Electronic Charge Density Distribution Research Articles

Estimating the Ground and Excited State Dipole Moments of Levofloxacin and Norfloxacin Drugs Using Solvatochromic Effects and Computational Work

Levofloxacin (LVF) and norfloxacin (NRF) are a group of fluoroquinolone antibiotics, broad spectrum used to treat various infections caused by many bacterial species. The drugs contain functional groups which control the type and degree of interaction with different solvents. In this research, the ground and excited state dipole moments of LVF and NRF drugs were estimated using solvatochromic effects and computational work. The dipole moments were estimated from absorption and emission spectra in polar and nonpolar solvents using Bakhshiev’s, Kawski–Chamma–Viallet, Lippert–Mataga, and Reichardt models. The results indicated the emission spectra are more strongly affected by solvent polarity than the absorption spectra. The calculated excited state dipole moment is larger than that of the ground state, indicating that the probe compounds are significantly more polarized in the excited state than in the ground state. From computational work, the HOMO-LUMO energy band gap, the dipole moments, electron charge density distribution, and oscillator strength were determined using the semiempirical MP6 method, DFT-B3LYP-6-31G, and DFT-B3LYP-3-21G employing Gaussian 09 software. In general, larger dipole moments were obtained by computation rather than from experiments due to the absence of solvent effects.

Structural and electronic properties of wide band gap charge transfer insulator Hg2Cl2: Insights from the first-principle calculations

The structural and electronic properties of Mercurous Chloride (Hg2Cl2) in its tetragonal (I4/mmm) phase at room temperature have been investigated from the first principle calculations. Detail calculations within the framework of density functional theory (DFT) upon incorporation of spin-orbit coupling (SOC) reveal that Hg2Cl2 is a wide band gap charge transfer (CT) insulator with band gap energy (Eg) ∼ 3.96 eV. Despite being a CT insulator, the orbital resolved PDOS of Hg2Cl2 compound exhibit energy dispositions that do not obey the Zaanen – Sawatzky – Allen (ZSA) diagram. The effect of on-site Coulomb repulsion (Hubbard +Udd) on the band gap of the compound has also been studied in detail. The Mulliken bond population, electronic charge density distribution and Bader charges analyses have been explored to unveil the covalent and ionic interactions between Hg and Cl atoms of the Hg2Cl2 compound. The Natural Bond Orbital (NBO) analyses have been performed to gain deeper insights on the CT interactions between Hg and Cl atoms of Hg2Cl2. The rationale behind the distortions of the octahedral domains within Hg2Cl2 crystal has also been elucidated in detail.

BASIC CONCEPTS IN PSYCHIATRIC GENETICS

We have performed spin-polarized calculation for the electronic band structure, density of states, Fermi surface and the space electronic charge density distribution for the filled-skutterudites LaFe4Pn12 (Pn=P, As and Sb) compounds. It has been noticed that for both LaFe4P12 and LaFe4As12 there are two bands cross Fermi level (EF) for the spin-up and spin-down states, while for LaFe4Sb12 there is only one band cross EF for the spin-up state and three bands cross EF for the spin-down state. As the partial DOS of La-s,d, Fe-s/p/d and Pn-s/p/d coincide Fermi level at nonzero value, it reveals that the electrons of these orbitals contribute in the conduction process. The calculated values of the density of the states at Fermi level N(EF) and the associated electronic specific heat coefficient (γ) for the spin-up/down states are decreases with substituting P→As→Sb. The bonds nature and the interactions between the atoms for the spin-up/down configurations were investigated in (1 0 0) and (1 0 1) crystallographic planes.

Calculation of vibrational frequencies, Energetic and some other Quantum Chemical Parameters for some Flavonoids

Computational study objective understanding the molecular factors that influence their structural design electronic charge density on atoms and energetic properties, using quantum mechanics calculations of the Semiempirical theory PM3 and Density Functional Theory DFT of (B3LYP) with a 6-311++G (2d, 2p) by using Gaussian-09 program on Selected Phytomedicines molecules, Flavon, Claflanone, and Hesperetin. They were chosen because of their unique chemical structure, which enabled researchers to assess the impact of functional groups on physical properties.Theoretical study for physical Properties, bond length, energies, vibration modes, charge density and Mechanical Properties by Quantum Mechanical Calculations for Phytomedicines molecules.Both IR absorption intensities and vibration frequencies of 3N-6 for all species were measured and allocated, and correlations for the frequencies of related modes were observed using the Herzberg convention. In addition to certain physical properties such as heat of formation, total energy, electronic charge density on atoms, dipole moment, and energy gap (E= ELUMO-EHOMO), the calculated physical properties and quantum chemical parameters correlated for the three Phytomedicines molecules. The distribution of electronic charge density on the atoms of three molecules was also measured and analyzed using the Gaussian 09 program; all three molecules were studied and discussed at their equilibrium geometry, symmetry..

