Low-energy States Research Articles

Arrangement of Azidomethyl Group in Lupinine Azide: Structural and Spectroscopic Properties

Quinolizidine derivatives are an important class of substances that are used in the pharmaceutical industry. In previous studies, the synthesis of these substances is carried out using lupinine azide (IUPAC: 1-(azidomethyl)octahydro-2H-quinolizine), which is often used to obtain new biologically active compounds. In this regard, its structural characterization is critically important. In this work, the conformational diversity of the molecular structure of this compound has been studied. It is shown that the structure with the axial position of the methyl azide group contains a number of low-energy conformer states with energies higher than the ground state by 0.15–0.60 kcal/mol. Such structural ambiguity should manifest itself in the chemical reactions and biological activity of lupinine azide. The spectroscopic properties of the conformers were studied by modeling chemical shifts for carbon and hydrogen atoms, as well as by simulating IR absorption spectra. An analysis of the most specific spectroscopic features of all of the conformers was carried out. Based on the correlation of the theoretical results and the experimental spectroscopic data, a conclusion was made for the first time regarding the most probable conformational states in the solution.

Optical Properties of Phenylthiolate-Capped CdS Nanoparticles.

Using many-body perturbation theory, we study the optical properties of phenylthiolate-capped cadmium sulfide nanoparticles to understand the origin of the experimentally observed blue shift in those properties with decreasing particle size. We show that the absorption spectra predicted by many-body perturbation theory agree well with the experimentally measured spectra. The results of our calculations demonstrate that all low-energy excited states correspond to a mixture of two fundamental types of excitations: intraligand and ligand-to-metal charge-transfer excitations. We find that for each excited state, the intraligand excitation contribution is dominant and that bright excited states, corresponding to the clear peaks in the absorption spectra, have a larger ligand-to-metal charge-transfer contribution. There are no low-energy bulk-like excitons, excited states for which both the hole and the excited electron components are predominantly delocalized over the inorganic core of the particles. Phenylthiolate-capped cadmium sulfide nanoparticles appear not to behave like the textbook cartoon picture of quantum dots. We speculate that the observed blue shift is the result of a combination of a Stark-like shift of the intraligand contribution, modulated by a change in the charge of the inorganic core and the confinement of the excited electron component of the ligand-to-metal charge-transfer contribution.

Surface Interactive Assembly of Ruthenium Based Janus Bimetallic Nanoparticles With Active Dual‐Function Sites for Efficient Use in CO2 Utilization

AbstractNoble bimetallic nanoparticles (NPs) are nowadays essential in various applications, like CO2 utilization by dry reforming of methane (DRM), due to their unique and potential properties. A synthesis method for Ru based Janus‐structured NPs is presented via surface interactive assembly of deposited Ru and emerged Ni species from carefully tailored perovskite oxide support. As noble‐metals typically result in the alloy, an exclusive formation mechanism is introduced by utilizing Ru energetically favorable for the Janus phase by lower ground state energy from interactions between the strongly embedded cluster and perovskite surface. Consequently, noticeable Janus NPs, controllable in size and composition with active configuration by dual‐function sites and interface strains, are well‐produced with high distribution. DRM performance highly exceeds conventional Ru over 5 times in TOFs for both CO2 and CH4 with improved stability maintaining H2/CO for 100 h without sintering at harsh reaction conditions, which comprehensively exhibits distinct advantages over recent works. Fundamental studies indicate combined electronic d‐band structures proving distinctive CO2 dissociation and CH4 activation, involving efficient dehydrogenation and CO production via surface oxygenation, considerably suppresses coking. This approach presents a potential avenue to surmount constraints on designing bimetallic NPs in any structured oxide systems for effective materials in various low carbon relevant industries.

Photophysical and Chiroptical Properties of Pyrazino-Phenanthroline-Helicene Derivative and its Rhenium(I) Complex.

A novel coordination motif comprising [4]helicene fused with pyrazino-phenanthroline (H4PP) has been synthesized and reacted with ReCl(CO)5 to yield its rhenium(I) complex (Re-H4PP). Absorption and emission spectroscopic analysis conducted in dichloromethane and 2-methyltetrahydrofuran reveals that combining pyrazino-phenanthroline with helicene visibly affects the photophysical attributes of both the resulting ligand and its Re(I) complex as compared to their non-helicene analogues, and even more importantly leads to relatively high photoluminescence quantum yield values, especially in the case of H4PP (29%). Chiroptical studies through electronic circular dichroism and circularly polarized luminescence performed on enantiomerically enriched samples of Re-H4PP show the chiral nature of low-energy excited states affording notable glum values that amplify at cryogenic temperatures. Insights into experimental results are provided via first-principles quantum-chemical calculations showing important role of intra-ligand charge-transfer (ILCT) and metal-to-ligand (MLCT) states in determining photophysical features of these systems.

