Ground State Electronic Properties Research Articles

Ground state structures, electronic and optical properties of medium-sized Nan + (n = 9, 15, 21, 26, 31, 36, 41, 50 and 59) clusters from ab initio genetic algorithm

Employing genetic algorithm incorporated with density functional theory calculations we determined the lowest-energy structures of cationic Na n + clusters (n = 9, 15, 21, 26, 31, 36, 41, 50 and 59). We revealed a transition of growth pattern from “polyicosahedral” sequence to the Mackay icosahedral motif at around n = 40. Based on the ground-state structures the size dependent electronic properties of Na n + clusters including the binding energies, HOMO-LUMO gaps, electron density of states and photoabsorption spectra were discussed. As cluster size increases, the HOMO-LUMO gap of Na n + cluster gradually reduces and converges to metallic behavior of bulk crystal rapidly. The photoabsorption spectra of Na n + clusters from our calculations agree with experimental data rather well, confirming the reliability of our theoretical approaches.

Electronic Structure and Ground State Properties of A<sub>4</sub>[Ag<sub>4</sub>O<sub>4</sub>] (A=Na, K and Rb): A First-Principles Study

The first-principles calculation within density functional theory is used to study in detail the electronic structure and ground state properties of alkali-metal oxoargenates A4[Ag4O4] (A= Na, K and Rb). The total energies calculated within the atomic sphere approximation (ASA) were used to determine the ground state properties such as equilibrium lattice parameter, c/a ratio, bulk modulus and cohesive energy. The theoretically calculated equilibrium lattice constants values are in well agreement with the available experimental values. The electronic band structures, total and partial density of states are calculated. The result of electronic band structure shows that the KAgO and RbAgO are direct band gap semiconductors with their gap lying between the Γ-Γ points, whereas NaAgO is found to be an indirect band gap semiconductor with its gap lying between Z-Γ points.

Density-Functional Theory Study on Neutral and Charged M n C2 (M = Fe, Co, Ni, Cu; n = 1–5) Clusters

The ground-state geometrical and electronic properties of neutral and charged M n C2 (M = Fe, Co, Ni, Cu; n = 1–5) clusters are systematically investigated by density-functional calculations. The growth evolution trends of neutral and charged Fe n C2, Co n C2, Ni n C2 and Cu n C2 (n = 1–5) clusters are all from lower to higher dimensionality, while it is special for Cu n C 2 ± (n = 1–5) clusters which favor planer growth model. The space directional distributions of Co and Ni indicate stronger magnetic anisotropy than that in Cu atoms. Compare with experimental data (photoelectron spectroscopy), our results are in good agreement. The interaction strengths between metal and carbon atoms in TM–C (TM = Fe, Co, Ni) clusters are comparable and are obviously larger than that in Cu–C clusters, and this interaction strengths also decrease through the sequence: cation > neutral > anion, which may be crucial in exploring the differences in the growth mechanisms of metal–carbon nano-materials.

Electron correlation and spin-orbit coupling effects in US3 and USe3

A systematic density functional theory (DFT)+U study is conducted to investigate the electron correlation and spin-orbit coupling (SOC) effects in US(3) and USe(3). Our calculations reveal that inclusion of the U term is essential to get energy band gaps for them, indicating the strong correlation effects for uranium 5f electrons. Taking consideration of the SOC effect results in small reduction on the electronic band gaps of US(3) and USe(3), but largely changes the energy band shapes around the Fermi energy. As a result, US(3) has a direct band gap while USe(3) has an indirect one. Our calculations predict that both US(3) and USe(3) are antiferromagnetic insulators, in agreement with corresponding experimental results. Based on our DFT+U calculations, we systematically present the ground-state electronic, mechanical, and Raman properties for US(3) and USe(3).

Ground State Electronic and Magnetic Properties of LaCrO<sub>3</sub> System

First principle calculations are carried out to investigate the ground state electronic and magnetic properties of G-type antiferromagnetic (AFM) LaCrO3 compound in orthorhombic phase. The orthorhombic LaCrO3, a distorted GdFeO3 – type perovskite exhibits AFM transition at ~290 K. Additionally; this system shows weak ferromagnetism at room temperature, in conjugation with its semiconducting properties. In this paper, we will discuss the onset of weak ferromagnetism and electronic properties of LaCrO3, implementing generalized gradient approximation for exchange correlation potential. We present results for electronic structure and density of states, including the effect of onsite Coulomb interaction and non-collinear arrangement of Cr3+ magnetic ions in G-type AFM geometry.

