State Geometry Research Articles

Understanding localized states in the band tails of amorphous semiconductors exemplified by a -Si:H from the perspective of excess delocalized charges

In this paper, we use a perturbation strategy to show that the band tails in the density of states (DOS) distribution of amorphous semiconductors form due to the existence of excess delocalized charges. These charges satisfy a Gaussian distribution with a mean of zero and vary slowly in space due to the short- and medium-range order of amorphous materials. The charges exist due to the bond angle and bond length distortion. They induce an extra potential energy distribution that leads to energy band fluctuation in the energy-space diagram and consequently gives rise to localized states. A 150×150×7.5 nm large-scale finite-element excess charge model for hydrogenated amorphous silicon (a-Si:H) is developed using a moving average smoothing that filters a Gaussian array of random charge values. Thanks to the analytical and computational simplicity of the theory in this paper (compared with conventional approaches considering atomistic details and complex electron-electron interactions), this large-scale model is calculated in only 90 s and reproduces the typical exponential and linear features found in the conduction band tail of a-Si:H and other amorphous semiconductors. Through a satisfactory fitting to experimental a-Si:H DOS data in the literature, model parameters are semiquantitatively determined. Unlike previous analytical and computational efforts, this large-scale model is physically unambiguous, computationally tractable, and satisfactorily accurate. The large-scale modeling capability allows reliable insights into the geometric features of localized and extended states, which are visualized in a nonschematic manner. This further leads to reinvestigations of several established concepts and conclusions. First, calculations in this paper challenge the description that the wave function envelope of a localized state decays away from its center in an exponential manner and that the spread of this exponential decay varies with energy in a power-law manner. Second, impurity states and/or extended states are critical to enable band tail hopping. Third, low-energy states are spatially included inside high-energy states, so the existing concept of average spatial separation of localized states is meaningless. Fourth, the mobility edge obtained from conductivity activation energy measurements turns out to be higher than the actual critical energy Ect that demarcates extended states from localized states; this judgment is supported by the electron mobility-energy relation that is inferred from the geometry of states, which validates a continuous increase of energy-specific mobility as electron energy increases from Ect. Published by the American Physical Society 2024

On the geometry of two state models for the colored Jones polynomial

Using the flow property of the [Formula: see text]-matrix defining the colored Jones polynomial, we establish a natural bijection between the set of states on the part arc-graph of a link projection and the set of states on a corresponding bichromatic digraph, called arc-graph, as defined by Garoufalidis and Loebl [A non-commutative formula for the colored Jones function, Math. Ann. 336 (2006) 867–900]. We use this to give a new and essentially elementary proof for the knot state-sum formula in [S. Garoufalidis and M. Loebl, A non-commutative formula for the colored Jones function, Math. Ann. 336 (2006) 867–900]. We will show that the state-sum contributions of states on the part arc-graph defined by the universal [Formula: see text]-matrix of [Formula: see text] correspond, under our bijection of sets of states, to the contributions in [S. Garoufalidis and M. Loebl, A non-commutative formula for the colored Jones function, Math. Ann. 336 (2006) 867–900]. This will show that the two state models are in fact not essentially distinct. Our approach will also extend the formula of Garoufalidis and Loebl to links. This requires some additional nontrivial observations concerning the geometry of states on the part arc-graphs. We will discuss in detail the computation of the arc-graph state-sum, in particular for [Formula: see text]-braid closures.

Spiral Donor Design Strategy for Blue Thermally Activated Delayed Fluorescence Emitters.

