seven reaction mechanisms are identified, including two new trimolecular Elie-Riedel mechanisms; six of them, except for the Mars-van Krevelen mechanism, have rate-limiting step energy barriers between 0.31 and 0.47 eV, which is lower than the experimental activation barrier of 0.81 eV on single Pt atoms supported by bulk ZnO, and is much lower than that of about 1.0 eV on Pt(111) surface. Furthermore, two preferred reaction mechanisms are discovered, an Eley-Rideal mechanism and a trimolecular Eley-Rideal mechanism, both of which have rate-limiting step energy barriers as low as 0.31 eV. Our results show that the more antibonding orbitals are filled in the reaction precursor, the higher its activation level. Activation of precursors plays an important role in CO oxidation and leads to different mechanisms. These results provide insights into the design of efficient single-atom catalysts supported by two-dimensional materials for the removal of CO pollutants.

Linking Ab initio density functional theory with modelling reaction microkinetics to understand catalytic fatty acids hydro-deoxygenation intermediate species selectivity

Catalyst surfaces enable the catalytic reactions via binding of substrates and lowering the reaction barriers to obtain the desired products. Separating the binding process from the reaction barriers enables us the understanding of surface properties and enables the reaction engineering strategies such as choice of solvents or functional groups protections. Through the modelling of the hydrodeoxygenation (HDO) of fatty acids, namely Stearic, Oleic, Linoleic, Myristic and Decanoic acid we show why the alkanes are the ideal solvent choice for NiMoS catalyst, why the alcohols side products form, regardless of the kinetic constant indicating fast dehydration, why the aldehydes intermediates are rarely detected and why hydrogenation of double bonds supersedes other kinetics events. We confirm the DFT calculations by integrating them into the kinetic model which confirms that the obtained results are sensible and usable in reaction engineering. The results are supported by the detailed characterization of the NiMoS catalyst.

Analysis on the shape of α-Sn CQDs

In the search for materials alternate to bulk HgCdTe for high performance infrared imaging applications, colloidal quantum dots (CQDs), particularly HgTe CQDs, have gained traction owing to acceptable detector performance with easy preparation and low cost. In this article, we evaluate α-Sn CQDs, an environmentally less reactive and less toxic alternative to HgTe, for infrared sensing applications. Ab initio density functional theory calculations are used to study the shape-dependent stability, electronic bandgap, and absorption coefficient of α-Sn CQD nanoparticles (NPs). We consider three possible CQD shape constructions—Wulff, shell-by-shell, and spherical. The CQD of Wulff construction is predicted to be the most stable. However, we find that the size, not the shape, of the NP has a strong effect on the bandgap and absorption coefficient. Consequently, a sharp absorption edge is expected even in an ensemble of CQDs with different shapes. Importantly, the shape determines the position of the band edges with respect to vacuum, and thus offers a possibility of choosing the shape to improve alignment with the energy levels of ligands to enable efficient drift transport, instead of a slower and less efficient hopping transport.

Ab initio informed solute drag assessment for ferritic steels

Linking atomistic information on solute interactions with microstructure evolution is a key challenge for predictive modelling of chemistry effects on material properties. The objective of the present work is to provide a link between grain boundary segregation energies with GB migration kinetics on the example of recrystallization in multi-component ferritic steels. For that purpose, the segregation of 64 elements from the periodic table to a representative grain boundary is computed with ab initio density functional theory. To connect this data to grain boundary migration kinetics, the solute trend parameter from a simplified solute drag treatment is employed. The solute trend parameter for individual solutes is presented, which highlights solutes with large impact on grain boundary migration. Furthermore, an extension of the solute trend parameter is introduced that allows to evaluate the solute drag potential of realistic steel compositions. The necessity to include solute co-segregation, site competition, and precipitation effects is shown in a comparison to experimental data on recrystallization kinetics. The comparison to experimental data demonstrates the qualitative predictability of recrystallization kinetics by the extended solute trend parameter.

Nonprecious Single Atom Catalyst for Methane Pyrolysis.

The development of a suitable catalytic system for methane pyrolysis reactions requires a detailed investigation of the activation energy of C-H bonds on catalysts, as well as their stability against sintering and coke formation. In this work, both single-metal Ni atoms and small clusters of Ni atoms deposited on titanium nitride (TiN) plasmonic nanoparticles were characterized for the C-H bond activation of a methane pyrolysis reaction using ab initio spin-polarized density functional theory (DFT) calculations. The present work shows the complete reaction pathway, including energy barriers for C-H bond activation and dehydrogenated fragments, during the methane pyrolysis reaction on catalytic systems. Interestingly, the C-H bond activation barriers were low for both Ni single-atom and Ni-clusters, showing the energy barriers of ~1.10 eV and ~0.88 eV, respectively. Additionally, single-atom Ni-TiN showed weaker binding to adsorbates, and a net endothermic reaction pathway indicated that the single-atom Ni-TiN was expected to resist coke formation on its surface. However, these Ni single-atom catalysts can sinter, aggregate into a small cluster, and form a coke layer from the highly exothermic reaction pathway that the cluster takes despite the facile reaction pathway.

