Partial Electron Density Research Articles

First-principles studies on electronic structures of superatomic compounds [Co6Se8(PMe3)6][C60] in several cubic structures

Structural features, electronic structures, and optical properties of superatomic compounds [Co6Se8(PMe3)6][C60] with rock-salt, cesium chloride, and zinc-blende structures were investigated from first principles. Partial electronic density of states, highest occupied molecular orbital, and lowest unoccupied molecular orbital were given and used to discuss the detailed electronic structures. Dielectric function, refractive index, reflectivity, absorption coefficient, and energy loss functions under several pressures were calculated and used to investigate the optical properties. We found that Co6Se8(PMe3)6 transfers electrons and C60 receives electrons, making contributions to electron communications between the positive and negative counterparts on the basis of electrostatic interactions. The superatomic structures are made from assemblies of charge-rich and charge-poor molecular precursors. In the solid state, charge is transferred between the components, with a net reduction of C60 by less than one electron (0.75 electron approximately).

Structural, elastic, electronic, andoptical properties of layered TiNX (X = F, Cl, Br, I) compounds: a density functional theory study

ABSTRACTTitanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature. We have revisited the electronic band structure of TiNX using density functional theory (DFT) based calculations. The atomic orbital resolved partial electronic energy densities of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for the first time. The elastic anisotropy has been explored. The optical properties of TiNX are studied for the first time. The Debye temperatures have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and showed fair agreement. TiNX are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.

An ab-initio investigation of the electronic structure, chemical bonding and optical properties of Ba2HgS5 semiconductor

In this manuscript, the electronic structure, bonding nature and optical properties of the ternary Ba2HgS5 compound was investigated using the density functional theory (DFT). The generalised gradient approximation (GGA), Engel and Vosko generalised gradient approximation (EV-GGA) and the modified Becke Johnson (mBJ) schemes were used to model the exchange and correlation potentials. Band structure calculations indicate that this compound has a direct energy band gap value of 2.34 eV, showing a close agreement with the experimental band gap value of 2.40 eV. The energy band gap value calculated using the mBJ formalism is larger than those obtained from the GGA and the EV-GGA approaches. From the analysis of the partial electronic energy density of states, it was observed that the valence band is dominated by the Ba-p, S-s and Hg-d electronic states, while the conduction band is formed by the S-p and Ba-d orbitals. In addition, there exists a strong hybridisation in the valance band and in the conduction band between the S-p and Hg-s, Ba-s and Hg-f, Hg-s, S-p as well as the S-p and Hg-p states, respectively. This strong hybridisation leads to strong covalent bonding between the Hg-S and Ba-S atoms. Moreover, the optical constants were calculated and discussed in details. The energy dependent optical parameters were found to be anisotropic with respect to the polarisation of the incident electromagnetic wave and exhibit features in complete agreement with the electronic band structure calculations. The compound absorbs ultraviolet radiation quite strongly. Ba2HgS5 possesses high refractive index over a wide range of frequency and has potential to be used as anti-reflective coating and also in photonic devices like in light emitting diodes (LEDs).

Hydrogen and deuterium adsorption on uranium decorated graphene nanosheets: A combined molecular dynamics and density functional theory study

In this study, the combined density functional theory (DFT) and molecular dynamics (MD) simulation methods were carried out to investigate the potential capability of uranium-decorated graphene (U–G) for the separation of deuterium from hydrogen gases. Graphene with hexagonal honeycomb lattice arrangement is suitable for adsorption of individual uranium atoms, with a high binding energy (−1.173 eV) and U-U distance longer than 7 Å. This U-G system has ability to hold up to six H2 (5.16% wt) or seven D2 (11.75% wt) molecules per U atoms. To gain further insights into these interactions, partial electronic density of states (PDOS) and the electron density distribution of the elements were analyzed. The MD results are in reasonable agreement with the results obtained by DFT method. Our calculated results indicate that at room temperature, D2 molecule has higher affinity for U-G system than the H2 molecule. In order to increase the D2 separation factor from H2, the effect of temperature was studied. The results indicated that adsorption ratio of D2 to H2 increases by decreasing the temperature.