Recrystallization Characteristics of Catalytic Alloy and Graphite in Diamond Synthesis

We first consider the recrystallization characteristics of catalysis alloy and graphite in the process of diamond synthesis under the condition of super high pressure and high temperature in catalysis method. In the process of diamond synthesis catalysis metal is plastically deformed by increase of pressure and then recrystallized as increasing the temperature. As catalysis metal is recrystallized, the shape of graphite particle is in spherical shape in the region contacting with the catalyst but in any shape in the opposite region. In addition, we calculate the electron charge density distribution and cohesive energies of cementite structure using the first principle method to investigate the reciprocal interaction between transient metal elements and carbon atoms in high-temperature catalyst synthesis. After determination of lattice constant parameters, we obtain the cohesive energy by subtracting the total energy of the crystal from the summation of total energies of atoms composing the crystal and dividing it by the number of atoms. Therefore, the effect of the catalyst on the diamond synthesis is to be analyzed theoretically.

Control of chirality, bond flexing and anharmonicity in an electric field

AbstractWe located “hidden” S‐character chirality in formally achiral glycine using a vector‐based interpretation of the total electronic charge density distribution. We induced the formation of stereoisomers in glycine by the application of an electric field. Control of chirality was indicated from the proportionate response to a non‐structurally distorting electric field. The bond‐flexing was determined to be a measure of bond strain, which could be a factor of three lower or higher, depending on the direction of the electric field, than in the absence of the electric field. The bond‐anharmonicity was found to be approximately independent of the electric field. We also compared the formally achiral glycine with the chiral molecules alanine and lactic acid, quantifying the preferences for the S and R stereoisomers. The proportional response of the chiral discrimination to the magnitude and direction of the applied electric field indicated use of the chirality discrimination as a molecular similarity measure.

A comprehensive DFT based insights into the physical properties of tetragonal superconducting Mo5PB2

Tetragonal Mo5PB2, a recently discovered superconductor, is an extension of transition metal binaries with general formula T5M3. A large number of physical properties of Mo5PB2, including elastic properties and their anisotropy, acoustic behavior, electronic (charge density distribution, electron density difference), thermophysical, bonding characteristics, and optical properties have not been carried out at all till date. In this work, all these properties have been studied in details for the first time employing density functional theory based first-principles method. Mo5PB2 is found to be a mechanically stable, elastically anisotropic compound with ductile character. Chemical bonding characteristics are understood from electronic energy density of states, electron density distribution, elastic properties and Mulliken and Hirshfeld bond population analyses. Mo5PB2 has a combination of ionic, metallic, and covalent bondings. Mo5PB2 possesses high level of machinability. Large electronic density of states at the Fermi level, N(EF), reveals its metallic character. High value of N(EF) facilates superconductivity. Calculated values of different thermal parameters of Mo5PB2 are closely related to the elastic moduli and constants. Energy dependent optical parameters show close agreement to the underlying electronic band structure. The optical absorption and reflectivity spectra and the low energy index of refraction of Mo5PB2 disclose its promise to be used in the optoelectronic device sector. Unlike the notable anisotropy found in elastic properties and minimum thermal conductivity, the optical parameters are found to be almost isotropic with respect to the polarization direction of the electric field.

First-principles calculation of the electronic and optical properties of Gd2FeCrO6 double perovskite: Effect of Hubbard U parameter

