Ground-state Structure Research Articles

Phosphine versus Carbene Metal Interactions: Bond Energies.

A variety of different ground-state structures of carbene and phosphine groups 1 and 2 cationic, group 11 cationic, and group 10 neutral complexes were studied using density functional theory (DFT) and correlated molecular orbital theory (CCSD(T)) methods. Geometries of complexes with phosphines were studied and compared to available experimental data. Among the three analyzed phosphine ligands, PH3, PMe3, and PPh3, PH3 was found to have noticeably smaller ligand binding energies (LBEs, ΔH298 K). PPh3 has the greatest LBEs with group 2 dications. The difference in LBEs for PMe3 and PPh3 in complexes with group 1 monocations and transition-metal (TM) complexes was significantly less pronounced. The stability and reactivity of phosphine complexes were analyzed and compared with those of previously studied N-heterocyclic carbenes (NHC). PH3 has smaller LBEs compared to NHC carbenes. The lower LBEs correlate with the hardness for M(11)+ complexes and correlate with both the hardness and ionic radii for the M(1)+ and M(2)2+ complexes. The presence of additional PH3 substituents on the metal center makes the LBE smaller compared to their unsubstituted or less substituted analogs. The presence of NH3 in a structure causes a smaller effect on binding, and, except for carbene-PtNH3, an increase in LBE was observed. Composite-correlated molecular orbital theory (G3MP2) was used to predict the LBE of various Lewis acidic ligands with PH3 and NHCs to contrast their binding behavior. Binding either phosphine or carbene to metal diamine complexes caused ligand exchange and transfer of NH3 to an outer coordination sphere.

Theoretical Investigation on Water-Free, Water- and Self-Assisted H-Abstraction Reactions from Dimethylamine by Hydroxy Radicals.

Accurate branching ratios of the H-abstraction reactions from dimethylamine (DMA) by OH radicals are important in understanding the atmospheric fate of DMA. In this work, the reaction kinetics of the water-free, water-assisted, and self-assisted H-abstraction reactions between DMA and OH radicals are accurately determined using the multipath canonical variational theory with the small-curvature tunneling correction, to explore the catalytic effects of the reactant (DMA) and product (water). To choose a suitable method that well describes the current reaction systems, various combinations with seven DFT methods and six basis sets are first evaluated, and the M08-HX/ma-TZVP method is identified as the most appropriate, with a mean unsigned deviation of 0.9 kcal mol-1 against the gold-standard CCSD(T)/CBS(T-Q) method. Based on the determined potential energy surfaces with the considerations of ground-state structures and specific-reaction parameters of zero-point energies, rate constants and branching ratios are calculated in a wide temperature range. The calculations show that the participation of water and DMA can lead to three-body complexes with a lower energy and influence the energy barriers, but neither of them shows the catalytic effect on the H-abstraction reactions in terms of kinetics. Additionally, the branching ratio analysis demonstrates that the product distribution is significantly altered in the presence of DMA and water.

Novel ground state structures of N-doped LuH3

Ab-initio crystal structure searches have played a pivotal role in recent discoveries of high-Tc hydride superconductors under high pressure. Using evolutionary crystal searches, we predict novel ground state structures of N-doped LuH3 at ambient conditions. We find an insulating ground state structure for LuN0.125H2.875 (∼1.0 wt.% N), contrary to earlier studies where assumed structures were all metallic. This insulating behavior of ground state was found to persist up to ∼45 GPa. However our crystal structure searches revealed a metallic state for an H-deficient variant of LuN0.125H2.875. We study bonding characteristics of important structures by calculating electronic density of states, electronic-localization functions and Bader charges. Our Bader charge analysis shows that insulators have both H+ and H− ions whereas metals have only H− ions. We find that H+ ions are bonded to N atoms via a very short covalent bond. Thus we identify a clear relationship between formation of N–H bonds and insulating behavior of materials. Besides this, we perform crystal structure searches for three more compositions with higher N-content (>1.0 wt.%). Analysis of electronic properties shows that the ground states of these compositions are insulator.

