Orbital Occupation Research Articles

Ultrafast magnetization and energy flow in the laser-induced dynamics of transition metal compounds

An electronic theory of the laser-induced ultrafast magnetization dynamics in transition-metal alloys is presented. A many-body model Hamiltonian is considered that incorporates the fundamental electronic hopping, local Coulomb interaction, and spin-orbit coupling (SOC) on the same footing. Exact time propagations are performed on a tetrahedral cluster, from which the time dependencies of the local spin moments, orbital occupations, and single-particle energies of homogeneous systems and binary alloys are obtained. The consequences of inhomogeneities in the laser absorption and in the SOC strengths are investigated giving emphasis to the nature of spin-density transfers between the alloy components. A local perspective on the optically induced spin transfer is proposed in terms of which two main steps emerge: a dominantly local optical excitation followed by hopping-driven spin-density transfers among the different alloy components. The conjoint action of the spin-orbit interactions at the origin of local spin flips and spin-to-orbital angular-momentum transfer and the interatomic hoppings responsible for charge, spin, and energy flows between different sublattices is demonstrated. Transient and steady-state dynamical regimes are identified that result in delays in the onset of the local demagnetizations and in ultrafast redistributions of the spin. The central role of electron delocalization and electronic hopping in the spin-density redistribution and demagnetization of the different alloy components is demonstrated.

A U(6) Boson Model for Deformed Nuclei

The Interacting Boson Model is one of the most famous group-theoretical nuclear models, which established the use of the U(6) symmetry in nuclei, built upon the s,d bosons, which derive by nucleon pairs. In this article, it is suggested that the symmetric pairs of the valence harmonic oscillator quanta can be used approximately as the s and d bosons of a new U(6) Boson Model, applicable in medium mass and heavy nuclei. The main consequence of this interpretation is that the number of bosons is the number of the pairs of the valence harmonic oscillator quanta, which occur from the occupation of the Shell Model orbitals by nucleons.

Large Orbital Magnetic Moment in VI3.

The existence of the V3+-ion orbital moment is an open issue of the nature of magnetism in the van der Waals ferromagnet VI3. The huge magnetocrystalline anisotropy in conjunction with the significantly reduced ordered magnetic moment compared to the spin-only value provides strong but indirect evidence of a large V orbital moment. We used the unique capability of X-ray magnetic circular dichroism to determine the orbital component of the total magnetic moment and provide a direct proof of an exceptionally sizable orbital moment of the V3+ ion in VI3. Our ligand field multiplet simulations of the XMCD spectra in synergy with the results of DFT calculations agree with the existence of two V sites with different orbital occupations and OM magnitudes in the ground state.

GW+EDMFT investigation of Pr1−xSrxNiO2 under pressure

Motivated by the recent experimental observation of a large pressure effect on ${T}_{c}$ in ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{NiO}}_{2}$, we study the electronic properties of this compound as a function of pressure for $x=0$ and 0.2 doping using self-consistent $GW+\mathrm{EDMFT}$. Our numerical results demonstrate a nontrivial interplay between chemical doping and physical pressure, and small but systematic changes in the orbital occupations, local level energies, and interaction parameters with increasing pressure. The proper treatment of correlation effects, beyond density functional theory, is shown to play an important role in revealing these trends. While the pressure-dependent changes in the electronic structure of the undoped compound suggest a more single-band-like behavior in the high-pressure regime, a qualitatively different behavior is found in the doped system. We also point out that the fluctuations in the orbital occupations and spin states are not consistent with a single-band picture, and that at least a two-band model is necessary to reproduce the full result. This multiorbital nature manifests itself most clearly in the doped compound.

One-electron self-interaction error and its relationship to geometry and higher orbital occupation.

