Odd Number Of Electrons Research Articles

Adsorption of Ag, Au, Cu, and Ni on MoS2: theory and experiment

Here, we present results of a computational and experimental study of adsorption of various metals on MoS2. In particular, we analyzed the binding mechanism of four metallic elements (Ag, Au, Cu, Ni) on MoS2. Among these elements, Ni exhibits the strongest binding and lowest mobility on the surface of MoS2. On the other hand, Au and Ag bond very weakly to the surface and have very high mobilities. Our calculations for Cu show that its bonding and surface mobility are between these two groups. Experimentally, Ni films exhibit a composition characterized by randomly oriented nanoscale clusters. This is consistent with the larger cohesive energy of Ni atoms as compared with their binding energy with MoS2, which is expected to result in 3D clusters. In contrast, Au and Ag tend to form atomically flat plateaued structures on MoS2, which is contrary to their larger cohesive energy as compared to their weak binding with MoS2. Cu displays a surface morphology somewhat similar to Ni, featuring larger nanoscale clusters. However, unlike Ni, in many cases Cu exhibits small plateaued surfaces on these clusters. This suggests that Cu likely has two competing mechanisms that cause it to span the behaviors seen in the Ni and Au/Ag film morphologies. These results indicate that calculations of the initial binding conditions could be useful for predicting film morphologies. In addition, out calculations show that the adsorption of adatoms with odd electron number like Ag, Au, and Cu results in 100% spin-polarization and integer magnetic moment of the system. Adsorption of Ni adatoms, with even electron number, does not induce a magnetic transition.

An Efficient Algorithm for Constrained CASSCF(1,2) and CASSCF(3,2) Simulations as Relevant to Electron and Hole Transfer Problems.

We propose an efficient algorithm for the recently published electron/hole-transfer Dynamical-weighted State-averaged Constrained CASSCF (eDSC/hDSC) method studying charge transfer states and D1-D0 crossings for systems with odd numbers of electrons. By separating the constrained minimization problem into an unconstrained self-consistent-field (SCF) problem and a constrained nonself-consistent-field (nSCF) problem, as well as accelerating the direct inversion in the iterative subspace (DIIS) technique to solve the SCF problem, the overall computational cost is reduced by a factor of 8-20 compared with directly using sequential quadratic programming (SQP). This approach should be applicable for other constrained minimization problems, and in the immediate future, once gradients are available, the present eDSC/hDSC algorithm should allow for speedy nonadiabatic dynamics simulations.

Hidden magnetism and split off flat bands in the insulator metal transition in VO2

Transition metal d-electron oxides with an odd number of electrons per unit cell are expected to form metals with partially occupied energy bands, but exhibit in fact a range of behaviors, being either insulators, or metals, or having insulator-metal transitions. Traditional explanations involved predominantly electron-electron interactions in fixed structural symmetry. The present work focuses instead on the role of symmetry breaking local structural motifs. Viewing the previously observed V-V dimerization in VO2 as a continuous knob, reveals in density functional calculations the splitting of an isolated flat band from the broad conduction band. This leads past a critical percent dimerization to the formation of the insulating phase while lowering the total energy. In VO2 this transition is found to have a rather low energy barrier approaching the thermal energy at room temperature, suggesting energy-efficient switching in neuromorphic computing. Interestingly, sufficient V-V dimerization suppresses magnetism, leading to the nonmagnetic insulating state, whereas magnetism appears when dimerization is reduced, forming a metallic state. This study opens the way to design novel functional quantum materials with symmetry breaking-induced flat bands.

A fast and smooth one-electron approach for investigating charge transfer states and D1-D0 crossings for systems with odd numbers of electrons.

We propose an efficient version of ensemble Hartree-Fock/density functional theory to calculate a set of two charge-transfer states for systems with odd-numbers of electrons. The approach does require definitions of donor/acceptor fragments; however, the approach is not very sensitive to such definitions-even in the limit of very strong electronic coupling. The key ansatz is that, by mandating that the vector space spanned by the active orbitals projects equally onto the donor and acceptor fragments, such a constraint eliminates all intra-molecular local excitations and makes it far easier to generate potential energy surfaces that are smooth over a wide region of configuration space. The method is fast, working with only two electron configurations, and should be useful for abinitio non-adiabatic dynamics in the near future.