Thermally activated delayed fluorescence (TADF) emitters with a spiral donor show tremendous potential toward high-level efficient blue organic light-emitting diodes (OLEDs). However, the underlying design strategy of the spiral donor used for blue TADF emitters remains unclear. As a consequence, researchers often do "try and error" work in the development of new functional spiral donor fragments, making it slow and inefficient. Herein, we demonstrate that the energy level relationships between the spiral donor and the luminophore lead to a significant effect on the photoluminescent quantum yields (PLQYs) of the target materials. In addition, a method involving quantum chemistry simulations that can accurately predict the aforementioned energy level relationships by simulating the spin density distributions of the triplet excited states of the spiral donor and corresponding TADF emitters and the triplet excited natural transition orbitals of the TADF emitters is established. Moreover, it also revealed that the steric hindrance in this series of molecules can form a nearly unchanged singlet (S1) state geometry, leading to a reduced nonradiative decay and high PLQY, while a moderated donor-acceptor (D-A) torsion in the triplet (T1) state can induce a strong vibronic coupling between the charge-transfer triplet (3CT) state and the local triplet (3LE) state, achieving an effective reverse intersystem crossing (RISC) process. Furthermore, an electric-magnetic coupling is formed between the high-lying 3LE state and the charge-transfer singlet (1CT) state, which may open another RISC channel. Remarkably, in company with the optimized molecular structure and energy alignment, the pivotal TADF emitter DspiroS-TRZ achieved 99.9% PLQY, an external quantum efficiency (EQE) of 38.4%, which is the highest among all blue TADF emitters reported to date.

Keggin-type polyoxometalate 1 : 1 complexes of Pb(II) and Bi(III): experimental, theoretical and luminescence studies.

Bi3+ and Pb2+ uptake by a monolacunary Keggin-type [PW11O39]7- anion leads to the formation of [PW11O39Bi]4- and [PW11O39Pb]5- complexes with a stereochemically active lone pair at the incorporated heterometal. The two complexes were isolated as (TBA)4[PW11O39Bi] (1) and (TBA)5[PW11O39Pb] (2) and characterized by 31P and 183W NMR spectroscopy, high-resolution electrospray mass-spectrometry (HR-ESI-MS) and cyclic voltammetry (CV). EXAFS and XANES data confirm the unchanged oxidation state and ψ-square pyramidal geometry of Bi3+ and Pb2+ in 1 and 2. DFT calculations were used in order to (i) confirm the absence of ligands attached to the heterometal sites in both complexes and localize the lone pair, and (ii) assign all signals in the 183W NMR spectra. Complexes 1 and 2 demonstrate photoluminescence (PL). A reversible change in the PL spectra of both complexes in the presence of water vapor has been detected. On the contrary, PL data for sandwich-type ((CH3)4N)4K3[H4(PW11O39)2Bi]·25H2O (3) do not show sensitivity to water vapor.

Spacetime from bits.

In the anti-de Sitter/conformal field theory approach to quantum gravity, the spacetime geometry and gravitational physics of states in some quantum theory of gravity are encoded in the quantum states of an ordinary nongravitational system. Here, I demonstrate that this nongravitational system can be replaced with an arbitrarily large collection of noninteracting systems ("bits") placed in a highly entangled state. This construction makes manifest the idea that spacetime geometry emerges from entanglement between the fundamental degrees of freedom of quantum gravity and that removing this entanglement is tantamount to disintegrating spacetime. This setup also reveals that the entangled states encoding spacetimes may be well represented by a certain type of tensor network in which the individual tensors are associated with states of small numbers of bits.

Theoretical Investigation of Design Methodology, Optimized Molecular Geometries, and Electronic Properties of Benzene-Based Single Molecular Switch with Metal Nanoelectrodes

Understanding the electronic properties at the single molecular level is the first step in designing functional electronic devices using individual molecules. This paper proposes a simulation methodology for the design of a single molecular switch. A single molecular switch has two stable states that possess different chemical configurations. The methodology is implemented for 1,4-benzene dithiol (BDT) molecule with gold, silver, platinum, and palladium metal nanoelectrodes. The electronic properties of the designed metal-molecule-metal sandwich structure have been investigated using density functional theory (DFT) and Hartree-Fock (HF) method. It has been perceived that the DFT and HF values are slightly different as HF calculation does not include an electron-electron interaction term. Computation of the switching ratio gives the insight that BDT with gold has a high switching ratio of 0.88 compared with other three metal nanoelectrodes. Further, calculations of quantum chemical descriptors, analysis of the density of states (DOS) spectrum, and frontier molecular orbitals for both the stable states (i.e., ON and OFF state geometries) have been carried out. Exploring the band gap, ionization potential, and potential energy of two stable states reveals that the ON state molecule shows slightly higher conductivity and better stability than the OFF state molecule for every chosen electrode in this work. The proposed methodology for the single molecular switch design suggests an eclectic promise for the application of these new materials in novel single molecular nanodevices.