Density functional investigation of Kondo behavior, electronic structure and magnetic properties of CeRuPO-nano-layer

In this study, Kondo behavior, electronic structure and magnetic properties of CeRuPO-nano-layer are investigated using the first principles calculations. The calculations are performed by employing the full potential linearized augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). These properties are calculated in the presence of spin-orbit interaction. The exchange-correlation interaction is calculated within generalized gradient approximation (GGA). In addition, the GGA+U approach (where U is the Hubbard correlation term) is also employed to improve treatment of the f-electrons. The calculated partial electron density of states demonstrates that the hybridization between Ce-4f and Ru-5d orbitals and consequently Kondo effect changes at the surface of the CeRuPO-nano-layer compared to the bulk. The results show that due to the weaker Kondo effect at the surface of CeRuPO-nano-layer, the magnetic moment of Ce atoms enhances and the effective mass of the conduction electron reduces.

Impact of amphiphilic molecules on the structure and stability of homogeneous sphingomyelin bilayer: Insights from atomistic simulations.

Modulation of lipid membrane properties due to the permeation of amphiphiles is an important biological process pertaining to many applications in the field of pharmaceutics, toxicology, and biotechnology. Sphingolipids are both structural and functional lipids that constitute an important component of mechanically stable and chemically resistant outer leaflets of plasma membranes. Here, we present an atomistic molecular dynamics simulation study to appreciate the concentration-dependent effects of small amphiphilic molecules, such as ethanol, acetone, and dimethyl sulfoxide (DMSO), on the structure and stability of a fully hydrated homogeneous N-palmitoyl-sphingomyelin (PSM) bilayer. The study reveals an increase in the lateral expansion of the bilayer along with disordering of the hydrophobic lipid tails on increasing the concentration of ethanol. At higher concentrations of ethanol, rupturing of the bilayer is quite evident through the analysis of partial electron density profiles and lipid tail order parameters. For ethanol containing systems, permeation of water molecules in the hydrophobic part of the bilayer is allowed through local defects made due to the entry of ethanol molecules via ethanol-ethanol and ethanol-PSM hydrogen bonds. Moreover, the extent of PSM-PSM hydrogen bonding decreases with increasing ethanol concentration. On the other hand, acetone and DMSO exhibit minimal effects on the stability of the PSM bilayer at their lower concentrations, but at higher concentrations they tend to enhance the stability of the bilayer. The simulated potential of mean force (PMF) profiles for the translocation of the three solutes studied reveal that the free-energy of transfer of an ethanol molecule across the PSM lipid head region is lower than that for acetone and DMSO molecules. However, highest free-energy rise in the core hydrophobic part of the bilayer is observed for the DMSO molecule, whereas the ethanol and acetone PMF profiles show a lower barrier in the hydrophobic region of the bilayer.

Adsorption sensitivity of defected graphene towards NO molecule: a DFT study

Based on density functional theory, we studied the adsorption of a nitrogen monoxide (NO) molecule on the surface of perfect graphene (PG) and vacancy-defected graphene (VG), with the aim of searching the potential of graphene as an NO gas sensor. Different possible configurations have been considered for adsorption on vacancy-defected graphene split. The results indicated that the adsorption of the NO molecule on VG exhibited larger adsorption energy, higher charge transfer, smaller band length than that of perfect graphene. Meanwhile, the VG structure transformed a semiconductor into a conductor by the adsorption of the NO molecule. Furthermore, the partial electronic density of states (PDOS) results showed that hybridizations between the NO molecule and VG were mainly contributed by N-2p, O-2p, and C-2p orbitals. These results could provide useful information for the design of gas sensors based on graphene.

Exploration of selected electronic characteristics of half-sandwich organoruthenium(II) β-diketonate complexes.

