Ab Initio Calculations Research Articles

Theoretical Investigation on One-Electron ϕ···ϕ Bonding in Diuranium Inverse Sandwich U2B6 Complex Enabled by a B6 Ring.

Traditional σ, π, and δ types of covalent chemical bonding have been extensively studied for nearly a century. In contrast, ϕ-type bonding involving nf (n = 4, 5) orbitals has received less attention due to their high contraction and minimal orbital overlap. Herein, we theoretically predict a singly occupied ϕ···ϕ bonding between two 5f orbitals, facilitated by B6 group orbitals in the hexa-boron diuranium inverse sandwich structure of U2B6. From ab initio quantum chemical calculations, the global minimum structure has a septuplet state with D6h symmetry. Chemical bonding analyses reveal that the 5f and 6d atomic orbitals of the two uranium atoms interact with the ligand orbitals of the central B6 ring, exhibiting favorable energy matching and symmetry compatibility to form delocalized σ-, π-, δ-, and ϕ-type bonding orbitals. Notably, even though the ϕ···ϕ bonding orbital is singly occupied, it still has a significant role in stability and cannot be overlooked. Furthermore, the U2B6 cluster model can be viewed as a building block of UB2 solid materials from both geometric and electronic perspectives. This work predicts the first example of ϕ···ϕ bonding, highlighting the complexity and diversity of chemical bonds formed in actinide boride clusters.

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.

Two-Gap Superconductivity and the Decisive Role of Rare-Earth d Electrons in Infinite-Layer Nickelates.

We present a theoretical prediction of a phonon-mediated two-gap superconductivity in infinite-layer nickelates Nd_{1-x}Sr_{x}NiO_{2} by performing abinitio GW and GW perturbation theory calculations. Electron GW self-energy effects significantly alter the characters of the two-band Fermi surface and enhance the electron-phonon coupling, compared with results based on density functional theory. Solutions of the fully k-dependent anisotropic Eliashberg equations yield two dominant s-wave superconducting gaps-a large gap on a band of rare-earth Nd d and interstitial orbital characters and a small gap on a band of transition-metal Ni d character. Increasing hole doping induces a non-rigid-band response in the electronic structure, leading to a rapid drop of the superconducting T_{c} in the overdoped regime in agreement with experiments.

Cryogenic temperatures promote the pressure-induced polymorphic transition in CoCrFeMnNi high entropy alloy

Pressure-induced polymorphism has recently been demonstrated in several high entropy alloys. This offers a new window into the much-debated issue of phase selection and stability in these systems. Here, we examine the effect of cryogenic temperatures on the pressure-induced transition from face centered cubic to hexagonal close-packed structures of the prototype CoCrFeMnNi (Cantor) alloy. We observe a reduction in the critical pressure for the onset of the polymorphic transition as the temperature decreases, confirming the progressive stabilization of the hexagonal phase with decreasing temperature previously predicted by ab initio calculations accounting for magnetic interactions. We argue that in situ high-pressure experiments at cryogenic temperatures, which suppress time-dependent transformation triggered at higher temperatures, present a unique opportunity to significantly improve our understanding of these complex alloys.

Orbital magnetism through inverse Faraday effect in metal clusters

Abstract In view of the recent increased interest in light-induced manipulation of magnetism in nanometric length scales this work presents metal clusters as promising elementary units for generating all-optical ultrafast magnetization. We perform a theoretical study of the opto-magnetic properties of metal clusters through ab-initio real-time (RT) simulations in real-space using time-dependent density functional theory (TDDFT). Through ab-initio calculations of plasmon excitation with circularly polarized laser pulse in atomically precise clusters of simple and noble metals, we discuss the generation of orbital magnetic moments due to the transfer of angular momentum from light field through optical absorption at resonance energies. Notably, in the near-field analysis we observe self-sustained circular motion of the induced electron density corroborating the presence of nanometric current loops which give rise to orbital magnetic moments due to the inverse Faraday effect (IFE) in the clusters. The results provide valuable insights into the quantum many-body effects that influence the IFE-mediated light-induced orbital magnetism in metal clusters depending on its geometry and chemical composition. At the same time, they explicitly demonstrate the possibility for harnessing magnetization in metal clusters, offering potential applications in the field of all-optical manipulation of magnetism.