Investigating quantum coherence of N-methylpyrrole through vibrational spectroscopy and potential energy: A theoretical study

Quantum chemical calculations are utilized to analyze the potential causes of N-methylpyrrole oscillations, focusing on vibration spectra and potential energy curves. Optimization of the ground state, ionic state and 3s state structure reveal mostly sp2 hybridization. An analysis of the 3s state vibration spectrum and adiabatic binding energy indicate that changes in dihedral angles D2,3,4,1 and plane angle A3,2,1 are potential factors contributing to molecular oscillations. The role of vertical binding energy and adiabatic binding energy in the oscillation process are also discussed, shedding light on the possible dynamic processes of N-methylpyrrole.

A computational investigation of XnK(X = Mn, Fe, co; n = 1–8) clusters by density functional theory

The properties of XnK(X = Mn, Fe, Co; n = 1–8) clusters have been systematically investigated using quantum calculations of LANL2DZ basis sets at the PBE1PBE level. By optimizing different structural isomers, we determined the ground state structure of XnK clusters, which tends to be compact as the cluster size increases. In order to study the stability of clusters, the average binding energies, dissociation energies and second-order difference of total energies of XnK clusters are calculated. The results show that the stability of FenK clusters is comparable to that of ConK clusters, and both are higher than that of MnnK clusters. Finally, the chemical activity and magnetic properties of the clusters are discussed. The dissociation energies, second-order difference of total energies, HOMO-LUMO energy gaps, and magnetic moments of the ground-state clusters show an irregular oscillatory behavior with atomic number. Fundamental insights obtained in this study can be useful in the design of Mn-K/Fe-K/Co-K catalysts.

Investigating electron-induced dissociation dynamics in the organometallic precursor Fe(CO)5: a nonadiabatic molecular dynamics approach

This research employs excited states molecular dynamics simulations to explore the electron-induced dissociation behavior of Fe(CO)5 molecules, with the specific focus on electronic excitation. The study initiates with the detailed analysis of the molecule’s stable ground state structure. Subsequent simulations reveal distinctive dissociation patterns in various bonds, particularly noting the rapid dissociation of bonds between Fe and C1, Fe and C2, while those with Fe and C3 oscillate without complete dissociation. Emphasizing the influence of the transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital on reactivity, the investigation sheds light on the charge transfer phenomenon during dissociation through Bader analysis. Insights into transitions between excited and ground states are derived from the time evolution of the Kohn–Sham orbital. This study significantly contributes to understanding intricate dissociation mechanisms under electronic excitation, especially in molecules like Fe(CO)5 characterized by complex chemical bonds. Beyond theoretical exploration, the research holds practical significance for applications in nanomaterials, such as focused electron beam-induced deposition and the fabrication of nanoscale structures, enriching our comprehension of electronic-excitation-induced dissociation and advancing both theoretical understanding and practical applications in this field.

Half metallic ferromagnetic and transport behavior of rare earth based CdGd2(S/Se)4 spinels

Spinel chalcogen compounds have garnered significant interest in recent ages because of their promising potential in optoelectronic and thermoelectric device applications. Here, we undertake an inclusive analysis of the structural, mechanical, electronic, magnetic, optical, and transport response of CdGd2(S/Se)4 utilizing WIEN2k code based on DFT. The determination of the crystal structure's ground state and the material's thermodynamic stability is investigated through energy vs. volume plots and ∆Hf calculation. Our analysis, including Poisson (v) and Pugh (B/G) ratios, reveals the ductile nature of the studied composition. Band gap assessments are conducted using the TB-mBJ approach, revealing the semiconducting nature of investigated compounds with direct band characteristics. Specifically, calculated band gap values are 2.2 for CdGd2S4 and 1.8 eV for CdGd2Se4. Additionally, analysis of optical properties and transport response underscores the perspective of these compositions for diverse optoelectronic and thermoelectric devices.