Density Functional Theory Studies on the Real and Apparent Water-Exchange Reaction Kinetics of Al3+ in Aqueous Solution

The dissociative (D) mechanistic water-exchange kinetics of aquated Al3+ in aqueous solution is systematically studied using the density functional theory-quantum chemical cluster model (DFT-CM) method. The modeled pathways include dehydration of the hexacoordinated Al(H2O)63+ and successive hydration of the pentacoordinated Al(H2O)53+. For the hydration of Al(H2O)53+, the attacking pathways corresponding to the second-shell solvent water molecules at different sites are investigated. The gas phase-supermolecule-polarizable continuum model (GP-SM-PCM) is used to simulate the explicit and bulk solvation effects. The reactant, transition state, and product geometries of the modeled reaction pathways are optimized at the B3LYP/6-311+G(d,p) level of theory. The real and apparent water-exchange reaction mechanisms of Al3+ are analyzed based on the Gibbs free energy changes for the dehydration and hydration pathways. The possible ligand competition with the solvent water molecules in the formation of aqueous Al...

A Computational Study of 2-(chloromethyl)oxirane Ring Opening by Bromide and Acetate Anions Considering Electrophilic Activation with Cations of Alkali Metals

Ring opening of 2-(chloromethyl)oxirane via the nucleophilic substitution with bromide and acetate anions was investigated using density functional theory (DFT) calculations. It was shown that the geometry of the transition states and the activation parameters of the reactions correspond to those of SN2-like mechanism. The nature of localized transition states was analyzed using More O’Ferrall – Jencks plots. The quantum chemical simulations of the potential energy surface for the ring-opening reaction of oxirane by nucleophiles confirmed the theoretical assumptions about the favored path of interactions, which is a backside α-attack of nucleophile. The effect of alkali metal cation (Li+, Na+, K+) on that path was estimated. It was found that the electrophilic activation with alkali metal cation is more pronounced in the reaction of 2-(chloromethyl)oxirane with dissociated ions, than with ionic pairs.

Solvent Effect on The Equilibrium and Rate Constant of the Tautomeric Reaction in Nexium, Skelaxin, Aldara and Efavirenz Drugs: A Dft Study

Some drugs have two tautomeric structures in the liquid state and the tautomeric equilibrium is formed between these structures. The reaction rate and equilibrium constant of this reaction varies in different solvents. Thus, the determination of the appropriate solvent to separate tautomers is important. In this research, we used the DFT level of B3LYP and the 6-311++G** basis set to obtain the proper solvent for Nexium, Skelaxin, Aldara and Efavirenz drugs. All calculations were made above the melting point of the mentioned drugs, because these drugs are solid at room temperature. The solvent effect is included in the calculation utilizing the polarizable continuum model PCM. The transition state of the tautomeric reaction is determined using the quadratic synchronous transit (QST2) method. The geometry, energy, and dipole moment of transition states are analyzed in different solvent. The root mean square deviation (RMSD) analysis is performed to determine the degree of a structure deviation of tautomer 1 and tautomer 2 from the transition state in different solvents. It is found that the RMSD value for tatumer1 is higher than that for tautomer 2 in all studied drugs. The proper solvent for the separation of tautomers is determined from the analysis of thermodynamics and kinetics.

Triangle Geometry for Qutrit States in the Probability Representation

We express the matrix elements of the density matrix of the qutrit state in terms of probabilities associated with artificial qubit states. We show that the quantum statistics of qubit states and observables is formally equivalent to the statistics of classical systems with three random vector variables and three classical probability distributions obeying special constrains found in this study. The Bloch spheres geometry of qubit states is mapped onto triangle geometry of qubits. We investigate the triada of Malevich’s squares describing the qubit states in quantum suprematism picture and the inequalities for the areas of the squares for qutrit (spin-1 system). We expressed quantum channels for qutrit states in terms of a linear transform of the probabilities determining the qutrit-state density matrix.