Reaction Rate Rules of Intramolecular H-Migration Reaction Class for RIORIIOO·Radicals in Ether Combustion.

The intramolecular H-migration reaction of RIORIIOO· radicals constitute a key class of reactions in the low-temperature combustion mechanism of ethers. Despite this, there is a dearth of direct computations regarding the potential energy surface and rate constants specific to ethers, especially when considering large molecular systems and intricate branched-chain structures. Furthermore, combustion kinetic models for large molecular ethers generally utilize rate constants derived from those of structurally similar alcohols or alkane fuels. Consequently, chemical kinetic studies involve the calculation of energy barriers and rate rules for the intramolecular H-migration reaction class of RIORIIOO· radicals, which are systematically conducted using the isodesmic reaction method (IRM). The geometries of the species participating in these reactions are optimized, and frequency calculations are executed using the M06-X method in tandem with the 6-31+G(d,p) basis set by the Gaussian 16 program. Moreover, the M06-2X/6-31+G(d,p) method acts as the low-level ab initio method, while the CBS-QB3 method is utilized as the high-level ab initio method for calculating single-point energies. Rate constants at the high-pressure-limit are computed based on the reaction class transition state theory (RC-TST) by ChemRate program, incorporating asymmetric Eckart tunneling corrections for intramolecular H-migration reactions across a temperature range of 500 to 2000 K. It was found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the rate constants of the H-migration reaction for RIORIIOO· radicals diverge from those of comparable reactions in alkanes and alcohol fuels. There are significant disparities in energy barriers and rate constants across the entire reaction classes of the H-migration reaction for RIORIIOO· radicals, necessitating the subdivision of the H-migration reaction into subclasses. Rate rules are established by averaging the rate constants of representative reactions for each subclass, which is pivotal for the advancement of accurate low-temperature combustion reaction mechanisms for ethers.

Tensor factorization in ab initio many-body calculations

Tensor factorization in ab initio many-body calculations

Adsorptive Shield Derived Cathode Electrolyte Interphase Formation with Impregnation on LiNi0.8Mn0.1Co0.1O2 Cathode: A Mechanism-Guiding-Experiment Study.

Lithium difluoro(oxalate) borate (LiDFOB) contributes actively to cathode-electrolyte interface (CEI) formation, particularly safeguarding high-voltage cathode materials. However, LiNixCozMnyO2-based batteries benefit from the LiDFOB and its derived CEI only with appropriate electrolyte design while a comprehensive understanding of the underlying interfacial mechanisms remains limited, which makes the rational design challenging. By performing ab initio calculations, the CEI evolution on the LiNi0.8Co0.1Mn0.1O2 has been investigated. The findings demonstrate that LiDFOB readily adheres to the cathode via semidissociative configuration, which elevates the Li deintercalation voltage and remains stable in solvent. Electrochemical processes are responsible for the subsequent cleavage of B-F and B-O bonds, while the B-F bond cleavage leading to LiF formation is dominant in the presence of adequate Li+ with a substantial Li intercalation energy. Thus, impregnation is established as an effective method to regulate the conversion channel for efficient CEI formation, which not only safeguards the cathode's structure but also counters electrolyte decomposition. Consequently, in comparison to utilizing LiDFOB as an electrolyte additive, employing LiDFOB impregnation in the NCM811/Li cell yields significantly improved cycling stability for over 2000 h.

Nature of Scapolite Color: Ab Initio Calculations, Spectroscopy, and Structural Study

The article describes the results of a comprehensive study of the extra-framework components of scapolites using quantum–chemical calculations, electronic and vibrational spectroscopy, and single-crystal X-ray diffraction and crystal structure refinement. The ab initio calculations were performed using an embedded-cluster approach of extra-framework components in various cation surroundings. As a result, through comparing the experimental and ab initio calculation results, the energies of the electronic and vibrational transitions of various extra-framework components (CO3)2−, (CO3)·−, S3·−, S2·−—as well as the role of these components in the process of the lowering of the symmetry—were determined for scapolites belonging to the marialite–meionite solid–solution series. The nature of the various colors of the scapolites has also been established. Colors from purple to blue are a result of the presence of radiation-induced pairs of defects: carbonate radical anions (CO3)·− and F-centers. However, polysulfide S3·− radical anions are found in some violet scapolites.