Antioxidant and cytotoxicity evaluation of the Endophytic Fungus, Fusarium equiseti, isolated from the leaves of Ocimum gratissimum

Antioxidants serve as defense mechanisms which protects against oxidative damage through preventing or retarding oxidation caused by free radicals. Free radicals are highly reactive molecules with an odd number of electrons generated from oxygen capable of damaging various cellular structures. Endophytes have shown capacity to create beneficial biologically active molecules with a wide range of pharmacological properties usually identical to those of the host plant. Their feature has continued to gain fame due to their ability to produce metabolites within the host system without causing harm to the host while sequestering reactive oxygen species within the host systems. Endophytic fungal isolation, fungal fermentation, extraction of secondary metabolites, antioxidant and cytotoxicity studies were carried out using standard laboratory methods. Therefore, this study evaluated the antioxidant and cytotoxicity activity of fusarium equiseti previously isolated from Ocimum gratissimum. The findings revealed that the crude extract of an endophyte associated with O. gratissimum called F. equiseti produced substances that have strong antioxidant and cytotoxic properties. The antioxidant and cytotoxic potential were due to presence of compounds previously reported for cytotoxic activity, such as Enniatins and Sarasinoside H1 and while the antioxidant activity was due to presence of Orientin a compound known to have shown antioxidant property. Therefore, this endophyte may serve as a source of new substances with potential for use in pharmaceutical applications for diseases associated with reactive oxygen species.

Time-reversal symmetry adaptation in relativistic density matrix renormalization group algorithm.

In the nonrelativistic Schrödinger equation, the total spin S and spin projection M are good quantum numbers. In contrast, spin symmetry is lost in the presence of spin-dependent interactions, such as spin-orbit couplings in relativistic Hamiltonians. Therefore, the relativistic density matrix renormalization group algorithm (R-DMRG) only employing particle number symmetry is much more expensive than nonrelativistic DMRG. In addition, artificial breaking of Kramers degeneracy can happen in the treatment of systems with an odd number of electrons. To overcome these issues, we propose time-reversal symmetry adaptation for R-DMRG. Since the time-reversal operator is antiunitary, this cannot be simply achieved in the usual way. We introduce a time-reversal symmetry-adapted renormalized basis and present strategies to maintain the structure of basis functions during the sweep optimization. With time-reversal symmetry adaptation, only half of the renormalized operators are needed, and the computational costs of Hamiltonian-wavefunction multiplication and renormalization are reduced by half. The present construction of the time-reversal symmetry-adapted basis also directly applies to other tensor network states without loops.

Variable and Orbital-Dependent Spin-Orbit Field Orientations in an InSb Double Quantum Dot Characterized via Dispersive Gate Sensing

Utilizing dispersive gate sensing (DGS), we investigate the spin-orbit field (${\mathbf{B}}_{\mathrm{SO}}$) orientation in a many-electron double quantum dot (DQD) defined in an $\mathrm{In}\mathrm{Sb}$ nanowire. While characterizing the interdot tunnel couplings, we find the measured dispersive signal depends on the electron-charge occupancy, as well as on the amplitude and orientation of the external magnetic field. The dispersive signal is mostly insensitive to the external field orientation when a DQD is occupied by a total odd number of electrons. For a DQD occupied by a total even number of electrons, the dispersive signal is reduced when the finite external magnetic field aligns with the effective ${\mathbf{B}}_{\mathrm{SO}}$ orientation. This fact enables the identification of ${\mathbf{B}}_{\mathrm{SO}}$ orientations for different DQD electron occupancies. The ${\mathbf{B}}_{\mathrm{SO}}$ orientation varies drastically between charge transitions, and is generally neither perpendicular to the nanowire nor in the chip plane. Moreover, ${\mathbf{B}}_{\mathrm{SO}}$ is similar for pairs of transitions involving the same valence orbital, and varies between such pairs. Our work demonstrates the practicality of DGS in characterizing spin-orbit interactions in quantum dot systems, without requiring any current flow through the device.

Interactions of nitric oxide molecules with pure and oxidized silver clusters Agn ±/AgnO± (n=11-13): A computational study.