Based on experimental work, 12 half-sandwich organoruthenium(II) complexes with p-cymene and various substituted β-diketonates (acac) modified by several functional groups were explored. These complexes were optimized at the B3PW91/6-31 + G(d)/PCM/UFF computational level with the Ru atom described by Stuttgart pseudopotentials. The electron density analysis was performed using the B3LYP/ 6-311++G(2df,2pd)/DPCM/scaled-UAKS model. Electrostatic and averaged local ionization potential were explored and extremes on 0.001 e/a.u.3 isodensity surfaces discussed. Natural population analysis partial charges and electron densities in bond critical point of the key Ru(II) coordination bonds were determined. There was a clear correlation between the results obtained and experimentally known anticancer descriptors. Graphical abstract Top Average local ionization potential (ALIP) of half-sandwich organoruthenium(II) β-diketonate complex, bottom IC 50 of b-series for ovarian cancer and Ru-P distances (in Å).

The structural, electronic and optical properties of Au–ZnO interface structure from the first-principles calculation

The interface structure, electronic and optical properties of Au–ZnO are studied using the first-principles calculation based on density functional theory (DFT). Given the interfacial distance, bonding configurations and terminated surface, we built the optimal interface structure and calculated the electronic and optical properties of the interface. The total density of states, partial electronic density of states, electric charge density and atomic populations (Mulliken) are also displayed. The results show that the electrons converge at O atoms at the interface, leading to a stronger binding of interfaces and thereby affecting the optical properties of interface structures. In addition, we present the binding energies of different interface structures. When the interface structure of Au–ZnO gets changed, furthermore, varying optical properties are exhibited.

Zinc Adsorption and Hydration Structures at Yttria-Stabilized Zirconia Surfaces

Zinc adsorption and interfacial hydration on yttria-stabilized zirconia (YSZ) surfaces in contact with aqueous zinc solutions at room temperature and neutral pH have been probed with combined specular high-resolution X-ray reflectivity and element-specific (Zn) resonant anomalous X-ray reflectivity techniques. The total and partial zinc-specific electron density profiles in the surface normal direction show the detailed interfacial hydration structures with zinc adsorption. Strongly depending on its crystallographic orientations, the YSZ (110) surface adsorbs zinc species only within adsorbed water layers above the terminal plane, while on (111) surface, zinc further penetrates the substrate (below the terminal plane). Considering that both surfaces are enriched with oxygen vacancies and metal-depleted sites, on which chemisorbed water species are expected, the observed contrast indicates that specific zinc adsorption is controlled strongly by the intrinsic surface chemistry that results from orientation-...

Core-hole Effect on Partial Electronic Density of State and O K-edge x-ray Raman Scattering Spectra of High-Pressure SiO2 Phases

Core-hole Effect on Partial Electronic Density of State and O K-edge x-ray Raman Scattering Spectra of High-Pressure SiO2 Phases

ELECTRONIC STRUCTURE OF DIVALENT METAL AZIDES

Ion-molecular metal azides are well known because of their high reactivity, and nowadays they are widely used as energetic materials. Despite the large amount of experimental data exists on such kind compounds, the number of theoretical studies is still not so large. The aim of the present work is to study of the electronic structure of Me(N3)2 compounds, where Me=Sr, Ca, Cd, Hg. All the calculations have been carried out within the framework of the density functional theory with the use of the numerical pseudo-atomic orbitals basis. The results of the band structure calculations are presented in the work together with a maps of total and partial electronic density; the data on Cd(N3)2 and α-Hg(N3)2 are presented for the rst time. The values of band gaps calculated are in good agreement with those obtained by other authors or estimated in the experiments. The all the crystals under consideration, except of α-Hg(N3)2, are predominantly ionic compounds with a relatively small fraction of the covalent bonding. The overall structure of the valence band spectra, as well as the character of conduction band bottom, is similar to other heavy metal azides. The comparative analysis of the data on band gaps led to the conclusion about lesser stability of the heavy metal azides than that of the second group metal azides, what is also conrmed by the experimental data

Indirect phase transition of refractory nitrides compounds of: TiN, ZrN and HfN crystal structures