Theoretical study of two states reactivity of NO activation on iron atom

The mechanism of Fe+NO was calculated by the Density Functional Theory (DFT) with the B3LYP methods combined with the 6-311+G (d, p) basis set. The geometry of reactants, transition states, intermediates and products of two reaction systems were completely optimized, and all the transition states were verified by the vibration analysis and intrinsic reaction coordinate (IRC) calculations. The “Two State Reactivity (TSR)” was used to analyze the reaction mechanisms; Results showed that the reaction system preferentially involves low-spin state entrance channel and the high-spin state exit channel. In the reaction channel, the crossing point appears, which would effectively reduce the activation energy and increase the release of reaction heat, play a significant and beneficial role in the kinetic and thermodynamic aspects of this catalytic reaction.

A first principles study on the active adsorbates on the hydrogenated diamond surface

Hydrogenated diamond film exhibits a high surface conductivity, which is very suitable for many in-plane microelectronic and microelectrochemical devices. However, the surface conductivity mechanism of hydrogenated diamond film remains unclear up to now. It inevitably retards its further applications. This work is to elucidate the effects of active adsorbate and water molecule on surface conductivity of hydrogenated diamond film. By the first principles method based on density functional theory, several models corresponding to hydrogenated and oxygenated diamond (100) surfaces physisorbed with various active adsorbates are built up. The adsorbed species include H3O+ ion mixed with H2O molecules with different concentrations. The adsorption energy, equilibrium geometry and density of states corresponding to the adsorption system are investigated. At the same time, the electron populations for different atoms of the physisorbed adsorbates are studied. The results show that the equilibrium geometry of H3O+ ion relaxes significantly after adsorption on hydrogenated diamond (100) surface. In addition, its adsorption energy increases dramatically compared with the system of individual H2O molecule adsorbed on hydrogenated diamond (100) surface. It follows that the strong interactions occur between H3O+ ion and hydrogenated diamond surface. With the concentration of the adsorbed H2O molecules increasing, the adsorption energy between the adsorbate and hydrogenated diamond (100) surface decreases gradually. It indicates that the interactions between H3O+ ion and the substrate weaken as the water molecule concentration increases. Concerning the electronic structure of H3O+ ion adsorbed on hydrogenated diamond (100) surface, shallow acceptors appear near Fermi level, which arises from charge transfer from hydrogenated diamond surface to adsorbed H3O+ ion. Therefore, hydrogenated diamond surface exhibits a p-type conductivity. With regard to the mixed adsorptions of H3O+ ion and H2O molecule, no significant effect on its conductivity is detected, though its surface energy band structure changes. At the same time, the electron transfers from hydrogenated diamond (100) surfaces to the adsorbates are also similar for all the systems with the adsorbates including one H3O+ ion and different H2O molecules. Thus, the adsorbed H2O molecule concentration in this work has no effect on the surface conductivity of hydrogenated diamond surface. However, the adsorbates containing H2O molecules and H3O+ ion physisorbed on oxygenated diamond (100) surfaces do not exist stably. The H3O+ ion will decompose into one H2O molecule and one H atom, which form HO bond with one O atom of oxygenated diamond surface. All the oxygenated diamond surfaces with various adsorbates exhibit an electric insulativity.

Computation by Intention and Electronic Image of the Brain

Neurons as active unities are connected one with the others by synapses in an electronic way. We argue that brain is not comparable with digital computer with algorithms because intention as software is introduced as transformation in the neural states without any digital reduction. Any electronic system has voltages and currents sources and complex interconnected impedances. By electronic system and neural network we have different possibilities to introduce Freeman intentional transformation in the brain. One is to use source voltages (sensor) to generate wanted behavior of currents (internal flows of the signals) with the same impedance network. We can also reverse the process: given the behavior of the currents we generate wanted voltages transformation (effectors as muscles) with the same impedance. Another possibility is to change the impedance network (memory) to generate wanted internal current. When intention is transformation of references, geometry changes and also the form of straight line (geodesic). Special reference and geometry can be modeled by the electrical power as metric. Different types of brain geometries as hyperbolic geometry of waves and elliptic geometry of stable states are discussed with examples. Because we have waves in brain, Karl Pribram created holographic model of brain that by scattering and transmitted matrix can be joined to electronic model. Mechanical system metrics are implemented in the neural network as electronic network.