In this work, we have studied, within density functional theory, the interaction of NO with pure and oxidized silver clusters, both anionic and cationic, composed from 11 to 13 Ag atoms. In that size interval, shell closing effects are not expected, and structural and electronic odd-even effects will determine the strength of interaction. First, we obtained that species Agn ± and AgnO± with odd number of electrons (n = 12) adsorb NO with higher energy than their neighbors (n = 11 and 13). This result is in agreement with the facts observed in recent mass spectroscopy measurements, which were performed, however, at finite temperature. The adsorption energy is about twice for oxidized clusters compared to pure ones and higher for anions than for cations. Second, the adsorption of another NO molecule on AgnNO± forms Agn(NO)2 ±, with the dimer (NO)2 in cis configuration, and binding the two N atoms with two neighbor Ag atoms. The n = 12 species show the higher adsorption energy again. Third, in the absence of reaction barriers, all complexes Agn(NO)2 ± dissociate spontaneously into AgnO± and N2O, except the n = 12 anion. The maximum high barrier along the dissociation path of Ag13(NO)2 - is about 0.7eV. Further analysis of projected density of states for Ag11-13(NO)x ± (x = 0, 1, 2) molecules shows that bonding between NO and Ag clusters mainly occurs in the energy range between -3.0 and 3.0eV. The overlap between 4d of Ag and 2p of N and O is larger for Ag12(NO)2 ± than for neighbor sizes. For n = 12, the d bands are close to the (NO)22π orbital, leading to extra back-donation charge from the 4d of Ag to the closer 2π orbital of (NO)2.

Theoretical study on exohedral complexes C6H6TMB40 (TM = Sc-Ni).

Exohedral borospherene complexes comprised of 3d transition metal (TM) atoms with borospherene B40 and benzene (C6H6) molecules, C6H6TMB40, were systematically studied by using density functional theory (DFT). Results show that in the ground states, the bonding type between TM and B40 changes from η7 (TM = Sc-V) to η6 (TM = Cr-Fe) and then to η7 (TM = Co, Ni) with the increasing number of d electrons. Except for C6H6TiB40 and C6H6FeB40 being triplets, all C6H6TMB40 clusters have the lowest spin. Namely, the ground spin state with an even number of electrons is a singlet state, and the ground spin state with an odd number of electrons is a doublet state. The investigated C6H6TMB40 clusters (TM = Sc-Ni) possess higher stabilities through the ionic-covalent interactions between transition metals, benzene and the B40 cage.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

Understanding the stability and reactivity of silver clusters toward oxygen provides insights to design new materials of coinage metals with atomic precision. Herein, we report a systematic study o...

Structures and Properties of CoB19 +/0/- Clusters.

A global search for the lowest energy structure of Co atom-doped boron clusters (CoB19+, CoB19, and CoB19– clusters) was conducted. The lowest energy structures of them are remarkably different from those of B20 and CoB18– clusters. CoB19+ clusters have a bowl-shaped geometry, where the Co atom is at the bottom of the bowl and is coordinated with eight B atoms. The CoB19 cluster presents seven- and eight-membered B rings. The CoB19– cluster can be viewed as a structure that evolves from a Co-doped boron plane. The coordination number of CoB19 and CoB19– clusters are 16 and 14, respectively. Several low-lying isomers have quasi-planar structures for the CoB19– cluster. Some properties including charge transformation and distribution, HOMO–LUMO gaps, molecular orbital distribution, and stability of neutral CoB19 are discussed. CoB19+ and CoB19– exhibit magnetism with a net moment of 1.0 and 0.94 μB because of odd number of electrons.

Bifluxon: Fluxon-Parity-Protected Superconducting Qubit

We have developed and characterized a symmetry-protected superconducting qubit that offers simultaneous exponential suppression of energy decay from charge and flux noise, and dephasing from flux noise. The qubit consists of a Cooper-pair box (CPB) shunted by a superinductor, thus forming a superconducting loop. Provided the offset charge on the CPB island is an odd number of electrons, the qubit potential corresponds to that of a $\cos \phi / 2$ Josephson element, preserving the parity of fluxons in the loop via Aharonov-Casher interference. In this regime, the logical-state wavefunctions reside in disjoint regions of phase space, thereby ensuring the protection against energy decay. By switching the protection on, we observed a ten-fold increase of the decay time, reaching up to $100 \mu \mathrm{s}$. Though the qubit is sensitive to charge noise, the sensitivity is much reduced in comparison with the charge qubit, and the charge-noise-induced dephasing time of the current device exceeds $1 \mu \mathrm{s}$. Implementation of the full dephasing protection can be achieved in the next-generation devices by combining several $\cos \phi / 2$ Josephson elements in a small array.