A unified moment tensor potential for silicon, oxygen, and silica

Si and its oxides have been extensively explored in theoretical research due to their technological importance. Simultaneously describing interatomic interactions within both Si and SiO2 without the use of ab initio methods is considered challenging, given the charge transfers involved. Herein, this challenge is overcome by developing a unified machine learning interatomic potentials describing the Si/SiO2/O system, based on the moment tensor potential (MTP) framework. This MTP is trained using a comprehensive database generated using density functional theory simulations, encompassing diverse crystal structures, point defects, extended defects, and disordered structure. Extensive testing of the MTP is performed, indicating it can describe static and dynamic features of very diverse Si, O, and SiO2 atomic structures with a degree of fidelity approaching that of DFT.

Melting temperature of iron under the Earth’s inner core condition from deep machine learning

Constraining the melting temperature of iron under Earth’s inner core conditions is crucial for understanding core dynamics and planetary evolution. Here, we develop a deep potential (DP) model for iron that explicitly incorporates electronic entropy contributions governing thermodynamics under Earth’s core conditions. Extensive benchmarking demonstrates the DP’s high fidelity across relevant iron phases and extreme pressure and temperature conditions. Through thermodynamic integration and direct solid–liquid coexistence simulations, the DP predicts melting temperatures for iron at the inner core boundary, consistent with previous ab initio results. This resolves the previous discrepancy of iron’s melting temperature at ICB between the DP model and ab initio calculation and suggests the crucial contribution of electronic entropy. Our work provides insights into machine learning melting behavior of iron under core conditions and provides the basis for future development of binary or ternary DP models for iron and other elements in the core.

Magnetization and phase transformation in Fe-Ga and Fe-Ge alloys

The magnetic properties and structural states of Fe-Ga and Fe-Ge alloys, known for their large magnetostriction, have been investigated. Experimental characterizations are supported by ab initio calculations and Monte Carlo simulations to reveal the complex interplay between magnetic properties and structural changes. Our findings are in agreement with previous investigations and show that the Curie temperature (TC) of these alloys changes gradually with increasing alloying element concentration while the A2 solid solution is being realized. Further alloying of Fe-Ga leads to the transition from a single-phase to a two-phase A2 + D03 state and results in two distinct TC values. At the same time Fe-Ge shows a more complex behavior with several phase transitions influencing the magnetic ordering temperatures. Theoretical calculations suggest a significant correlation between the magnetic moments, exchange interactions, and observed TC trends. It is shown that the D03 phase is characterized by the lowest TC among other phases. Using Monte Carlo simulations, we found that in ferromagnetic state of Fe-Ge alloy the D03 ordering develops homogeneously, while in Fe-Ga it follows a nucleation and growth scenario.

Ab initio computations from 78Ni towards 70Ca along neutron number N = 50

We present coupled-cluster computations of nuclei with neutron number N=50 “south” of 78Ni using nucleon-nucleon and three-nucleon forces from chiral effective field theory. We find an erosion of the magic number N=50 toward 70Ca manifesting itself by an onset of deformation and increased complexity in the ground states. For 78Ni, we predict a low-lying rotational band consistent with recent data, which up until now has been a challenge for ab initio nuclear models. Ground states are deformed in 76Fe, 74Cr, and 72Ti, although the spherical states are too close in energy to unambiguously identify the shape of the ground state within the uncertainty estimates. In 70Ca, the potential energy landscape from quadrupole-constrained Hartree-Fock computations flattens, and the deformation becomes less rigid. We also compute the low-lying spectra and B(E2) values for these neutron-rich N=50 nuclei.