Adsorption of dihalogen molecules X2 (X = F, Cl, Br and I) on the Fe/W(110) substrate

We report on spin-polarized density-functional theory study of adsorption of dihalogen molecules X2 (X = F, Cl, Br and I) on the Fe/W(110) substrate, i.e., X2/Fe/W(110) systems. We considered different molecular orientations and adsorption sites of the halogens and obtained their corresponding ground-state structures. We obtained initial molecular orientation (IMO) and initial adsorption site (IAS), i.e., IMO-IAS combinations that give the minimum energy configurations for each of the X2/Fe/W(110) systems. Our results shows that all the molecules studied in this work are chemisorbed on the Fe surface. Also, the halogen atoms may be adsorbed dissociatively on the hollow sites in such a way that an X2 separates into two X atoms with each of the atoms located at two nearby hollow sites. Similarly, we found IMO-IAS combinations which resulted in a non-dissociative adsorption. In the latter, the pre-relaxed IMO-IAS is maintained even after the structural relaxation. The most stable configuration for the X2 dihalogen molecule in this case is either the top or bridge site while the halogen is in perpendicular orientation to the Fe surface. We conclude therefore that, the final relaxed configurations of the X2 halogen depends on the IMO through which is deposited on the Fe/W(110) substrate. The trend in the adsorption energy EA for the most stable configurations for the dissociative adsorption is EA (F) > EA (Cl) > EA (Br) > EA (I). The trend of EA for non-dissociative adsorption is similar to that of dissociative adsorption, however, the latter is the more energetically favorable. Electronic structure calculations show hybridization between the p and d orbitals of X and Fe atoms respectively. Furthermore, we have found antiferromagnetic coupling between the interfacial W atoms and the Fe overlayer atoms while ferromagnetic coupling is found between the halogens and the Fe atoms. Our work represents a detailed study of adsorption properties of highly reactive halogens in contact with the Fe/W(100) surface.

Going for Gold(-Standard): Attaining Coupled Cluster Accuracy in Oxide-Supported Nanoclusters.

The structure of oxide-supported metal nanoclusters plays an essential role in their sharply enhanced catalytic activity over that of bulk metals. Simulations provide the atomic-scale resolution needed to understand these systems. However, the sensitive mix of metal-metal and metal-support interactions, which govern their structure, puts stringent requirements on the method used, requiring calculations beyond standard density functional theory (DFT). The method of choice is coupled cluster theory [specifically CCSD(T)], but its computational cost has so far prevented its application to these systems. In this work, we showcase two approaches to make CCSD(T) accuracy readily achievable in oxide-supported nanoclusters. First, we leverage the SKZCAM protocol to provide the first benchmarks of oxide-supported nanoclusters, revealing that it is specifically metal-metal interactions that are challenging to capture with DFT. Second, we propose a CCSD(T) correction (ΔCC) to the metal-metal interaction errors in DFT, reaching accuracy comparable to that of the SKZCAM protocol at significantly lower cost. This approach forges a path toward studying larger systems at reliable accuracy, which we highlight by identifying a ground-state structure in agreement with experiments for Au20 on MgO, a challenging system where DFT models have yielded conflicting predictions.

The ground-state structures and spectra of neutral, anionic and cationic copper clusters

The structures and spectra of Cunb (n = 3–16; b = 0, ±1) clusters have been researched by means of density functional theory (DFT) coupled with CALYPSO structure prediction method. It is found that the growth of Cun (n = 9–16) clusters shows a clear regularity. Based on the global minimum structure of the Cun cluster, the UV spectra have been predicted and are in good agreement with the available experimental results. The most stable structures of anionic copper clusters have been identified by comparing experimental and theoretical photoelectron spectra (PES). The infrared (IR) and Raman spectra of cationic copper clusters have been simulated and the calculated IR spectra of Cun+ -Arm (n = 3–10) complexes are in accord with experimental spectra. The Ar atoms adsorbed to small Cun+ cluster have partly influence on the IR spectrum of the host cluster. The Cu6, Cu8 and Cu3+ clusters can be regard as three magic clusters.

Exploring FeMnVAl Heusler Alloy: Physical, Mechanical, and Magnetic Properties

The structural, mechanical, electronic, and magnetic properties of equiatomic quaternary Heusler alloy FeMnVAl have been investigated using first-principles approach. This alloy shows ferromagnetic ground state structure with chemical stability indicating compound fulfills the criteria for synthesizing experimentally. The calculated values of Pugh’s index and Poisson’s ratio confirmed ductile nature of FeMnVAl. The investigation of band structure and density of states validates the behaviour of half[1]metallic ferromagnetism (HMFs), which follow the Slater-Pauling rule Mt = Zt - 24 and have a magnetic moment value of around 1 μB/f.u. Its features also allow for potential applications in the realm of spintronics devices and optoelectronics.