Стереохімія епоксидування біцикло[2.2.1]гепт-2-єнів та їх 7-syn-заміщених похідних. Дослідження методом DFT

The stereochemical aspects of epoxidation of norbornene and its 7- syn -substituted derivatives by performic acid were investigated. Geometry and thermodynamic parameters of transition states and prereactive complexes were computed at the UBHandHLYP/6-31G(d) level of theory. It is shown that the transition states have a pronounced biradical character and a nearly coplanar orientation of the C=C bond and the molecule of performic acid. Transition state analysis revealed that, in the case of the syn -7-hydroxy derivative, the preference for the exo -approach of the oxidant can be explained by the stabilization of transition state with hydrogen bonding. In contrast, a chlorine atom or a methyl group at the 7- syn position facilitated the formation of endo -epoxides due to steric repulsion between the substituent and the oxidant.

A quantitative geometric mechanics lens model: Insights into the mechanisms of accommodation and presbyopia

This study expands on a geometric model of ocular accommodation (Reilly and Ravi, Vision Res. 50:330-336; 2010) by relaxing assumptions regarding lens symmetry about the equator. A method for predicting stretching force was derived. Two models were then developed: Model 1 held the equatorial geometry constant at all stages of accommodation, while Model 2 allowed localized deformation at the equator. Both models were compared to recent data for axial thickness, anterior and posterior radii of curvature, surface area, cross-sectional area, volume, and stretching force for the 29-year-old lens. Age-related changes in accommodation were also simulated. Model 1 gave predictions which agreed with the Helmholtz theory of accommodation, while Model 2's predictions agreed with the Schachar mechanism of accommodation. Trends predicted by Model 1 agreed with all available experimental data, while Model 2 disagreed with recent surface area measurements. Further analysis indicated that Model 1 was fundamentally more efficient in that it required less force per diopter change in optical power than Model 2. Model 1 more accurately predicted age-related changes in accommodation amplitude. This implies that the zero-force (fully accommodated) state geometry changes with age due to a shifting balance in residual stresses between the lens and capsule.

Synthesis and structural elucidation of bioactive triorganotin(IV) derivatives of sodium deoxycholate

Trimethyl (1), tributyl (2), and triphenyl tin (3) derivatives of sodium (R)-4-((3R,5R,8R,9S,10S,12S,13R,14S,17R)-3,12-dihydroxy-10,13-dimethyl-hexadecahydro-1H-cyclopenta[a]phenanthren-17-yl)pentanoate (sodium deoxycholate) were synthesized by refluxing sodium deoxycholate with the corresponding triorganotin(IV) chloride in 1 : 1 M ratio. All the three compounds were characterized by elemental analysis, infrared spectroscopy, 1H, 13C, 119Sn NMR, and X-ray diffraction studies. From FT-IR spectra, Δν values proposed bridging or chelating behavior of the ligand. The three compounds gave a trigonal bipyramidal geometry in the solid state and tetrahedral geometry in solution. Single crystal of 1 showed polymeric trigonal bipyramidal geometry. Synthesized compounds obtained were screened for their antimicrobial and antitumor activities against A2780 cell line. Results revealed that only 2 showed significant antibacterial activity. However, all the three compounds exhibited promising antifungal and anticancer activities.

Theoretical studies of structures and spectroscopic properties of [(tpy)(bpy)RuC≡CC6H4R]+ (tpy = 2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine; R = F, Cl, H, Me and OMe)