We have synthesized Gd$_{2}$FeCrO$_{6}$ (GFCO) double perovskite which is crystallized in a monoclinic structure with P2$_{1}/$n space group. The UV-visible and photoluminescence spectroscopic analyses confirmed its direct bandgap semiconducting nature. Employing experimentally obtained structural parameters in first-principles calculation, we report the spin-polarized electronic band structure, charge carrier effective mass, density of states, electronic charge density distribution and optical absorption property of the GFCO double perovskite. The effects of on-site d-d Coulomb interaction energy (U$_{eff}$) on the electronic and optical properties were investigated by applying a range of Hubbard U$_{eff}$ parameters from 0 to 6 eV to the Fe-3d and Cr-3d orbitals within the generalized gradient approximation (GGA) and GGA+U methods. When we applied U$_{eff}$ in the range of 1 to 5 eV, both the up-spin and down-spin band structures were observed to be direct. The charge carrier effective masses were also found to enhance gradually from U$_{eff} =$ 1 eV to 5 eV, but, these values were anomalous for U$_{eff} =$ 0 and 6 eV. These results suggest that U$_{eff}$ should be limited within the range of 1 to 5 eV to calculate the structural, electronic and optical properties of GFCO double perovskite. We observed that considering U$_{eff} =$ 3 eV, the theoretically calculated optical band gap 1.99 eV matched well with the experimentally obtained value 2.0 eV. The outcomes of our finding imply that the U$_{eff}$ value of 3 eV most accurately localized the Fe-3d and Cr-3d orbitals of GFCO keeping the effect of self-interaction error from the other orbitals almost negligible. Therefore, we may recommend U$_{eff} =$ 3 eV for first-principles calculation of the electronic and optical properties of GFCO double perovskite that might have potential in photocatalytic and related solar energy applications.

A dimeric chlorophyll electron acceptor differentiates type I from type II photosynthetic reaction centers

SummaryThis research addresses one of the most compelling issues in the field of photosynthesis, namely, the role of the accessory chlorophyll molecules in primary charge separation. Using a combination of empirical and computational methods, we demonstrate that the primary acceptor of photosystem (PS) I is a dimer of accessory and secondary chlorophyll molecules, Chl2A and Chl3A, with an asymmetric electron charge density distribution. The incorporation of highly coupled donors and acceptors in PS I allows for extensive delocalization that prolongs the lifetime of the charge-separated state, providing for high quantum efficiency. The discovery of this motif has widespread implications ranging from the evolution of naturally occurring reaction centers to the development of a new generation of highly efficient artificial photosynthetic systems.Video abstract

A DFT based first-principles investigation of optoelectronic and structural properties of Bi2Te2Se

Bi2Te2Se is a topological insulator (TI) having conducting surface electronic states with an energy gap in the bulk electronic band structure. Such systems are promising for variety of superconducting and quantum computation related applications. In addition, TIs may possess other important bulk physical characteristics appropriate for more conventional applications which are not affected significantly by spin–orbit interaction. In this study we focus on bulk properties of Bi2Te2Se which are not greatly affected by the surface electronic states and therefore, by spin–orbit coupling. We have investigated elastic, mechanical, electronic, optical properties, bonding character and the electronic charge density distribution of ternary Bi2Te2Se to explore its feasibility for potential applications. Bi2Te2Se is found to be mechanically stable and elastically anisotropic. Electronic effective mass is high in the c-direction compared to that in the ab-plane. The optical constants show moderate level of variation with respect to the polarization of the electric field of the incident radiation. The optical spectra are consistent with the bulk electronic band structure and electronic density of states features. Both electronic band structure and optical constants show clear indications of a direct band gap of 0.61 eV for Bi2Te2Se. Bi2Te2Se possesses high refractive index at low photon energies in the infrared and visible region. It has low reflectivity in the ultraviolet region. Bi2Te2Se absorbs photons strongly in the ultraviolet energies. All these characteristics make Bi2Te2Se suitable for diverse class of optoelectronic device applications.

La induced Si3 trimer bilayer on the Si(111) surface.

Using first-principles calculations, we identify a robust R30° reconstruction of a Si3 trimer bilayer on the Si(111) surface with a La coverage of 2/3 monolayer. Each surface unit cell contains two Si3 trimers and two La atoms, where the upper Si3 trimer is located just above the lower one with a rotation of about 60°, while two La atoms with different heights are distributed between the Si3 trimers and located on the T4 top site of the Si(111) surface, forming a honeycomb-like network structure. We find that the two La atoms have different valence states, La2+ and La3+, respectively. The high structural stability is attributed to the lower La atom saturating all the three dangling bonds of the upper Si3 trimer, while the higher La atom compensates two electrons to the lower Si3 trimer. The electronic band structure and band-decomposed charge density distribution show a semiconducting characteristic with a small surface band gap of 42 meV. Moreover, simulated STM images show a good structural match with the recent experimental observations.