Chemical Reaction Rates for Systems with Spin-Orbit Coupling and an Odd Number of Electrons: Does Berry's Phase Lead to Meaningful Spin-Dependent Nuclear Dynamics for a Two State Crossing?

Within the context of a simple avoided crossing, we investigate the effect of a complex-valued diabatic coupling in determining spin-dependent rate constants and scattering states. We find that, if the molecular geometry is not linear and the Berry force is not zero, one can find significant spin polarization of the products. This study emphasizes that, when analyzing nonadiabatic reactions with spin orbit coupling (and a complex-valued Hamiltonian), one must consider how Berry force affects nuclear motion-at least in the context of gas phase reactions. Work is currently ongoing as far as extrapolating these conclusions to the condensed phase, where interesting spin selection has been observed in recent years.

Low-temperature insulating phase of the Si(111)–7×7 surface

We investigated the electronic structure of the Si(111)--7$\times$7 surface below 20 K by scanning tunneling and photoemission spectroscopies and by density functional theory calculations. Previous experimental studies have questioned the ground state of this surface, which is expected to be metallic in a band picture because of the odd number of electrons per unit cell. Our differential conductance spectra instead show the opening of an energy gap at the Fermi level and a significant temperature dependence of the electronic properties, especially for the adatoms at the center of the unfaulted half of the unit cell. Complementary photoemission spectra with improved correction of the surface photovoltage shift corroborate the differential conductance data and demonstrate the absence of surface bands crossing the Fermi level at 17 K. These consistent experimental observations point to an insulating ground state and contradict the prediction of a metallic surface obtained by density functional theory in the generalized gradient approximation. The calculations indicate that this surface has or is near a magnetic instability, but remains metallic in the magnetic phases even including correlation effects at mean-field level. We discuss possible origins of the observed discrepancies between experiments and calculations.

Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2

If a material with an odd number of electrons per unit-cell is insulating, Mott localisation may be invoked as an explanation. This is widely accepted for the layered compound 1T-TaS2, which has a low-temperature insulating phase comprising charge order clusters with 13 unpaired orbitals each. But if the stacking of layers doubles the unit-cell to include an even number of orbitals, the nature of the insulating state is ambiguous. Here, scanning tunnelling microscopy reveals two distinct terminations of the charge order in 1T-TaS2, the sign of such a double-layer stacking pattern. However, spectroscopy at both terminations allows us to disentangle unit-cell doubling effects and determine that Mott localisation alone can drive gap formation. We also observe the collapse of Mottness at an extrinsically re-stacked termination, demonstrating that the microscopic mechanism of insulator-metal transitions lies in degrees of freedom of inter-layer stacking.

Kubo spins in nanoscale aluminum grains: A muon spin relaxation study

We report muon spin relaxation rate measurements on films composed of aluminum grains having a size of a few nm, with a large energy level splitting of the order of 100 K. The films range from weakly metallic to insulating. In the insulating case the low temperature relaxation rate is consistent with the presence of single electron spins in grains having an odd number of electrons. The relaxation rate temperature dependence follows an activation law having an energy scale in agreement with the average level splitting. In weakly metallic films the relaxation rate is smaller and decreases faster with temperature. Overall our observations are in line with the presence of a Kubo spin in Al nano-size grains due to quantum size effects.