Electronic ground-state properties of strained graphene

We consider the effect of the Coulomb interaction in strained graphene using tight-binding approximation together with the Hartree-Fock interactions. The many-body energy dispersion relation, anisotropic Fermi velocity renormalization and charge compressibility in the presence of uniaxial strain are calculated. We show that the quasiparticle quantities are sensitive to homogenous strain and indeed, to its sign. The charge compressibility is enhanced by stretching and suppressed by compressing a graphene sheet. We find a reduction of Fermi velocity renormalization along the direction of graphene deformation, in good agreement with the recent experimental observation.

Multiple scattering theory for non-local and multichannel potentials

Methodological advances in multiple scattering theory (MST) in both wave and Green’s function versions are reported for the calculation of electronic ground and excited state properties of condensed matter systems with an emphasis on core-level photoemission and absorption spectra. Full-potential MST is reviewed and extended to non-local potentials. Multichannel MST is reformulated in terms of the multichannel density matrix whereby strong electron correlation of atomic multiplet type can be accounted for in both ground and excited states.

Time-Resolved Vibrational Spectroscopy of [FeFe]-Hydrogenase Model Compounds

Model compounds have been found to structurally mimic the catalytic hydrogen-producing active site of Fe-Fe hydrogenases and are being explored as functional models. The time-dependent behavior of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) and Fe(2)(μ-S(2)C(2)H(4))(CO)(6) is reviewed and new ultrafast UV- and visible-excitation/IR-probe measurements of the carbonyl stretching region are presented. Ground-state and excited-state electronic and vibrational properties of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) were studied with density functional theory (DFT) calculations. For Fe(2)(μ-S(2)C(3)H(6))(CO)(6) excited with 266 nm, long-lived signals (τ = 3.7 ± 0.26 μs) are assigned to loss of a CO ligand. For 355 and 532 nm excitation, short-lived (τ = 150 ± 17 ps) bands are observed in addition to CO-loss product. Short-lived transient absorption intensities are smaller for 355 nm and much larger for 532 nm excitation and are assigned to a short-lived photoproduct resulting from excited electronic state structural reorganization of the Fe-Fe bond. Because these molecules are tethered by bridging disulfur ligands, this extended di-iron bond relaxes during the excited state decay. Interestingly, and perhaps fortuitously, the time-dependent DFT-optimized exited-state geometry of Fe(2)(μ-S(2)C(3)H(6))(CO)(6) with a semibridging CO is reminiscent of the geometry of the Fe(2)S(2) subcluster of the active site observed in Fe-Fe hydrogenase X-ray crystal structures. We suggest these wavelength-dependent excitation dynamics could significantly alter potential mechanisms for light-driven catalysis.

Theoretical study of the Pu and Am dicarbide molecules

The electronic structure and ground-state molecular properties of Pu and Am dicarbides were investigated in this study by relativistic multireference calculations using CASSCF/CASPT2 theory. The electronic ground states in both the molecules correspond to a symmetrical triangular structure, in which the actinide atom is connected to a C2 moiety. The other experimentally relevant structure, the symmetrical linear arrangement, is higher than 100 kJ/mol in energy. The bonding characteristics in the two structures were analysed on the basis of the valence molecular orbitals. Besides the usual two-electron bonds, a few one-electron bonding orbitals were also identified. We evaluated the electronic spectra with complete active space state interaction (CASSI) calculations taking into account spin–orbit coupling. The infrared and Raman spectral characteristics were obtained using DFT calculations. Assessment of the present results with the previously reported data on Th and U dicarbides provides information on the change of various molecular parameters in the actinide row.

Electronic, magnetic and dielectric properties of multiferroic MnTiO3

Abstract

Ground State Structures, Electronic and Magnetic Properties of ScnFe (n=2–10) Clusters

AbstractThe authors predict that the magnetic moment of the scandium clusters can not be efficiently enhanced with the encapsulation of Fe atom, which is different from previous works with Fe atom doped in Bn, Sin, and Gen clusters. It was found that starting from n=6, the growth patterns of the ground state structures of the ScnFe clusters are dominated by the octahedron structures with Fe atom falling into the center of the host framework. The calculated results manifest that doping of the Fe atom contributes to strengthening the stabilities of the scandium framework. Maximum peaks are observed for clusters of n=3, 6 and 8 on the size dependence of the second‐order energy differences, implying that these clusters possess relatively higher stability. The HOMO‐LUMO gap of the ScnFe clusters exhibits an oscillational odd‐even character with the local peaks of n=4, 6 and 8. Especially, there is the largest oscillation of the gap with n=4 and 5. Additionally, the doped Fe atom exhibits the antiferromagnetic alignment at n=4, 5, 7 and 9. Also, the quench of the magnetic moments as n=6, 8 and 10 may be ascribed to the model of close‐shell electrons.