Density Functional Theory (DFT) sees prominent use in computational chemistry and physics; however, problems due to the self-interaction error (SIE) pose additional challenges to obtaining qualitatively correct results. As an unphysical energy an electron exerts on itself, the SIE impacts most practical DFT calculations. We conduct an in-depth analysis of the one-electron SIE in which we replicate delocalization effects for simple geometries. We present a simple visualization of such effects, which may help in future qualitative analysis of the one-electron SIE. By increasing the number of nuclei in a linear arrangement, the SIE increases dramatically. We also show how molecular shape impacts the SIE. Two- and three-dimensional shapes show an even greater SIE stemming mainly from the exchange functional with some error compensation from the one-electron error, which we previously defined [D. R. Lonsdale and L. Goerigk, Phys. Chem. Chem. Phys. 22, 15805 (2020)]. Most tested geometries are affected by the functional error, while some suffer from the density error. For the latter, we establish a potential connection with electrons being unequally delocalized by the DFT methods. We also show how the SIE increases if electrons occupy higher-lying atomic orbitals; seemingly one-electron SIE free methods in a ground are no longer SIE free in excited states, which is an important insight for some popular, non-empirical density functional approximations (DFAs). We conclude that the erratic behavior of the SIE in even the simplest geometries shows that robust DFAs are needed. Our test systems can be used as a future benchmark or contribute toward DFT development.

The chemical reactivity and antimalarial investigation of crystal structure (2E)-3-(biphenyl-4-yl)-1-(4-chlorophenyl)prop-2-en-1-one and hydroxyphenyl, nitrophenyl substituted chalcone derivative molecules

In the present study, the chlorophenyl substituted chalcone derivative molecule ((2E)-3-(biphenyl-4-yl)-1-(4-chlorophenyl) prop-2-en-1-one (BCPO)) was synthesized and characterized by spectroscopic (FT-IR, FT-Raman and UV-Vis) techniques. In addition, the molecular structures of chlorophenyl, hydroxyphenyl, nitrophenyl substituted chalcone derivative ((2E)-3-(biphenyl-4-yl)-1-(4-chlorophenyl) prop-2-en-1-one (BCPO), (2E)-3-(biphenyl-4-yl)-1-(4- hydroxyphenyl) prop-2-en-1-one (BHPO) and (2E)-3-(biphenyl-4-yl)-1-(4-nitrophenyl) prop-2-en-1-one (BNPO)) molecules were optimized. The vibration frequencies were calculated and compared with experimental spectral data of BCPO molecule. The molecular orbital occupancies were computed using highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) analyses, and time-dependent density functional theory (TDDFT) applied to calculate Ultraviolet (UV) - Visible absorbance spectra using a solvated approach. The molecular reactivity chemical behaviour of the BCPO, BHPO and BNPO compounds with their electrostatic potential charge identifications, electrophilic, and nucleophilic individual atomic reactions were performed using molecular electrostatic potential (MEP) maps, Fukui functions, and dual descriptors studies. Non-linear optical properties, intermolecular energy transfer, bonding types, and stabilization energies were performed by natural bond orbital (NBO) analysis. The molecular stabilization and intermolecular interactions of BCPO molecule were performed using Hirshfield and 2D finger plot analysis. The antimalarial activities of BCPO, BHPO and BNPO molecules were obtained using molecular docking analysis.

Impact of first-row transition metals in (Ba,La)(Fe,TM)O3-δ on proton uptake and electronic conductivity

Oxides with mixed proton, oxygen vacancy, and hole conductivity are key functional materials for fuel and electrolyzer cells based on protonic ceramic electrolytes. Here, we explore the effect of partial B-site substitution of Ba0.95La0.05FeO3-δ with first-row transition metals, clarifying the impact on hydration and electronic conductivity. An anti-correlation between proton uptake and electronic conductivity is observed: Zn- doped compositions favor protonation and decrease electronic conductivity; the opposite holds for Co-containing samples. Cu- and Ni- doped materials deviate positively from this general trend. We ascribe this behavior to an interplay of Cu (Ni)-O bond covalency, charge transfer, and d orbital occupancy. Codoping with 10 mol% of late transition metals and 10 mol% of zinc strongly increases the proton uptake while yielding a reasonable electronic conductivity. In particular, Ba0.95La0.05Fe0.8(Co,Ni,Cu)0.1Zn0.1O3-δ samples show both high proton uptake and electronic conductivity, suggesting it as promising cathode material.