NoRA: A Tensor Network Ansatz for Volume-Law Entangled Equilibrium States of Highly Connected Hamiltonians

Motivated by the ground state structure of quantum models with all-to-all interactions such as mean-field quantum spin glass models and the Sachdev-Ye-Kitaev (SYK) model, we propose a tensor network architecture which can accomodate volume law entanglement and a large ground state degeneracy. We call this architecture the non-local renormalization ansatz (NoRA) because it can be viewed as a generalization of MERA, DMERA, and branching MERA networks with the constraints of spatial locality removed. We argue that the architecture is potentially expressive enough to capture the entanglement and complexity of the ground space of the SYK model, thus making it a suitable variational ansatz, but we leave a detailed study of SYK to future work. We further explore the architecture in the special case in which the tensors are random Clifford gates. Here the architecture can be viewed as the encoding map of a random stabilizer code. We introduce a family of codes inspired by the SYK model which can be chosen to have constant rate and linear distance at the cost of some high weight stabilizers. We also comment on potential similarities between this code family and the approximate code formed from the SYK ground space.

Investigation of Isolated IrF5 -, IrF6 - Anions and M[IrF6] (M=Na, K, Rb, Cs) Ion Pairs by Matrix-Isolation Spectroscopy and Relativistic Quantum-Chemical Calculations.

The molecular IrF5 -, IrF6 - anions and M[IrF6] (M=Na, K, Rb, Cs) ion pairs were prepared by co-deposition of laser-ablated alkali metal fluorides MF with IrF6 and isolated in solid neon or argon matrices under cryogenic conditions. The free anions were obtained as well by co-deposition of IrF6 with laser-ablated metals (Ir or Pt) as electron sources. The products were characterized in a combined analysis of matrix IR spectroscopy and electronic structure calculations using two-component quasi-relativistic DFT methods accounting for spin-orbit coupling (SOC) effects as well as multi-reference configuration-interaction (MRCI) approaches with SOC. Inclusion of SOC is crucial in the prediction of spectra and properties of IrF6 - and its alkali-metal ion pairs. The observed IR bands and the computations show that the IrF6 - anion adopts an Oh structure in a nondegenerate ground state stabilized by SOC effects, and not a distorted D4h structure in a triplet ground state as suggested by scalar-relativistic calculations. The corresponding "closed-shell" M[IrF6] ion pairs with C3v symmetry are stabilized by coordination of an alkali metal ion to three F atoms, and their structural change in the series from M=Na to Cs was proven spectroscopically. There is no evidence for the formation of IrF7, IrF7 - or M[IrF7] (M=Na, K, Rb, Cs) ion pairs in our experiments.

Spin–orbit-coupled Bose gas with Rydberg interactions confined in a two-dimensional optical lattice

We consider the ground state of Rydberg-dressed Bose gas with spin–orbit coupling and confined in a two-dimensional optical lattice. The effects of system’s parameters, especially the nonlocal Rydberg interaction and spin–orbit coupling, on the ground-state structure of such a system are explored in full parameter space. It is found that in the absence of spin–orbit coupling, the ground-state structure of the system changes from the initial optical lattice structure to a two-dimensional periodic one with the cell size decreasing with the strength of Rydberg interaction. In the presence of spin–orbit coupling, both the phase and the internal structure of unit cell show strong dependence on the strength of spin–orbit coupling. Finally, the strong interacting gas is also considered.

Impact of N-Glycosylation on Protein Structure and Dynamics Linked to Enzymatic C-H Activation in the M. oryzae Lipoxygenase.