The static and dynamical phase stabilities of refractory nitrides based on plane wave calculation in the framework of generalised gradient approximation (GGA) are reported in this work. The calculation reveals that the postulated zinc blende (B3) phase is statically and dynamically stable unlike the cesium chloride (B2) because of an appearance of imaginary modes in the phonon spectra which prevents the formation of this crystal phase similar to the corresponding carbides. The soft modes of the phonon bands were explored over a temperature range of 280–350K. The indirect phase transition pressures from the zinc blende to the cesium chloride structure are about 10-, 8-, and 7-fold lower compared with the direct transformation from the ground state rock-salt structure to the B2 phase of TiN, ZrN and HfN respectively. The calculated electronic partial density of states show strong hybridization at the gap region and that all the crystal phases are metallic. Again, the phonon calculation showed an appearance of phonon gap for the rock salt and the zinc blende phases but collapsed in the B2.

Theoretical prediction of a graphene-like structure of indium nitride: A promising excellent material for optoelectronics

Indium nitride is a very important solid state light material. Here we theoretically predict a planar graphene-like structure namely g-InN monolayer. We investigate its the mechanical, dynamical and thermal stabilities and structural, electronic, thermal, and mechanical properties via first-principles calculations. The electronic band structure shows that the g-InN monolayer possesses a direct band gap of 0.57eV. The analysis of its partial electron density of state reveals that the Nitrogen 2pz electrons and Indium 5s electrons are critical in forming this electronic band gap. The phonon band structure indicates that the plane structure is dynamically stable. Ab initio molecular dynamics simulations imply its thermal stability up to 600K. We obtained the Helmholtz free energy, entropy, and heat capacity at constant volume of g-InN monolayers as a function of temperature up to 600K. The Debye temperature is 290.92K. The g-InN has a low in-plane stiffness, and a high Poisson ratio of 0.586. The potential profiles and the stress–strain curves indicate that the free standing g-InN monolayers can sustain large tensile strains, up to 0.13, 0.21, and 0.15 for armchair, zigzag, and biaxial deformations, respectively. Our results imply that g-InN monolayers are excellent optoelectronics materials and mechanically, dynamically, and thermodynamically stable, suggesting that it is promising to fabricate it in near future. Our predicted elastic limits could provide a safe-guide for strain-engineering the g-InN based electronic devices.

Molecular and electronic structure of hydrolized platinum anticancer drugs as revealed by X-ray absorption, IR, UV-Vis spectroscopies and DFT calculations

The present study deals with the electronic structure of the bioactive anticancer drugs based on platinum(II) complexes: cisplatin PtCl2(NH3)2, carboplatin PtC6H12N2O4 and oxaliplatin PtC8H14N2O4, which are being used in cancer treatment. The purpose of the work was to examine the molecular and electronic structure of platinum(II) coordination complexes when they undergo hydrolysis, which is crucial in order to better understand their antitumor properties. The density functional theory (DFT) was used to investigate the electronic structure of the platinum(II) complexes under study. The process of hydrolysis was simulated, and the structure and geometry of hydrolyzed platinum complexes were determined. The electronic structure, energy levels of occupied and unoccupied MOs and the distribution of the total and partial electron density of states (DOS) were shown and the UV-Vis and oscillation spectra of the hydrolyzed platinum(II) complexes were calculated. The theoretical calculations were verified by the experimentally obtained data by applying the method of X-ray absorption at PtL3 edge as well as UV-Vis and IR spectroscopic techniques.

The effect of Ce dilution on the ferromagnetic ordering and Kondo behavior of CeRuPO

The structural, electronic and magnetic properties and Kondo behavior of Ce1−xLaxRuPO(x=0, 0.25, 0.5, 0.75 and 1) alloys are investigated using density functional theory by utilizing Wien2k package. The exchange-correlation potential is treated with the generalized gradient approximation (GGA). Moreover, the GGA+U approach (where U is the Hubbard correlation term) is employed to treat the f-electrons properly. We also present a comparative study between the electronic structure and magnetic properties of these alloys within GGA and GGA+U approaches. The calculated lattice parameters and bulk moduli of these alloys as a function of x are in the best agreement with Vegard's linear rule. The total and partial electron density of states and linear coefficient of electronic specific heat of these alloy within GGA and GGA+U are investigated and compared. The effect of La substitution on the Kondo behavior of CeRuPO compound is investigated.