Ab initio study of the properties of CuAlSe2: A chalcopyrite compound

Abstract The ground-state structural, electronic, optical and thermal properties of CuAlSe2 compound in the body centered tetragonal phase have been studied by employing the full potential linearized augmented plane wave plus local orbitals method based on the density functional theory. For the exchange-correlation effects we have adopted the local density approximation (LDA), generalized gradient approximation (GGA) due to Perdew, Burke and Ernzerhof (PBE) and Engel and Vosko (EV). At the equilibrium unit cell volume, ration of the lattice constants, c/a, has been obtained as 1.99 and the unit cell constant a 0 = 5.51Å which are well comparable with the experimental results. The energy band gap obtained using EVGGA (1.92 eV) is in good agreement in comparison to that using LDA (1.09 eV), GGA (PBE) (1.26 eV) and other earlier available data. Upper portion of the valance band is mainly composed of Cu-d and Se-p states and they are highly hybridized. The optical properties such as dielectric function, refraction, reflection, conductivity, absorption and loss of energy of CuAlSe2 are presented. The quasi Harmonic Debye model is applied to study the thermal and vibrational effects for the stable BCT CuAlSe2. Thermal parameters such as Gruneisen parameter, Debye temperature, specific heat etc have been determined as a function of pressure and temperature.

Application of a computational model for Michael addition reactivity in the prediction of toxicity to Tetrahymena pyriformis

A computational model to predict acute aquatic toxicity to the ciliate Tetrahymena pyriformis has been developed. A general prediction of toxicity can be based on three consecutive steps: 1. Identification of a potential reactive mechanism via structural alerts; 2. Confirmation and quantification of (bio)chemical reactivity; 3. Establishing a relationship between calculated reactivity and toxicity. The method described herein uses a combination of a reactive toxicity (RT) model, including computed kinetic rate constants for adduct formation (log k) via a Michael acceptor mechanism of action, and baseline toxicity (BT), modelled by hydrophobicity (octanol–water partition coefficient). The maximum of the RT and BT values defines acute toxicity for a particular compound. The reactive toxicity model is based on site-specific steric and quantum chemical ground state electronic properties. The performance of the model was examined in terms of predicting the toxicity of 106 potential Michael acceptor compounds covering several classes of compounds (aldehydes, ketones, esters, heterocycles). The advantages of the computational method are described. The method allows for a closer and more transparent mechanistic insight into the molecular initiating events of toxicological endpoints.

On the Stability, Electronic Structure, and Nonlinear Optical Properties of HXeOXeF and FXeOXeF

The electronic ground state, stability, and linear and nonlinear optical properties of HXeOXeF and FXeOXeF have been studied theoretically by employing complete active space valence bond (CASVB), multistate complete active space perturbation theory (MS-CASPT2), and coupled cluster methods. It is shown that the oxygen inserted between the two Xe atoms significantly modifies the ground-state electronic configuration of the formed derivative by increasing the closed-shell contribution (σ(2)) and removing the diradicaloid character observed in HXe(2)F. The electronic charge distribution has been analyzed by employing the atoms-in-molecules (AIM) method. The dissociation channels of HXeOXeF and FXeOXeF have been studied in detail. It was found that these compounds are metastable, protected by substantial energy barriers and, thus, they can be prepared under appropriate conditions. Both two- and three-body dissociation reactions have been considered. The effects of inserting O in HXe(2)F and substituting H (HXeOXeF) by F, leading to FXeOXeF, on the energy barriers are discussed. The significant effects of the inserted oxygen on the polarizability and even more on the first hyperpolarizability have been computed and rationalized.