Achieving High-Temperature Multiferroism by Atomic Architecture

Materials with multiple order parameters, typically, in which ferroelectricity and magnetism are coupled, are illuminative for next-generation multifunctional electronics. However, searching for such single-phase multiferroics is challenging owing to antagonistic orbital occupancy and chemical bonding requirements for polarity and magnetism. Appropriate multiferroic candidates have been proposed, but their practical implementation is impeded by the low working temperature, weak coupling between ferroic orders, or antiparallel spin alignment in magnetic sublattices. Here, we report a family of single-phase multiferroic materials in which high-temperature magnetism and voltage-switchable ferroelectricity are coupled. Using pulsed laser deposition, we have fabricated single-crystalline thin films incorporating a uniformly percolated open-shell dn framework, which are composed of Fe cations with B-site occupancy and exhibit long-range spin ordering into the displacive ferroelectric PbTiO3 lattice, as demonstrated by atomically resolved chemical analysis. The tetragonal polar Pb(Ti1-x,Fex)O3 (PFT(x), x ≤ 0.10) family exhibits a switchable ferroelectric nature and magnetic interaction with a moderate coercive field of around 300 Oe at room temperature. Notably, the magnetic order even persists above 500 K, which is higher than already reported potential multiferroic candidates until now. Our strategy of merging a spin-ordered sublattice into inherent ferroelectrics via atomic occupancy engineering provides an available pathway for highly thermally stable multiferroic and spintronic applications.

On the atomistic origin of the polymorphism and the dielectric physical properties of beryllium oxide.

Polymorphic beryllium oxide has been theoretically investigated from first principles as regards orbital occupancies, chemical bonding, polarization, as well as dielectric properties. By means of Crystal-Orbital Bond Index (COBI) analysis, the important role of the 2p orbitals on beryllium has been elucidated, in particular in terms of the correlation between polarization and beryllium-atom displacement, including the impact of the latter on the covalency of the BeO bond. In addition, several structural possibilities for a Bex Mg1-x O solid solution have been investigated for a Be content between 6% and 22%; for those, dynamically stable structures have been found, displaying large polarization values, more covalent BeO bonds, and a tendency for tetrahedral Be coordination. The dynamically unstable structures, however, resemble rock-salt BeO in their local structural properties around the Be atom. High dielectric constants and band gaps indicating insulating behavior have been found for those.

Study of the N=32 and N=34 Shell Gap for Ti and V by the First High-Precision Multireflection Time-of-Flight Mass Measurements at BigRIPS-SLOWRI.

The atomic masses of ^{55}Sc, ^{56,58}Ti, and ^{56-59}V have been determined using the high-precision multireflection time-of-flight technique. The radioisotopes have been produced at RIKEN's Radioactive Isotope Beam Factory (RIBF) and delivered to the novel designed gas cell and multireflection system, which has been recently commissioned downstream of the ZeroDegree spectrometer following the BigRIPS separator. For ^{56,58}Ti and ^{56-59}V, the mass uncertainties have been reduced down to the order of 10keV, shedding new light on the N=34 shell effect in Ti and V isotopes by the first high-precision mass measurements of the critical species ^{58}Ti and ^{59}V. With the new precision achieved, we reveal the nonexistence of the N=34 empirical two-neutron shell gaps for Ti and V, and the enhanced energy gap above the occupied νp_{3/2} orbit is identified as a feature unique to Ca. We perform new MonteCarlo shell model calculations including the νd_{5/2} and νg_{9/2} orbits and compare the results with conventional shell model calculations, which exclude the νg_{9/2} and the νd_{5/2} orbits. The comparison indicates that the shell gap reduction in Ti is related to a partial occupation of the higher orbitals for the outer two valence neutrons at N=34.

Al-Pt intermetallic compounds: HAXPES study.