Lipoxygenases (LOXs) from pathogenic fungi are potential therapeutic targets for defense against plant and select human diseases. In contrast to the canonical LOXs in plants and animals, fungal LOXs are unique in having appended N-linked glycans. Such important post-translational modifications (PTMs) endow proteins with altered structure, stability, and/or function. In this study, we present the structural and functional outcomes of removing or altering these surface carbohydrates on the LOX from the devastating rice blast fungus, M. oryzae, MoLOX. Alteration of the PTMs did notinfluence the active site enzyme-substrate ground state structures as visualized by electron-nuclear double resonance (ENDOR) spectroscopy. However, removal of the eight N-linked glycans by asparagine-to-glutamine mutagenesis nonetheless led to a change in substrate selectivity and an elevated activation energy for the reaction with substrate linoleic acid, as determined by kinetic measurements. Comparative hydrogen-deuterium exchange mass spectrometry (HDX-MS) analysis of wild-type and Asn-to-Gln MoLOX variants revealed a regionally defined impact on the dynamics of the arched helix that covers the active site. Guided by these HDX results, a single glycan sequon knockout was generated at position 72, and its comparative substrate selectivity from kinetics nearly matched that of the Asn-to-Gln variant. The cumulative data from model glyco-enzyme MoLOX showcase how the presence, alteration, or removal of even a single N-linked glycan can influence the structural integrity and dynamics of the protein that are linked to an enzyme's catalytic proficiency, while indicating that extensive glycosylation protects the enzyme during pathogenesis by protecting it from protease degradation.

Complexity of Supersymmetric Systems and the Cohomology Problem

We consider the complexity of the local Hamiltonian problem in the context of fermionic Hamiltonians with N=2 supersymmetry and show that the problem remains QMA-complete. Our main motivation for studying this is the well-known fact that the ground state energy of a supersymmetric system is exactly zero if and only if a certain cohomology group is nontrivial. This opens the door to bringing the tools of Hamiltonian complexity to study the computational complexity of a large number of algorithmic problems that arise in homological algebra, including problems in algebraic topology, algebraic geometry, and group theory. We take the first steps in this direction by introducing the k-local Cohomology problem and showing that it is QMA1-hard and, for a large class of instances, is contained in QMA. We then consider the complexity of estimating normalized Betti numbers and show that this problem is hard for the quantum complexity class DQC1, and for a large class of instances is contained in BQP. In light of these results, we argue that it is natural to frame many of these homological problems in terms of finding ground states of supersymmetric fermionic systems. As an illustration of this perspective we discuss in some detail the model of Fendley, Schoutens, and de Boer consisting of hard-core fermions on a graph, whose ground state structure encodes l-dimensional holes in the independence complex of the graph. This offers a new perspective on existing quantum algorithms for topological data analysis and suggests new ones.

9-Borafluoren-9-yl and diphenylboron tetracoordinate complexes of 8-quinolinolato ligands with heavy-atoms substituents: Synthesis, fluorescence and application in OLED devices

This work describes the synthesis and characterisation of new tetrahedral boron complexes, incorporating bromine- or iodine-substituted 8-quinolinolato chelate chromophores connected to 9-borafluoren-9-yl or diphenylboron orthogonal fragments. The molecular features and photophysical properties of these complexes are analysed in both solution and solid state. Steady-state photophysical studies reveal photoluminescence quantum yields (Φf) ranging from 0.02 to 0.15 and prompt fluorescence (PF) lifetimes (τf) between 2 and 16 ns. Time-resolved photophysical experiments show the presence of delayed fluorescence (DF) and phosphorescence at both 77 K and room temperature. The DF intensity increases with a rise in temperature. This variation is ascribed to an enhancement in the intersystem crossing (ISC) process promoted by the bromine or iodine heavy-atom effect. Investigations into the dependence of DF intensity relative to the excitation dose indicate emissions stemming either from Triplet-Triplet Annihilation (TTA), Thermally Activated Delayed Fluorescence (TADF), or a combination of these competing mechanisms. The effect is related to the size and number of heavy-atom substituents in each boron complex. A study of the DF emission intensity as a function of the excitation dose reveals that diiodo-substituted 8-quinolinolato boron complexes, whether rigid or flexible, display TADF emission. Rigid 5,7-dibromo- and 5-chloro-7-iodo-substituted 8-quinolinolato complexes exhibit a combined TADF-TTA mechanism, whereas the other complexes predominantly demonstrate pure TTA emission. DFT and TDDFT calculations showed that the ground state structures reproduced the experimental geometries and only small increases in bond lengths were observed in the excited state geometries. The low energy absorption bands displayed mainly intra-ligand π→π* (8-quinolinato) character. The fluorescence emission energies were well reproduced, while the singlet-triplet energy gaps were relatively high and spin-orbit coupling was relevant for complexes with heavy-atoms. Ultimately, organic light-emitting diodes (OLEDs) are fabricated using the most luminescent boron complexes. The best OLED is obtained when using complex 3a, which displays green electroluminescence (EL) (λEL = 502 nm) with maximum external quantum efficiency (EQEmax) of 2.5% and maximum luminance (Lmax) of 2200 cd m−2.