Ground state electronic and magnetic properties of RCrSb 3 (R=La, Ce, Nd, Gd and Dy): A first principles study

The electronic density of states (DOS) and magnetic moments of rare-earth antimonides (RCrSb 3) have been studied by the first principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). For the exchange–correlation potential, the LSDA+U method is used. The effective moments of LaCrSb 3, CeCrSb 3, NdCrSb 3, GdCrSb 3, and DyCrSb 3 were found to be 3.03 μ B , 3.73 μ B , 5.77 μ B , 8.27 μ B and 4.69 μ B respectively. The exchange-splittings of Cr-3d state electrons and 4f-states of rare earth elements were analyzed to explain the magnetic nature of these systems. The Cr atom plays a significant role on the magnetic properties due to the hybridization between Cr-3d and Sb-5p state orbitals. The results obtained are compared and found to be in close agreement with the available data.

Electronic structure of fluorides: general trends for ground and excited state properties

The electronic structure of fluorite crystals are studied by means of density functional theory within the local density approximation for the exchange correlation energy. The ground-state electronic properties, which have been calculated for the cubic structures CaF2, SrF2, BaF2, CdF2, HgF2, β-PbF2, using a plane waves expansion of the wave functions, show good comparison with existing experimental data and previous theoretical results. The electronic density of states at the gap region for all the compounds and their energy-band structure have been calculated and compared with the existing data in the literature. General trends for the ground-state parameters, the electronic energy-bands and transition energies for all the fluorides considered are given and discussed in details. Moreover, for the first time results for HgF2 have been presented.

Ab initio studies of structural, electronic, optical and thermal properties of CuAlS 2 chalcopyrite

The ground-state structural, electronic, optical and thermal properties of the CuAlS 2 compound in the body centered tetragonal phase have been studied employing the full potential linearized augmented plane wave plus local orbitals method based on the density functional theory. For the exchange–correlation effects we have adopted the generalized gradient approximation (GGA) approaches due to Perdew, Burke and Ernzerhof (PBE) and Engel and Vosko (EV). The optical properties such as dielectric function, loss of energy, reflection, refraction and conductivity of CuAlS 2 are presented. Thermal properties such as Gruneisen parameter, volume expansion coefficient α, bulk modulus, specific heat and entropy have been studied. The direct band gap first increases then starts decreasing with the decrease in unit cell volume. The EV–GGA provides higher value of energy band gap (2.20 eV) than PBE–GGA (1.62 eV). Our obtained value of the refractive index (2.4 eV) is in excellent agreement with the experimental value (2.0–2.5 eV). The peak of maximum conductivity is located at 7.4 eV of energy. The plasma frequency ω p corresponds to the energy 12.45 eV.

Electronic Structure of some A3 Adenosine-Receptor Antagonist——A Structure Activity Relationship

DFT quantum chemical computations have been carried out at the B3LYP/6-31G (d) level. Full geometry optimization has been performed and equilibrium geometries for a new series of phenyl thiazoles have been located. Ground state electronic properties, charge density distributions, dipole moments and its components have been calculated and reported. Effect of substituents on the geometry and on the polarization of the studied series of compounds are analyzed and discussed. Some structural features have been pinpointed to underline the affinity and selectivity of the studied compounds as adenosine A3-receptor antagonists. Results of the present work indicate that activity towards A3 receptor sites is directly correlated with both of the polarity and the co-planarity of the thiazole.

Pu Electronic Structure and Photoelectron Spectroscopy

The electronic structure of PuCoGa5, Pu metal, and PuO2 is explored using photoelectron spectroscopy. Ground state electronic properties are inferred from temperature dependent photoemission near the Fermi energy for Pu metal. Angle-resolved photoemission details the energy vs. crystal momentum landscape near the Fermi energy for PuCoGa5 which shows significant dispersion in the quasiparticle peak near the Fermi energy. For the Mott insulators AnO2(An = U, Pu) the photoemission results are compared against hybrid functional calculations and the model prediction of a crossover from ionic to covalent bonding is found to be reasonable.

Theoretical Investigations of Ti-Based Binary Shape Memory Alloys

The electronic structure and ground state properties of TiX (X = Fe, Ni, Pd, Pt and Cu) type Shape Memory alloys have been calculated using the self consistent Tight- Binding Linear Muffin Tin Orbital (TB-LMTO) method. The systematic total energy studies made on TiX alloys in both B2 and (B19/B19’) structures successfully explain the structural stability of these compounds. The equilibrium lattice parameters, bulk moduli (Bo), cohesive energy (Ecoh) and heat of formation (ΔH) are calculated for these systems and compared with the available experimental and other theoretical results. The bonding nature of these TiX alloys is analyzed via the density of states (DOS) histogram.