Spin-orbit excitons in CoO

CoO has an odd number of electrons in its unit cell, and therefore is expected to be metallic. Yet, CoO is strongly insulating owing to significant electronic correlations, thus classifying it as a Mott insulator. We investigate the magnetic fluctuations in CoO using neutron spectroscopy. The strong and spatially far-reaching exchange constants reported in [Sarte et al. Phys. Rev. B 98 024415 (2018)], combined with the single-ion spin-orbit coupling of similar magnitude [Cowley et al. Phys. Rev. B 88, 205117 (2013)] results in significant mixing between $j_{eff}$ spin-orbit levels in the low temperature magnetically ordered phase. The high degree of entanglement, combined with the structural domains originating from the Jahn-Teller structural distortion at $\sim$ 300 K, make the magnetic excitation spectrum highly structured in both energy and momentum. We extend previous theoretical work on PrTl$_{3}$ [Buyers et al. Phys. Rev. B 11, 266 (1975)] to construct a mean-field and multi-level spin exciton model employing the aforementioned spin exchange and spin-orbit coupling parameters for coupled Co$^{2+}$ ions on a rocksalt lattice. This parameterization, based on a tetragonally distorted type-II antiferromagnetic unit cell, captures both the sharp low energy excitations at the magnetic zone center, and the energy broadened peaks at the zone boundary. However, the model fails to describe the momentum dependence of the excitations at high energy transfers, where the neutron response decays faster with momentum than the Co$^{2+}$ form factor. We discuss such a failure in terms of a possible breakdown of localized spin-orbit excitons at high energy transfers.

Ab-initio calculations of chemical and optoelectronic properties of 7-atom Pt-Y [Y = Li, Na, K

Using density functional theory, we investigated structural, chemical, electronic, and optical properties of the 7 neutral atom Pt-Y [Y = Li, Na, K] pure and nanoalloys. The generalized gradient approximation and ultrasoft pseudopotential are considered. Interesting results are achieved. In particular, Pt6Li cluster shows a higher absolute value of the binding energy (BE) whereas in all other Pt7-mYm systems, this value decreases when m increases. The more the atomic radius increases, the less the resulting alkali metal nanoclusters are cohesive. The most stable structure of Pt7-mYm cluster is obtained when m = 4 for Li and Na atoms, whereas for K atom, this occurs for m = 3. Moreover, the calculated absorption spectra of the Pt7-mYm (m = 2, 4, 6) have revealed that the doping with Li, Na, and K widens the absorption band. Also, the absorption spectra obtained are more pronounced in the low energy zone. It appears that the electron absorption strength is high in low excitation energy zone. On the other hand, the nanoclusters with m = 1, 3, 5, 7 (odd numbers of electrons) showed metallic character with absorption spectra that could not be easily guessed through the present numerical calculations. The nanoclusters Pt7-mYm with even numbers of dopant atoms showed semiconductor properties with the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap increasing as the number of doping atoms increases.

Relativistic multimode pseudo-Jahn-Teller effect in planar molecules YX3 with D3h′ symmetry

• Relativistic multimode pseudo-Jahn-Teller effect 2 E ′ + 2 A 2 ″ × e ′ + a 2 ″ . • Planar tetratomic molecules Y X 3 with the odd number of electrons. • Double symmetry group D 3 h ′ . • Symmetry properties of electronic Hamiltonian. • Spin-orbit coupling terms. • Second order terms for electrostatic and spin-orbit contributions. • 6 × 6 vibronic matrix. • e ′ and a 2 ″ vibration normal modes. • 9 electrostatic and 10 spin-orbital real constant parameters. Relativistic multimode pseudo-Jahn-Teller effect 2 E ′ + 2 A 2 ″ × e ′ + a 2 ″ is considered for planar tetratomic molecules Y X 3 , which have the odd number of electrons and are characterized by the double symmetry group D 3 h ′ . Our analysis is based on the symmetry properties of electronic Hamiltonian, which includes spin-orbit coupling terms. Taylor series expansion of electronic Hamiltonian in terms of vibration normal modes e ′ and a 2 ″ is restricted by second order terms for electrostatic and spin-orbit contributions. The result of this research is 6 × 6 vibronic matrix, which depends on e ′ and a 2 ″ vibration normal modes and includes nine electrostatic and ten spin-orbital real constant parameters.

Quasiparticle band structure and spin excitation spectrum of the Kondo lattice

A formulation of the Kondo lattice Hamiltonian in terms of bond particles is derived and solved in two different approximations. The bond particles correspond to the eigenstates of a single unit cell and are bosons for states with even electron number and fermions for states with an odd electron number. A s a check various physical quantities are calculated for the 1D Kondo insulator a nd good agreement with numerical results is obtained for J/t>1.