Intermetallic compounds in the Al-Pt system were systematically studied via hard X-ray photoelectron spectroscopy, focusing on the positions of Pt 4f and Al 2s core levels and valence band features. On one hand, with increasing Al content, the Pt 4f core levels shift towards higher binding energies (BE), revealing the influence of the atomic interactions (chemical bonding) on the electronic state of Pt. On the other hand, the charge transfer from Al to Pt increases with increasing Al content in Al-Pt compounds. These two facts cannot be combined using the standard "chemical shift" approach. Computational analysis reveals that higher negative effective charges of Pt atoms are accompanied by reduced occupancy of Pt 5d orbitals, leading to the limited availability of these electrons for the screening of the 4f core hole and this in turn explains the experimentally observed shift of 4f core levels to higher BE.

How does multi-reference computation change the catalysis chemistry? DFT and CASPT2 studies of the Cu-catalysed coupling reactions between aryl iodides and β-diketones.

The molecular mechanism of a Cu-catalysed coupling reaction was theoretically studied using density functional theory (DFT) and the complete active space self-consistent field method followed by the second-order perturbation theory (CASSCF/CASPT2) to investigate the effects of the strong electron correlation of the Cu centre on the reaction profile. Both DFT and CASSCF/CASPT2 calculations showed that the catalytic cycle proceeds via an oxidative addition (OA) reaction, followed by a reductive elimination (RE) reaction, where OA is the rate-determining step. Although the DFT-calculated activation energies of the OA and RE steps are highly dependent on the choice of functionals, the CASSCF/CASPT2 results are less affected by the choice of DFT-optimised geometries. Therefore, with a careful assessment based on the CASSCF/CASPT2 single-point energy evaluation, an optimal choice of the DFT geometry is of good qualitative use for energetics at the CASPT2 level of theory. Based on the changes in the electron populations of the 3d orbitals during the OA and RE steps, the characteristic features of the DFT-calculated electronic structure were qualitatively consistent with those calculated using the CASSCF method. Further electronic structure analysis by the natural orbital occupancy of the CASSCF wavefunction showed that the ground state is almost single-reference in this system and the strong electron correlation effect of the Cu centre can be dealt with using the MP2 or CCSD method, too. However, the slightly smaller occupation numbers of the 3dπ orbital in the course of reactions suggested that the electron correlation effect of the Cu(III) centre appears through the interaction between the 3dπ orbital and the C-I antibonding σ* orbital in the OA step, and between the 3dπ orbital and the Cu-C antibonding σ* orbital in the RE step.

An ab initio study on the stability of isolated phosphaalkene synthons.

Using ab initio methods and flexible basis sets, we examined the electronic, geometric, and thermodynamic stabilities of selected phosphaalkene synthons matching the (PCR2)- formula (R = H, CH3, C6H5, C6F5, and Mes). All isolated synthons considered were found to be electronically stable and susceptible to neither fragmentation nor isomerization processes. The structures corresponding to the most stable isomers of the studied phosphaalkene synthons contain a PC double-bond (whose presence was confirmed by natural bond orbital occupancies of σ(P-C) and π(P-C) approaching 2 electrons) and two R substituents connected to the carbon atom in either (PCR2)- (for R = H, CH3, C6H5, and Mes) or (PCF-R-R)- (for R = C6F5) manner. Vertical electron detachment energies (spanning the 0.924-3.118 eV range) characterizing the phosphaalkene synthons were predicted and discussed.

Synthesis, Spectral Investigation, DFT, Antibacterial, Antifungal and Molecular Docking Studies of Ni(II), Zn(II), Cd(II) Complexes of Tetradentate Schiff-Base Ligand

By refluxing 4-nitro-o-phenylenediamine and 5-nitro salicylaldehyde, a new Schiff base ligand was synthesized. By reacting the appropriate precursor with the tetradentate Schiff base ligand, three nitro-substituted nickel(II), zinc(II) and cadmium(II) complexes were synthesized. UV-Visible, FTIR and 1H NMR spectral investigations were used to characterize the ligand. Molar conductance, LC-MS, UV-visible and FTIR spectrum analysis were used to characterize the synthesized metal(II) complexes. The ligand and metal(II) complexes were also tested for antibacterial activity. DFT simulations were performed at the B3LYP/6-311G (d,p) and LanL2dz levels of theory were utilized to study the geometry of the Schiff base ligand and the metal(II) complexes. In addition, the molecular orbital occupancy of HOMO and LUMO, as well as the molecular electrostatic potential (MEP), were computed. Molecular docking investigation were conducted utilizing the active sites of the E. coli FabH-CoA complex (PDB ID: 1HNJ) receptor in order to detect the interactions between metal(II) complexes and define their likely binding locations.