Effect of A-DNA and B-DNA Conformation on the Interplay between Local Excitations and Charge-Transfer States in the Ultrafast Decay of Guanine-Cytosine Stacked Dimers: A Quantum Dynamical Investigation.

We here simulate in the gas phase the population dynamics of guanine/cytosine (GC) and cytosine/guanine (CG) stacked dimers in B-DNA and A-DNA arrangement, following excitation in the lowest-energy band, and considering the four lowest-energy ππ* bright excited states, the three lowest-energy nπ* states, and the G → C charge-transfer (CT) state. We resort to a generalized Linear Vibronic Coupling (LVC) model parametrized with time-dependent density functional theory (TD-DFT) computations, exploiting a fragment-based diabatization and we run nonadiabatic quantum dynamical simulations with the multilayer version of the Multiconfigurational Time-Dependent Hartree (ML-MCTDH) approach. G → C CT results in a major decay process for GC in B-DNA but less in A-DNA arrangement, where also the population transfer to the lowest-energy excited state localized on C is an important intermonomer process. In CG arrangements, mostly intramonomeric decays take place. We simulate the dynamics of several other GC structures whose arrangement is intermediate between B-DNA and A-DNA, obtaining further insights on the effect that the sequence and, especially, the stacking geometry have on the population transfer to the G → C CT.

Defect-mediated electron–phonon coupling in halide double perovskite

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the midgap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron–phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopic study of the thermal evolution of electron–phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron–phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm−1), which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated midgap states and the consequent existence of electron–phonon coupling in the double perovskite.

Direct View of Gate-Tunable Miniband Dispersion in Graphene Superlattices Near the Magic Twist Angle.

Superlattices from twisted graphene mono- and bilayer systems give rise to on-demand many-body states such as Mott insulators and unconventional superconductors. These phenomena are ascribed to a combination of flat bands and strong Coulomb interactions. However, a comprehensive understanding is lacking because the low-energy band structure strongly changes when an electric field is applied to vary the electron filling. Here, we gain direct access to the filling-dependent low-energy bands of twisted bilayer graphene (TBG) and twisted double bilayer graphene (TDBG) by applying microfocused angle-resolved photoemission spectroscopy to in situ gated devices. Our findings for the two systems are in stark contrast: the doping-dependent dispersion for TBG can be described in a simple model, combining a filling-dependent rigid band shift with a many-body-related bandwidth change. In TDBG, on the other hand, we find a complex behavior of the low-energy bands, combining nonmonotonous bandwidth changes and tunable gap openings, which depend on the gate-induced displacement field. Our work establishes the extent of electric field tunability of the low-energy electronic states in twisted graphene superlattices and can serve to underpin the theoretical understanding of the resulting phenomena.

Hydrogen and Pionic Atoms Under the Effects of Oscillations in the Global Monopole Spacetime

In this analysis, we investigate hydrogen and pionic atoms subjected to Dirac and Klein-Gordon oscillators, respectively, in the global monopole spacetime. Through a purely analytical analysis, we determine solutions of bound state, in which we define the allowed energy values for the lowest energy state of both proposed systems. In addition to the influence of the topological defect on the results obtained, we note another quantum effect: the oscillation frequencies of both systems depend on the system quantum numbers, that is, the angular frequencies are quantized.

Energy of Functional Brain States Correlates With Cognition in Adolescent-Onset Schizophrenia and Healthy Persons.

Adolescent-onset schizophrenia (AOS) is relatively rare, under-studied, and associated with more severe cognitive impairments and poorer outcomes than adult-onset schizophrenia. Neuroimaging has shown altered regional activations (first-order effects) and functional connectivity (second-order effects) in AOS compared to controls. The pairwise maximum entropy model (MEM) integrates first- and second-order factors into a single quantity called energy, which is inversely related to probability of occurrence of brain activity patterns. We take a combinatorial approach to study multiple brain-wide MEMs of task-associated components; hundreds of independent MEMs for various sub-systems were fit to 7 Tesla functional MRI scans. Acquisitions were collected from 23 AOS individuals and 53 healthy controls while performing the Penn Conditional Exclusion Test (PCET) for executive function, which is known to be impaired in AOS. Accuracy of PCET performance was significantly reduced among AOS compared with controls. A majority of the models showed significant negative correlation between PCET scores and the total energy attained over the fMRI. Severity of psychopathology was correlated positively with energy. Across all instantiations, the AOS group was associated with significantly more frequent occurrence of states of higher energy, assessed with a mixed effects model. An example MEM instance was investigated further using energy landscapes, which visualize high and low energy states on a low-dimensional plane, and trajectory analysis, which quantify the evolution of brain states throughout this landscape. Both supported patient-control differences in the energy profiles. The MEM's integrated representation of energy in task-associated systems can help characterize pathophysiology of AOS, cognitive impairments, and psychopathology.