A series of polypyridine ruthenium (II) acetylide complexes, [(tpy)(bpy)RuC≡CC6H4R]+ (tpy = 2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine; R = F (1), Cl (2), H (3), Me (4) and OMe (5)) are investigated theoretically to explore their electronic structures and spectroscopic properties. Their ground/excited state geometries, electronic structures and spectroscopic properties are first calculated using density functional theory (DFT) and time-dependent DFT (TDDFT). The absorption and emission spectra of the complexes in acetonitrile solution are also obtained by using TDDFT (B3LYP) method associated with the CPCM model. The calculations show that the energy levels of HOMOs for 1–5 are sensitive to the substituent on phenylacetylide ligand and increase with the same order of the electron-donating ability of the substituents; however, those of polypyridine-based LUMOs vary slightly. The lowest-energy absorptions and emissions for 1–5 are progressively red-shifted in the order of 1 ≈ 2 < 3 < 4 < 5 when the electron-donating groups are introduced into the phenylacetylide ligand. The phosphorescence of 1 are attributed to {[d xz (Ru) + π(C≡C)]→[π*(tpy)]} (3MLCT/3LLCT) transition, whereas those of 2–5 are originated from {[d xz /d xy (Ru)+π(C≡C)+π(C6H4R)]→[π*(tpy/bpy)]} (3MLCT/3LLCT) transitions.

Dynamical phase transitions, time-integrated observables, and geometry of states

We show that there exist dynamical phase transitions (DPTs), as defined by Heyl et al. [Phys. Rev. Lett. 110, 135704 (2013)], in the transverse-field Ising model (TFIM) away from the static quantum critical points. We study a class of special states associated with singularities in the generating functions of time-integrated observables as found by Hickey et al. [Phys. Rev. B 87, 184303 (2013)]. Studying the dynamics of these special states under the evolution of the TFIM Hamiltonian, we find temporal nonanalyticities in the initial-state return probability associated with dynamical phase transitions. By calculating the Berry phase and Chern number we show the set of special states have interesting geometric features similar to those associated with static quantum critical points.

The effect of donors–acceptors on the charge transfer properties and tuning of emitting color for thiophene, pyrimidine and oligoacene based compounds

We have designed 4,6-di(thiophen-2-yl)pyrimidine (DTP) derivatives with the aim to tune the electronic, optical and charge transport properties then predicted their properties of interests by applying the density functional theory and time dependent density functional theory. The anthracene has been substituted at both ends of the DTP with the aim to enhance the properties. The intra-molecular charge transfer (ICT) has been improved by substituting the electron-donating groups (EDGs) at one end while electron-withdrawing groups (EWDGs) at other end. We have conducted theoretical studies on the effect of EDGs (OH and OCH3), EWDGs (F, Cl, COOH, CN, NO2) and π-backbone on electronic, photophysical (absorption and emission), and charge transfer properties (ionization potentials, electron affinities and reorganization energies). The structure–properties relationship has been discussed. The ground (S0) and excited state (S1) state geometries have been optimized using DFT/B3LYP/6-31G** and TD-B3LYP/6-31G** level of theories, respectively. The comprehensible ICT has been observed from highest occupied molecular orbitals to lowest unoccupied molecular orbitals in new designed derivatives. The decreased injection barrier is revealing that new designed derivatives would be better charge transport materials than the parent molecule. Moreover, smaller hole reorganization energies of DTPBA_OH_Cl, and DTPBA_OH_F are revealing that these might be better/comparable to pentacene. The computed electron reorganization energies of new designed materials are smaller than that of well known and commonly used electron transport material (mer-Alq3) illuminating that the electron mobility of all the new designed derivatives might be better/comparable with mer-Alq3.

First-Principle Calculation of the Co Doped Anatase TiO&lt;sub&gt;2&lt;/sub&gt;

Using first-principle calculations based on density function theory (DFT), the geometry , band structure and electronic density of states of Co-doped anatase titanium dioxide (Co/TiO2) have been studied at plane wave ultra-soft pseudo-potential (PWPP). The states of the valence bands and conduction bands of pure and Co doped TiO2 with anatase structure were calculated. The density of states of pure anataseTiO2 and Co-doped TiO2 is analyzed in detail based on the calculations using the first-principles. From the calculated results, the band gaps of anataseTiO2 and Co doped TiO2 are about 2.15 and 0.78eV, respectively. It shows that Co doped anatase titanium dioxide may lead to the narrowing of the band gap in Co/TiO2. The Co doped anataseTiO2 could be a potential candidate for photocatalyst because it can enhance the photocatalytic activity of anatase TiO2.