Natural orbitals and two-particle correlators as tools for the analysis of effective exchange couplings in solids.

Using generalizations of spin-averaged natural orbitals and two-particle charge correlators for solids, we investigate the electronic structure of antiferromagnetic transition-metal oxides with a fully self-consistent, imaginary-time GW method. Our findings disagree with the Goodenough-Kanamori (GK) rules that are commonly used for the qualitative interpretation of such solids. First, we found a strong dependence of the natural orbital occupancies on momenta, contradicting GK assumptions. Second, along the momentum path, the character of natural orbitals changes. In particular, the contributions of oxygen 2s orbitals are important, which has not been considered in the GK rules. To analyze the influence of the electronic correlation on the values of effective exchange coupling constants, we use both natural orbitals and two-particle correlators and show that electronic screening modulates the degree of superexchange by stabilizing the charge-transfer contributions, which greatly affects these coupling constants. Finally, we give a set of predictions and recommendations regarding the use of density functional, Green's function, and wave-function methods for evaluating effective magnetic couplings in molecules and solids.

N,S coordination in Ni single-atom catalyst promoting CO2RR towards HCOOH.

Carbon-based single atom catalysts (SACs) are attracting extensive attention in the CO2 reduction reaction (CO2RR) due to their maximal atomic utilization, easily regulated active center and high catalytic activity, in which the coordination environment plays a crucial role in the intrinsic catalytic activity. Taking NiN4 as an example, this study reveals that the introduction of different numbers of S atoms into N coordination (Ni-NxS4-x (x = 1-4)) results in outstanding structural stability and catalytic activity. Owing to the additional orbitals around -1.60 eV and abundant Ni dxz, dyz, dx2, and dz2 orbital occupation after S substitution, N,S coordination can effectively facilitate the protonation of adsorbed intermediates and thus accelerate the overall CO2RR. The CO2RR mechanisms for CO and HCOOH generation via two-electron pathways are systematically elucidated on NiN4, NiN3S1 and NiN2S2. NiN2S2 yields HCOOH as the most favorable product with a limiting potential of -0.24 V, surpassing NiN4 (-1.14 V) and NiN3S1 (-0.50 V), which indicates that the different S-atom substitution of NiN4 has considerable influence on the CO2RR performance. This work highlights NiN2S2 as a high-performance CO2RR catalyst to produce HCOOH, and demonstrates that N,S coordination is an effective strategy to regulate the performance of atomically dispersed electrocatalysts.

Yttrium separation by phosphorylcarboxylic acid and the underlying tetrad effect along lanthanide unveiled from different microscopic interactions

Due to similar physical and chemical properties, separating and purifying rare earth elements is challenging. Considering the environmental issue, the design and synthesis of efficient and green extractants are significant for this purpose. To this end, the underlying complexation between rare earth and the extractant should be clarified, and the long-historically existing tetrad effect along with the lanthanide family from La to Lu due to the different 4f orbital occupations should be figured out. Thus, within this study, taking our newly experimentally synthesized extractant, phosphorylcarboxylic acid, as an example and utilizing accurate quantum mechanical calculation, we comprehensively investigated the complexation behavior between rare earth and the extractant via the quantum theory of atoms in molecules (QTAIM), Mayer bond order (MBO), molecular orbital (MO) energy level, natural bond orbital (NBO), charge decomposition analysis (CDA), electron localization function (ELF) and extended transition state-natural orbitals for chemical valence (ETS-NOCV). It has been found that yttrium can be separated from the lanthanide series by the phosphorylcarboxylic acid, attributed to the poor ability of Y3+ to accept electrons and the weak orbital interactions compared to other rare earth cations. This paper also reveals the tetrad effect caused by the different occupations of 4f orbital electrons, providing a theoretical approach to comprehending the diverse extraction behaviors in the rare earth extraction process.