Investigating the formation of metal nitride complexes employing a tetradentate bis-carbene bis-phenolate ligand.

The synthesis of MnV and CrV nitride complexes of a pro-radical tetradentate bis-phenol bis-N-heterocyclic carbene ligand H2LC2O2 was investigated. Employing either azide photolysis of the MnIII precursor complex MnLC2O2(N3) or a nitride exchange reaction between MnLC2O2(Br) and the nitride exchange reagent Mnsalen(N) failed to provide a useful route to the target nitride MnLC2O2(N). Experimental results support initial formation of the target nitride MnLC2O2(N), however, the nitride rapidly inserts into a Mn-CNHC bond. A second insertion reaction results in the isolation of the doubly inserted ligand product [H2LC2O2(N)]+ in good yield. In contrast, the Cr analogue CrLC2O2(N) was readily prepared and characterized by a number of experimental methods, including X-ray crystallography. Theoretical calculations predict a lower transition state energy for nitride insertion into the M-CNHC bond for Mn in comparison to Cr, and in addition the N-inserted product is stabilized for Mn while destabilized for Cr. Natural bond order (NBO) analysis predicts that the major bonding interaction (π MN → σ* M-CNHC) promotes nucleophilic attack of the nitride on the carbene as the major reaction pathway. Finally, one-electron oxidation of CrLC2O2(N) affords a relatively stable cation that is characterized by experimental and theoretical analysis to be a metal-oxidized d0 CrVI species.

Microscopic study on the low-energy quadrupole states in Ni isotopes

The main goal of this paper is to investigate the properties of the low-energy quadrupole strength in Ni isotopes, especially for the evolution of the pygmy quadrupole states with increasing neutron number. And the effect of shell evolution on the pygmy resonance is also discussed in detail. The Skyrme Hartree-Fock+Bardeen-Cooper-Schrieffer (HF+BCS) theory and the selfconsistent quasiparticle random phase approximation (RPA) method are employed on top of three effective Skyrme interactions named SGII, SLy5 and SKM<sup>*</sup>. In the calculations, a density-dependent zero-range type force are adopted for the pairing correlations. The properties of the first 2<sup>+</sup> state in Ni isotopes are studied firstly. As Fig. (a) shown, a good description on the experimental excited energies of the first 2<sup>+</sup> states are achieved, the SGII and SLy5 can give a good description on the reduced electric transition probabilities for <sup>58-68</sup>Ni. It is found that the energies of the first 2<sup>+</sup> state for <sup>68</sup>Ni and <sup>78</sup>Ni are obviously high than others, which reflects the obvious shell effect. In addition to the first 2<sup>+</sup> states, pygmy quadrupole states between 3 to 5 MeV with relative large electric transition probabilities are evidently found for <sup>70-76</sup>Ni in the isoscalar quadruple strength distribution [see Fig. (b)]. With the increasing of neutron number, the pygmy quadrupole states have decreasing energies but hold gradually increasing strengths, and it is more sensitive to the changes in the shell structure. This is due to the fact that the gradually filling of the neutron level 1<i>g</i><sub>9/2</sub> has an very important impact on the pygmy quadrupole states of <sup>70-76</sup>Ni, and switch from proton-dominated excitations to neutron-dominated ones. Since the pygmy quadrupole states for <sup>70-76</sup>Ni are sensitive to the proton and neutron shell gaps, which can provide information on the shell evolution in neutron-rich nuclei.

Systematic free energy insights into the enhanced dispersibility of myofibrillar protein in low-salt solutions through ultrasound-assisted enzymatic deamidation.