In-depth investigation of the iodine-nitrogen interaction mechanism using ab initio and density functional theory calculations

In this paper, wesystematicallyinvestigate the interactions of I2with several representative nitrogen-containing building units (NBUs) using high-precisionabinitioand density functional theory calculations. Our findings reveal that the binding strengths of I2with NBUs arepositively correlated withthe hybridization degreesof N-2pelectrons. Further energy analysesindicate that the I-N orbital interaction determinesthe binding strength to a great extent. Especially for I2@NBU(sp3), itsσnbinding orbital formed by theσorbital of I2and the n orbital of NBU(sp3) exhibits nearly perfect orbital overlap. QTAIM analyses identifythe unique partially covalent feature of I-N bonds in I2@NBU(sp2/sp3) and the pure ionic feature in I2@NBU(sp). The I-N orbital interactions lead to remarkableelectron reorganizations in I2@NBUs. Moreover, we demonstrate thatthe binding strengths between NBUs and I2 can be effectively regulated through introducing electron-donating/electron-withdrawing functional groups. This study deepens the fundamental understanding of iodine coordination chemistry.

Reassessment of the High-Temperature Oxidation of Di Ethyl Ether through Ab Initio Calculations.

Recent investigations of diethyl ether (DEE) high-temperature pyrolysis and fuel-rich oxidation have highlighted the failure of existing kinetic models to describe experimental CO production. The DEE high-temperature pyrolysis and oxidation chemistry is thus investigated through ab initio calculations. Geometries, frequencies, and hindered-rotor potentials of reactants, products, and transition states of key reactions (fuel decomposition radical decomposition and H-abstraction reactions) are calculated with the B2PLYP-D3/def2-TZVPD method, whereas final energies are refined using CCSD(T)/aug-cc-pV(D,T)Z. Temperature- and pressure-dependent rate constants are then derived from either canonical transition state theory (CTST) or ME/RRKM analysis with the inclusion of tunneling effect and hindered-rotor corrections and compared to experimental measurements when available as well as to previously suggested values. This new information is then merged with a C0-C3 core chemistry model and a low-temperature chemistry DEE subset from the literature to propose a new kinetic model for the combustion of DEE. This model is tested successfully against a large database related to the high-temperature oxidation and pyrolysis chemistry of DEE, including ignition delay times, shock tube speciation data, time-resolved CO profiles, laminar flame speeds, flame structures, and jet-stirred reactor data.

Unveiling Inequality of Atoms in Ultrasmall Pt Clusters: Oxygen Adsorption Limited to the Uppermost Atomic Layer

The concept of preferential atomic and molecular adsorption site is of primary relevance in heterogeneous catalysis. In the case of ultrasmall size‐selected clusters, distinguishing the role played by each atom in a reaction is extremely challenging due to their reduced size and peculiar structures. Herein, it is revealed how the inequivalent atoms composing graphene‐supported Pt12 and Pt13 clusters behave differently in the photoinduced dissociation of O2, with only those in the uppermost layer of the clusters being involved in the reaction. In this process, the epitaxial graphene support plays a fundamental active role: its corrugation and pinning induced by the presence of the clusters are crucial for defining the preferential adsorption site on the Pt atomic agglomerates, facilitating the lateral diffusion of physisorbed oxygen at a distance that induces its selective adsorption in the topmost layer of the clusters, and inducing an inhomogeneous charge distribution within the clusters which directly affects the O2 adsorption. The inhomogeneous oxidation of the clusters is resolved by means of synchrotron‐based X‐ray photoelectron spectroscopy and supported by ab initio density functional theory calculations. The possibility to identify the active sites on Pt clusters induced by cluster–support interactions has the potential to enhance the experimentally supported design of nanocatalysts.

Scalable Layer-Controlled Oxidation of Bi2O2Se for Self-Rectifying Memristor Arrays With sub-pA Sneak Currents.

Smart memristors with innovative properties are crucial for the advancement of next-generation information storage and bioinspired neuromorphic computing. However, the presence of significant sneak currents in large-scale memristor arrays results in operational errors and heat accumulation, hindering their practical utility. This study successfully synthesizes a quasi-free-standing Bi2O2Se single-crystalline film and achieves layer-controlled oxidation by developing large-scale UV-assisted intercalative oxidation, resulting β-Bi2SeO5/Bi2O2Se heterostructures. The resulting β-Bi2SeO5/Bi2O2Se memristor demonstrates remarkable self-rectifying resistive switching performance (over 105 for ON/OFF and rectification ratios, as well as nonlinearity) in both nanoscale (through conductive atomic force microscopy) and microscale (through memristor array) regimes. Furthermore, the potential for scalable production of self-rectifying β-Bi2SeO5/Bi2O2Se memristor, achieving sub-pA sneak currents to minimize cross-talk effects in high-density memristor arrays is demonstrated. The memristors also exhibit ultrafast resistive switching (sub-100ns) and low power consumption (1.2 pJ) as characterized by pulse-mode testing. The findings suggest a synergetic effect of interfacial Schottky barriers and oxygen vacancy migration as the self-rectifying switching mechanism, elucidated through controllable β-Bi2SeO5 thickness modulation and theoretical ab initio calculations.