Adjusting the 3d Orbital Occupation of Ti in Ti3C2 MXene via Nitrogen Doping to Boost Oxygen Electrode Reactions in Li–O2 Battery

Rationally designing efficient catalysts is the key to promote the kinetics of oxygen electrode reactions in lithium-oxygen (Li-O2 ) battery. Herein, nitrogen-doped Ti3 C2 MXene prepared via hydrothermal method (N-Ti3 C2 (H)) is studied as the efficient Li-O2 battery catalyst. The nitrogen doping increases the disorder degree of N-Ti3 C2 (H) and provides abundant active sites, which is conducive to the uniform formation and decomposition of discharge product Li2 O2 . Besides, density functional theory calculations confirm that the introduction of nitrogen can effectively modulate the 3d orbital occupation of Ti in N-Ti3 C2 (H), promote the electron exchange between Ti 3d orbital and O 2p orbital, and accelerate oxygen electrode reactions. Specifically, the N-Ti3 C2 (H) based Li-O2 battery delivers large discharge capacity (11679.8mAh g-1 ) and extended stability (372 cycles). This work provides a valuable strategy for regulating 3d orbital occupancy of transition metal in MXene to improve the catalytic activity of oxygen electrode reactions in Li-O2 battery.

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC+/0/.

A combination of high-level ab initio calculations and anion photoelectron detachment (PD) measurements is reported for the UC, UC-, and UC+ molecules. To better compare the theoretical values with the experimental photoelectron spectrum (PES), a value of 1.493 eV for the adiabatic electron affinity (AEA) of UC was calculated at the Feller-Peterson-Dixon (FPD) level. The lowest vertical detachment energy (VDE) is predicted to be 1.500 eV compared to the experimental value of 1.487 ± 0.035 eV. A shoulder to lower energy in the experimental PD spectrum with the 355 nm laser can be assigned to a combination of low-lying excited states of UC- and excited vibrational states. The VDEs calculated for the low-lying excited electronic states of UC at the SO-CASPT2 level are consistent with the observed additional electron binding energies at 1.990, 2.112, 2.316, and 3.760 eV. Potential energy curves for the Ω states and the associated spectroscopic properties are also reported. Compared to UN and UN+, the bond dissociation energy (BDE) of UC (411.3 kJ/mol) is predicted to be considerably lower. The natural bond orbitals (NBO) calculations show that the UC0/+/- molecules have a bond order of 2.5 with their ground-state configuration arising from changes in the oxidation state of the U atom in terms of the 7s orbital occupation: UC (5f27s1), UC- (5f27s2), and UC+ (5f27s0). The behavior of the UN and UC sequence of molecules and anions differs from the corresponding sequences for UO and UF.

Charge-orbital Ordering, Magnetic State, and Exchange Couplings in Quasi-One-Dimensional Vanadate V6O13

Charge and orbital ordering, magnetic state, and exchange couplings in quasi-one-dimensional vanadate V6O13, a potential cathode material for Li-ion batteries, are investigated using the density functional theory with Coulomb interaction correction method (DFT + U). While the difference between {{t}_{{2g}}} orbital occupancies of V4+ (with a nominal 3{{d}^{1}} electronic configuration) and V5+ ions is large and gives direct evidence for charge and orbital ordering, the screening is so effective that the total 3d charge disproportionation is rather small. Our results show that the occupied {{t}_{{2g}}} states of V4+ ions in the single V–V layer form a spin-singlet molecular orbital, while the rest half of V4+ ions in the structurally distinct double V–V layers order antiferromagnetically in the low-temperature insulating phase of V6O13. We conclude that the metal-insulator transition and low-temperature magnetic properties of V6O13 involve the spin-Peierls transition assisted by orbital ordering and concomitant distortions of the crystal structure.