This work aimed to investigate the effects of ultrasound assisted enzymatic deamidation by protein-glutaminase (PG) on the dispersion of myofibrillar protein (MP) in low-salt solutions. The solubility, structural characteristics, transmission electron microscopy, asymmetric-flow field-flow fractionation, steady shear rheological property and multiple light scattering of MP deamidated by PG (MP-PG) and MP pretreated with ultrasound followed by PG deamidation (MP-U-PG) were determined. Molecular docking and molecular dynamics (MD) simulations were used to estimate the interaction between PG and MP. Under ultrasound assistance, the MP deamidated for 16h (MP-U-PG16) showed the highest solubility (80.1%) in low-salt conditions, which is attributed to its highest absolute zeta potential and smallest particle size. Although secondary structure analysis showed that MP-PG and MP-U-PG had an increased α-helix ratio and a decreased β-sheet ratio, ultrasonic treatment had a significantly influence on the MD results. The results manifested that hydrogen bond was the primary forces driving the binding between PG and MP, and the hydrogen bond and hydrophobic interaction were the dominant forces responsible the binding between PG and MP pretreated with ultrasound. According to the energy landscapes theory, ultrasound could overcome the energy barriers through external force input and find the best pathway to achieve the final lowest energy state. Our research contributed to the improvement of the colloidal dispersibility of MPs under low-salt conditions and the regulation of protein interaction by ultrasound assistance.

Gradient structure induced extra plasticity in a low-energy state metallic glass

Gradient structure induced extra plasticity in a low-energy state metallic glass

Cyclic quantum annealing: searching for deep low-energy states in 5000-qubit spin glass

Quantum computers promise a qualitative speedup in solving a broad spectrum of practical optimization problems. The latter can be mapped onto the task of finding low-energy states of spin glasses, which is known to be exceedingly difficult. Using D-Wave’s 5000-qubit quantum processor, we demonstrate that a recently proposed iterative cyclic quantum annealing algorithm can find deep low-energy states in record time. We also find intricate structures in a low-energy landscape of spin glasses, such as a power-law distribution of connected clusters with a small surface energy. These observations offer guidance for further improvement of the optimization algorithms.

Low-energy excited singlet states of para-aminothiophenol in methanol and n-hexane solutions

Optical absorption spectra of para-aminothiophenol in n-hexane and methanol solutions have been obtained. The calculation has been carried out using the TDDFT B3LYP/6-311+G(d,p) method taking into account the polarizable continuum model of the electronic spectra of the p-aminothiophenol molecule in n-hexane and its hydrogen-bonded complex with two methanol molecules in a methanol solution. Based on these calculations, the main absorption bands are interpreted and it is shown that the second excited singlet state is formed by a π → σ* electronic transition, which makes a significant contribution to the first absorption band of p-aminothiophenol in these solutions.

A reinforced lunar dynamo recorded by Chang'e-6 farside basalt.

The evolution of the lunar dynamo is essential for deciphering the deep interior structure, thermal history, and surface environment of the Moon1-4. Previous palaeomagnetic investigations on samples returned from the nearside of the Moon have established the general variation of the lunar magnetic field5-7. However, limited spatial and temporal palaeomagnetic constraints leave the evolution of the lunar dynamo ambiguous. The Chang'e-6 mission returned the first farside basalts dated at ca. 2.8 billion years ago (Ga)8,9, offering a unique opportunity to investigate a critical spatiotemporal gap in the evolution of the global lunar dynamo. Here we report palaeointensities (~5-21 μT) recovered from the Chang'e-6 basalts, providing the first constraint on the magnetic field from the lunar farside and a critical anchor within the large gap between 3 and 2 Ga. The new results record a rebound of the field strength after its prior sharp decline around 3.1 Ga, which attests to an active lunar dynamo at ca. 2.8 Ga in the mid-early stage and argues against the suggestion that the lunar dynamo may have remained in a low-energy state after 3 Ga until its demise. The result suggests the lunar dynamo was most likely driven by either a basal magma ocean and/or precession, probably supplemented by other mechanisms such as core crystallisation.

A Whole-Body Coordinated Motion Control Method for Highly Redundant Degrees of Freedom Mobile Humanoid Robots.

Humanoid robots are becoming a global research focus. Due to the limitations of bipedal walking technology, mobile humanoid robots equipped with a wheeled chassis and dual arms have emerged as the most suitable configuration for performing complex tasks in factory or home environments. To address the high redundancy issue arising from the wheeled chassis and dual-arm design of mobile humanoid robots, this study proposes a whole-body coordinated motion control algorithm based on arm potential energy optimization. By constructing a gravity potential energy model for the arms and a virtual torsional spring elastic potential energy model with the shoulder-wrist line as the rotation axis, we establish an optimization index function for the arms. A neural network with variable stiffness is introduced to fit the virtual torsional spring, representing the stiffness variation trend of the human arm. Additionally, a posture mapping method is employed to map the human arm potential energy model to the robot, enabling realistic humanoid movements. Combining task-space and joint-space planning algorithms, we designed experiments for single-arm manipulation, independent object retrieval, and dual-arm carrying in a simulation of a 23-degree-of-freedom mobile humanoid robot. The results validate the effectiveness of this approach, demonstrating smooth motion, the ability to maintain a low potential energy state, and conformity to the operational characteristics of the human arm.