Lanthanide-Dependent Photochemical and Photophysical Properties of Lanthanide-Anthracene Complexes: Experimental and Theoretical Approaches.

The structural, photophysical, and photochemical properties of Ln(depma)(hmpa)2(NO3)3 (Ln = La, Ce, Nd, Sm, Eu, Tb, Ho, Er, and Yb) complexes 1-Ln were investigated with a multidisciplinary approach involving synthesis, photocycloaddition-based crystal engineering, spectroscopic analytical techniques and quantum chemical ab initio calculations. Depending on the Ln3+ ion the isostructural 1-Ln complexes exhibit quite different behavior upon excitation at 350-400 nm. Some 1-Ln complexes (Ln = La, Ce, Sm, Tb, Yb) emit a broad and strong band near 533 nm arising from paired anthracene moieties, whereas others (Ln = Nd, Eu, Ho, Er) do not. 1-Eu is not emissive at all, whereas 1-Nd, 1-Ho, and 1-Er exhibit a Ln3+ based luminescence. Upon irradiation with 365 nm ultraviolet (UV) light 1-Ln (Ln = La, Ce, Sm, Tb, Yb) dimerize by means of a photochemically induced [4 + 4] cycloaddition of the anthracene moieties, whereas 1-Ln (Ln = Nd, Eu, Ho, Er) remain monomers. We propose three models, based on the matching of the energy levels between the Ln3+ ion and the paired or dimerized anthracene units in the energy-resonance crossing region, as well as on internal conversion-driven and intersystem crossing-driven energy transfer, which explain the Ln3+ ion regulated photophysics and photochemistry of the 1-Ln complexes.

Pyrolytic conversion of glucose into hydroxymethylfurfural and furfural: Benchmark quantum-chemical calculations.

Quantum chemical methods have been intensively applied to study the pyrolytic conversion of glucose into hydroxymethylfurfural (HMF) and furfural (FF). Herein, we collect the most relevant mechanistic proposals from the recent literature and organize them into a single reaction network. All the transition structures (TSs) and intermediates are characterized using highly accurate ab initio methods and the possible reaction pathways are assessed in terms of the Gibbs energies of the TSs and intermediates with respect to β-glucopyranose, selecting a 2D ideal-gas standard state at 773 K to represent the pyrolysis conditions. Several pathways can lead to the formation of both HMF and FF passing through rate-determining TSs that have ΔG‡ values of ~49-50 kcal/mol. Both water-assisted mechanisms and nonspecific environmental effects have a minor impact on the Gibbs energy profiles. We find that the HMF → FF + CH2O fragmentation has a small ΔrxnG value and an accessible ΔG‡ barrier. Our computational results, which are in consonance with the kinetic parameters derived from lumped models, the results of isotopic labeling experiments and the reported HMF/FF molecular ratios, could be useful for modeling studies including on nonequilibrium kinetic effects that may render more information about product yields and the relevance of the various pathways.

New quantum assignments and analysis of high-resolution H212CO spectra in the range 3700–4450 cm-1

Four spectra of formaldehyde in natural isotopic abundance in the 3700–5200 cm-1 region were recorded at low temperature 160–166 K at Synchrotron SOLEIL for various pressures. Line positions and intensities were retrieved by non-linear least-squares curve-fitting procedures in the range 3700–4450 cm-1 and analyzed using ab initio based effective Hamiltonian and line intensities computed using new ab initio dipole moment surface. A new measured line list contains positions and intensities for 6177 features. Refined parameters of effective Hamiltonian were fitted to all assigned line positions with the RMS deviations of 0.001 cm-1. Updated line lists include intensity values based on ab initio variational calculations which were subsequently empirically optimized. Comparison of our theoretical simulation with previously available data as well as with high-resolution and low-resolution experimental spectra are reported.