Nonparametric Local Pseudopotentials with Machine Learning: A Tin Pseudopotential Built Using Gaussian Process Regression

We present novel nonparametric representation math for local pseudopotentials (PP) based on Gaussian Process Regression (GPR). Local pseudopotentials are needed for materials simulations using Orbital-Free Density Functional Theory (OF-DFT) to reduce computational cost and to allow kinetic energy functional (KEF) application only to the valence density. Moreover, local PPs are important for the development of accurate KEFs for OF-DFT, but they are only available for a limited number of elements. We optimize local PPs of tin (Sn) represented with GPR to reproduce the experimental lattice constants of α- and β-Sn and the energy difference between these two phases as well as their electronic structure and charge density distributions which are obtained with Kohn-Sham Density Functional Theory employing semilocal PPs. The use of a nonparametric GPR-based PP representation avoids difficulties associated with the use of parametrized functions and has the potential to construct an optimal local PP independent of prior assumptions. The GPR-based Sn local PP results in well-reproduced bulk properties of α- and β-tin and electronic valence densities similar to those obtained with semilocal PP.

Structural Insight of the Frailty of 2D Janus NbSeTe as an Active Photocatalyst

AbstractA new family of 2D materials, Janus MTeSe (M=Nb, Mo, or W) pristine and defective monolayers have been investigated in this work as promising catalysts for hydrogen evolution reaction (HER) based on first‐principles calculations. It has been observed that these Janus monolayers are dynamically and thermodynamically stable. Hybrid exchange‐correlation functional (HSE06) based electronic structures reveal Janus NbTeSe is a polarized semiconductor with an indirect bandgap of 1.478 eV with excellent optical absorption capability near infra‐red region. While MoTeSe and WTeSe monolayers are direct bandgap semiconductors with a suitable bandgap of 1.859 and 1.898 eV. The carrier effective masses and mobilities in MTeSe monolayer are also calculated. Subsequently, the catalytic activity of pristine as well as defective MTeSe for HER has been identified from the reaction coordinate based on the adsorption free energy ( ). It is noticed that the Nb based Janus layer has comparatively weak HER activity than its peers, group VIB transition metals, Mo, W based Janus layer. The Coulomb attraction between the hydrogen and the monolayer decreases with the increase of the inner atomic radius from Nb, Mo to W, which is one of the structural frailties of 2D Janus NbSeTe as an active photocatalyst. We have further analyzed electronic structures and charge density distributions of pristine and defective MTeSe with/without H adatom to unveil the reason of the catalytic inferiority for Nb based Janus layer over W and Mo based systems. This comparative study of Janus MTeSe monolayers with HSE06 would provide a deep understanding of Janus based HER catalyst.

Charge order of bismuth ions and nature of chemical bonds in double perovskite-type oxide BaBiO3 visualized by synchrotron radiation X-ray diffraction

Synchrotron radiation X-ray powder diffraction has visualized the charge order of Bi3+ and Bi5+ ions and the nature of chemical bonds in BaBiO3 in electron charge density distribution maps. The Bi3+–O bond is considerably more ionic than the Bi5+–O bond in all four phases. BaBiO3 can be regarded as an ionic crystal in the prototype structure comprising isolated Ba2+ and Bi3+ ions as well as [Bi5+O6]7− octahedra in the Fmm symmetry; a three-dimensional covalent bonding network is formed in the R and I2/m symmetries, and a two-dimensional layered structure comprising Bi3+O4 planar squares and Bi5+O6 octahedra is established in the P21/n symmetry at low temperatures. Our study provides a comprehensive understanding of the structural characteristics, electron charge density distribution, and chemical bonds of BaBiO3, which may be useful for developing BaBiO3-based functional materials such as superconductors.

CO2 Electrochemical Reduction by Exohedral N-Pyridine Decorated Metal-Free Carbon Nanotubes

Electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals represents nowadays one of the most challenging solutions for renewable energy storage and utilization. Among the possible reaction pathways, CO2-to-CO conversion is the first (2e−) reduction step towards the production of a key-feedstock that holds great relevance for chemical industry. In this report we describe the electrocatalytic CO2-to-CO reduction by a series of tailored N-decorated carbon nanotubes to be employed as chemoselective metal-free electrocatalysts. The choice of an exohedral functionalization tool for the introduction of defined N-groups at the outer surface of carbon nanomaterials warrants a unique control on N-configuration and electronic charge density distribution at the dangling heterocycles. A comparative electrochemical screening of variably N-substituted carbon nanomaterials in CO2RR together with an analysis of the electronic charge density distribution at each heterocycle have suggested the existence of a coherent descriptor for the catalyst’s CO faradaic efficiency (FECO). Evidence allows to infer that N-configuration (N-pyridinic vs. N-pyrrolic) of exohedral dopants and electronic charge density distribution at the N-neighboring carbon atoms of each heterocycle are directly engaged in the activation and stabilization of CO2 and its reduction intermediates.