Electronic structure of double perovskite SrTi0.5Co0.5O3: order, disorder, and vacancy effects

In this study, we investigate the electronic structure of the ordered/disordered double perovskite SrTi0.5Co0.5O3 (STCO) using density functional theory (DFT) and the full-potential linearized augmented plane wave method. Detailed structural and magnetic stability analysis revealed that Sr2TiCoO6 crystallizes in the tetragonal I4/m space group, in which Co4+ and Ti4+ ions are distributed in an alternating arrangement along three directions. Notably, Sr2TiCoO6 exhibits a half-metallic property and exhibits ferromagnetic (FM) behavior, originating from the Co4+-O2--Ti4+ bonds and the high spin state of cobalt. Additionally, a chemical/magnetic stability analysis was carried out to identify the ground state structure in disordered STCO. The investigation identified a two-dimensional-like configuration (referred to as STC5FM) characterized by ferromagnetic order. This particular arrangement represents the most chemically stable layered configuration, featuring a maximal occurrence of Co–O–Co chains. Thus, Co4+ ions exhibit an intermediate spin state following Goodenough-Kanamori-Anderson rules of ferromagnetic mechanism. Interestingly, this structure also displays ferromagnetism at room temperature, accompanying with semiconductor properties. The study also explored the impact of oxygen vacancies. Remarkably, the ferromagnetic attributes remain robust even in the presence of oxygen vacancies. Moreover, a transition from semiconductor to metal behavior becomes evident under these conditions.

Machine Learning-Accelerated First-Principles Study of Atomic Configuration and Ionic Diffusion in Li10GeP2S12 Solid Electrolyte.

The solid electrolyte Li10GeP2S12 (LGPS) plays a crucial role in the development of all-solid-state batteries and has been widely studied both experimentally and theoretically. The properties of solid electrolytes, such as thermodynamic stability, conductivity, band gap, and more, are closely related to their ground-state structures. However, the presence of site-disordered co-occupancy of Ge/P and defective fractional occupancy of lithium ions results in an exceptionally large number of possible atomic configurations (structures). Currently, the electrostatic energy criterion is widely used to screen favorable candidates and reduce computational costs in first-principles calculations. In this study, we employ the machine learning- and active-learning-based LAsou method, in combination with first-principles calculations, to efficiently predict the most stable configuration of LGPS as reported in the literature. Then, we investigate the diffusion properties of Li ions within the temperature range of 500-900 K using ab initio molecular dynamics. The results demonstrate that the atomic configurations with different skeletons and Li ion distributions significantly affect the Li ions' diffusion. Moreover, the results also suggest that the LAsou method is valuable for refining experimental crystal structures, accelerating theoretical calculations, and facilitating the design of new solid electrolyte materials in the future.

Structural mode coupling in perovskite oxides using hypothesis-driven active learning

Finding the ground-state structure with minimum energy is paramount to designing any material. In ABO3-type perovskite oxides with Pnma symmetry, the lowest energy phase is driven by an inherent trilinear coupling between the two primary order parameters such as rotation and tilt with antiferroelectric displacement of the A-site cations as established via hybrid improper ferroelectric mechanism. Conventionally, finding the relevant mode coupling driving phase transition requires performing first-principles calculations which is computationally time-consuming as well as expensive. It involves following an intuitive iterative hit and trial method of (a) adding two or multiple mode vectors, followed by (b) evaluating which combination would lead to the ground-state energy. In this study, we show how a hypothesis-driven active learning framework can identify suitable mode couplings within the Landau free energy expansion with minimal information on amplitudes of modes for a series of double perovskite oxides with A-site layered, columnar and rocksalt ordering. This scheme is expected to be applicable universally for understanding atomistic mechanisms derived from various structural mode couplings behind functionalities, for e.g. polarization, magnetization and metal–insulator transitions.