Finding dense sublattices as low energy states of a Hamiltonian

Lattice-based cryptography has emerged as one of the most prominent candidates for postquantum cryptography, projected to be secure against the imminent threat of large-scale fault-tolerant quantum computers. The Shortest Vector Problem (SVP) is to find the shortest nonzero vector in a given lattice. It is fundamental to lattice-based cryptography and believed to be hard even for quantum computers. We study a natural generalization of the SVP known as the K-Densest Sublattice Problem (K-DSP): to find the densest K-dimensional sublattice of a given lattice. We formulate K-DSP as finding the first excited state of a Z-basis Hamiltonian, making K-DSP amenable to investigation via an array of quantum algorithms, including Grover search, quantum Gibbs sampling, adiabatic, and variational quantum algorithms. The complexity of the algorithms depends on the basis through which the input lattice is presented. We present a classical polynomial-time algorithm that takes an arbitrary input basis and preprocesses it into inputs suited to quantum algorithms. With preprocessing, we prove that O(KN2) qubits suffice for solving K-DSP for N-dimensional input lattices. We empirically demonstrate the performance of a quantum approximate optimization algorithm K-DSP solver for low dimensions, highlighting the influence of a good preprocessed input basis. We then discuss the hardness of K-DSP in relation to the SVP, to see if there is a reason to build postquantum cryptography on K-DSP. We devise a quantum algorithm that solves K-DSP with runtime exponent (5KNlog2N)/2. Therefore, for fixed K, K-DSP is no more than polynomially harder than the SVP. The central insight we use is similar in spirit to those underlying the best-known classical K-DSP algorithm due to Dadush and Micciancio. Whether the exponential dependence on K can be lowered remains an open question. Published by the American Physical Society 2024

Shallow donor states and interlevel transitions in gapped graphene bilayers

Abstract A variational calculation for the energies of the ground and first excited states of a shallow donor impurity in bilayer graphene (BLG) with an open energy gap is presented in this study. It is shown that the binding energies of the lowest states and the distance between them can be tuned in the region of few tens of meV by changing the gap and tight binding parameter γ 1 , which is responsible for the nearest neighboring interlayer coupling. Based on the results obtained, the optical transition of an impurity electron from the ground to the first excited state in BLG is investigated. We find that the oscillator strength of the transition between the lowest energy states 1 S → 2 P x of a shallow donor also depends on the gap and tight binding parameter γ 1 , but is not sensitive to the value of the cutting parameter of the soft Coulomb potential that is proposed. The transitions between shallow impurity levels in BLG can serve as an alternative tunable source of terahertz radiation. The possibility to tune the energy levels of hydrogenic-like impurities can open new ways for either the creation of coherent superpositions of the energy states or the coherent population transfer between them by applying laser pulses.

Electron beam-splitting effect with crossed zigzag graphene nanoribbons in high-spin metallic states

Here, we analyze the electron transport properties of a device formed of two crossed graphene nanoribbons with zigzag edges (ZGNRs) in a spin state with total magnetization different from zero. While the ground state of ZGNRs has been shown to display antiferromagnetic ordering between the electrons at the edges, for wide ZGNRs—where the localized spin states at the edges are decoupled and the exchange interaction is close to zero—in the presence of relatively small magnetic fields, the ferromagnetic (FM) spin configuration can become the state of lowest energy due to the Zeeman effect. In these terms, by comparing the total energy of a periodic ZGNR as a function of the magnetization per unit cell, we obtain the FM-like solution of the lowest energy for the perfect ribbon, the corresponding FM-like configuration of the lowest energy for the four-terminal device formed of crossed ZGNRs, and the critical magnetic field needed to excite the system to this spin configuration. By performing transport calculations, we analyze the role of the distance between layers and the crossing angle of this device in the electrical conductance, at small gate voltages. The problem is approached employing the mean-field Hubbard Hamiltonian in combination with non-equilibrium Green’s functions. We find that ZGNR devices subject to transverse magnetic fields may acquire a high-spin configuration that ensures a metallic response and tunable beam-splitting properties, making this setting promising for studying electron quantum optics with single-electron excitations.