A charge density prediction model for hydrocarbons using deep neural networks

The electronic charge density distribution ρ(r) of a given material is among the most fundamental quantities in quantum simulations from which many large scale properties and observables can be calculated. Conventionally, ρ(r) is obtained using Kohn–Sham density functional theory (KS-DFT) based methods. But, the high computational cost of KS-DFT renders it intractable for systems involving thousands/millions of atoms. Thus, recently there has been efforts to bypass expensive KS equations, and directly predict ρ(r) using machine learning (ML) based methods. Here, we build upon one such scheme to create a robust and reliable ρ(r) prediction model for a diverse set of hydrocarbons, involving huge chemical and morphological complexity /(saturated, unsaturated molecules, cyclo-groups and amorphous and semi-crystalline polymers). We utilize a grid-based fingerprint to capture the atomic neighborhood around an arbitrary point in space, and map it to the reference ρ(r) obtained from standard DFT calculations at that point. Owing to the grid-based learning, dataset sizes exceed billions of points, which is trained using deep neural networks in conjunction with a incremental learning based approach. The accuracy and transferability of the ML approach is demonstrated on not only a diverse test set, but also on a completely unseen system of polystyrene under different strains. Finally, we note that the general approach adopted here could be easily extended to other material systems, and can be used for quick and accurate determination of ρ(r) for DFT charge density initialization, computing dipole or quadrupole, and other observables for which reliable density functional are known.

Electronic and optical properties of Tl4GeX3 (X = S, Se and Te) compounds for optoelectronics applications: insights from DFT-computations

In this work, first-principles computational study on the structural, electronic and optical properties of Tl4GeS3, Tl4GeSe3 and Tl4GeTe3 ternary compounds are presented. The computations are performed with pseudopotential plane wave method based on density functional theory with the generalized gradient approximation of Perdew–Burke and Enzerhof (PBE-GGA). The calculated structural, electronic and optical parameters are consistent with the available experimental results. The computed electronic band structures confirm the semiconducting nature for these compounds with direct band gaps of 0.17eV, 0.085eV and 0.015eV for Tl4GeS3, Tl4GeSe3 and Tl4GeTe3, respectively. Furthermore, the electron charge density distribution indicated that the nature of bonds between Ge and S/Se/Te are covalent nature, whereas Ge and S/Se/Te anions formed ionic bonds. The optical parameters revealed that Tl4GeS3, Tl4GeSe3 and Tl4GeTe3 are highly dielectric materials and has the potential to be beneficial in the optoelectronic device applications.

Predicting charge density distribution of materials using a local-environment-based graph convolutional network

Electron charge density distribution of materials is one of the key quantities in computational materials science as theoretically it determines the ground state energy and practically it is used in many materials analyses. However, the scaling of density functional theory calculations with number of atoms limits the usage of charge-density-based calculations and analyses. Here we introduce a machine learning scheme with local-environment-based graphs and graph convolutional neural networks to predict charge density on grid-points from crystal structure. We show the accuracy of this scheme through a comparison of predicted charge densities as well as properties derived from the charge density, and the scaling is O(N). More importantly, the transferability is shown to be high with respect to different compositions and structures, which results from the explicit encoding of geometry.

Fermi level shift in carbon nanotubes by dye confinement

Dye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system.

Crystallographic orientation dependence of work function: carbon adsorption on Au surfaces

We investigate the work function (WF) variation of different Au crystallographic surface orientations with carbon atom adsorption. Ab initio calculations within density-functional theory are performed on carbon deposited (100), (110), and (111) gold surfaces. The WF behaviour with carbon coverage for the different surface orientations is explained by the resultant electron charge density distributions. The dynamics of carbon adsorption at sub-to-one- monolayer (ML) coverage depends on the landscape of the potential energy surfaces. At higher ML coverage, because of adsorption saturation, the WF will have weak surface orientation dependence. This systematic study has consequential bearing on studies of electric-field noise emanating from polycrystalline gold ion-trap electrodes that have been largely employed in microfabricated electrodes.