Thermal Behavior and Infrared Absorbance Bands of Citric Acid

Citric acid is widely used in the Food and Pharmaceutical Industry. Various issues regarding its thermal behavior and infrared spectrum require clarification. Here, we studied citric acid monohydrate (raw, heated, freeze-dried and recrystallized from D2O) via Differential Scanning Calorimetry, Thermogravimetric Analysis, Infrared Spectroscopy, and antioxidant capacity assay. Also, we used ab initio Density Functional Theory calculations for further supporting the interpretations of the experimental results. Citric acid monohydrate exhibits desolvation inability and upon heating does not dehydrate but esterifies. Nor by freeze drying can it be dehydrated. The heated sample is not anhydrous, it exhibits melting inability, and any fluidization occurs simultaneously with decomposition. In other words, the interpretations regarding the two endothermic peaks in the DSC curve of citric acid that have been attributed to water evaporation and melting are not correct. The increase in the molecular weight due to esterification is most likely responsible for the increased antioxidant/chelation capacity of the heated sample. We concluded that what we call citric acid monohydrate and anhydrous do not exist in a pure form (in the solid state) and actually are mixtures of different compositions of citric acid, water and a citric acid oligomer that is produced through esterification. The esterification reaction seems to be able to proceed easily under mild heating or even at room temperature. The presence of the ester oligomer and water affect the infrared spectrum of citric acid monohydrate and anhydrous and is responsible for the existence of multiple peaks in the C=O stretching region, which partially overlaps with the water H-O-H bending vibration. The insights presented in this work could be useful for optimizing the design, performance and quality of food and drug products in which citric acid is used.

Unraveling the Stability and Magnetic Properties of Bis-Hydrated Mn(II) Complexes via Tailored Ligand Design.

Exploring the electronic structure and dynamic behavior of Mn(II) complexes reveals fascinating magnetic properties and prospective biomedical applications. In this study, we investigate the solvent phase dynamics of heptacoordinated Mn(II) complexes through ab initio molecular dynamics simulations and density functional theory (DFT) calculations with effectively varying temperatures. We observed that the complex with high stability ([Mn(pmpa)(H2O)2]) remains relatively rigid as the temperature increases to 90 °C, with only a minor change in its radial distribution functions (RDFs), compared to the RDF peaks at 25 °C. To elucidate the impact of halogens on the magnetic anisotropy of seven-coordinated Mn(II) complexes, we performed both DFT and multireference calculations. This shows that the zero-field splitting (ZFS) parameter D follows the order D(I)> D(Br)> D(Cl). We observed a significant increase in the D-value following the substitution of soft Se-donors in the equatorial position and heavier halogens in the axial position. The D-value of halogen derivatives of Se-analogues varies in the order of D(Cl) < D(I) < D(Br), deviating from the regular spectrochemical series with the discrepancy between the covalency of the Mn(II)-Se bond and the ligand field strength. We anticipate that this study will enhance our understanding of the solvent phase dynamics and structural aspects of ZFS in various Mn(II) complexes with different electronic environments.

Ab initio investigation of the structural, mechanical, electronic, thermodynamic, and optical properties of V2FeNiGe2 and Hf2FeNiSb2 double half-Heusler compounds

In the present work, using ab initio density-functional theory methods based on the Quantum ESPRESSO package, we have investigated the structural, elastic, electronic, and optical properties of 18-electron V2FeNiGe2 and Hf2FeNiSb2 double half-Heusler alloys. The calculated elastic properties suggest a ductile behavior with metallic bonding for V2FeNiGe2 and a brittle behavior with covalent bonding for Hf2FeNiSb2. The thermodynamic properties (Debye temperature, melting temperature) are also predicted and discussed for the studied alloys. The alloys are found to be semiconducting with indirect band gaps of 0.53 eV for V2FeNiGe2 and 0.47 eV for Hf2FeNiSb2. We also computed and analyzed their optical properties (dielectric function, optical conductivity, refractive index, absorption index, and reflectance) and our calculations suggest that both materials have high absorption coefficient and optical conductivity in the UV as well as visible region. The results make them potential candidates for the manufacture of opto-electronic devices.