Density functional study of O2 molecule and O atom adsorption on α-U(0 0 1) surface

First-principle calculations have been performed to study both O2 molecule and O atom adsorption on α-U(001) surface and subsurface. The results show that the long-bridge site is the most stable adsorption site for O2U(001) and OU(001) surface adsorption. The tetrahedral (Tet) 1 site is the most stable adsorption site for OU(001) subsurface adsorption. The partial electronic density of states (PDOSs) of O2U(001) and OU(001) shows the hybridization of U and O atoms orbitals causes the electrons of 5f/6d of U more non-local and leads to the formation of OU bond. The OU bond is partly ionic and partly covalent. The analysis of the diffusion path of O atom on U(001) shows that O atom can easily transfer from hollow (hol) 1 site to hollow 2 site with no energy barrier. O atom can hardly transfer from surface to the subsurface.

Vanadium Pentoxide Nanobelt-Reduced Graphene Oxide Nanosheet Composites as High-Performance Pseudocapacitive Electrodes: ac Impedance Spectroscopy Data Modeling and Theoretical Calculations.

Graphene nanosheets and graphene nanoribbons, G combined with vanadium pentoxide (VO) nanobelts (VNBs) and VNBs forming GVNB composites with varying compositions were synthesized via a one-step low temperature facile hydrothermal decomposition method as high-performance electrochemical pseudocapacitive electrodes. VNBs from vanadium pentoxides (VO) are formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT), assisting in enhancing the electronic conductivity coupled with the mechanical robustness of VNBs. From electron microscopy, surface sensitive spectroscopy and other complementary structural characterization, hydrothermally-produced rGO nanosheets/nanoribbons are decorated with and inserted within the VNBs’ layered crystal structure, which further confirmed the enhanced electronic conductivity of VNBs. Following the electrochemical properties of GVNBs being investigated, the specific capacitance Csp is determined from cyclic voltammetry (CV) with a varying scan rate and galvanostatic charging-discharging (V–t) profiles with varying current density. The rGO-rich composite V1G3 (i.e., VO/GO = 1:3) showed superior specific capacitance followed by VO-rich composite V3G1 (VO/GO = 3:1), as compared to V1G1 (VO/GO = 1:1) composite, besides the constituents, i.e., rGO, rGOHT and VNBs. Composites V1G3 and V3G1 also showed excellent cyclic stability and a capacitance retention of >80% after 500 cycles at the highest specific current density. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters, including charge transfer and solution resistance, double layer and low frequency capacitance, Warburg impedance and the constant phase element. The detailed analyses provided greater insights into physical-chemical processes occurring at the electrode-electrolyte interface and highlighted the comparative performance of thin heterogeneous composite electrodes. We attribute the superior performance to the open graphene topological network being beneficial to available ion diffusion sites and the faster transport kinetics having a larger accessible geometric surface area and synergistic integration with optimal nanostructured VO loading. Computational simulations via periodic density functional theory (DFT) with and without V2O5 adatoms on graphene sheets are also performed. These calculations determine the total and partial electronic density of state (DOS) in the vicinity of the Fermi level (i.e., higher electroactive sites), in turn complementing the experimental results toward surface/interfacial charge transfer on heterogeneous electrodes.

Phase equilibria in the U-Si system from first-principles calculations

Density functional theory calculations have been used with spin-orbit coupling and on-site Coulomb correction (GGA + U) methods to investigate the U-Si system. Structural prediction methods were employed to identify alternate stable structures. Convex hulls of the U-Si system were constructed for each of the methods to highlight the competing energetics of various phases. For GGA calculations, new structures are predicted to be dynamically stable, but these have not been experimentally observed. When the GGA + U (Ueff > 1.3 eV) method is considered, the experimentally observed structures are predicted to be energetically preferred. Phonon calculations were used to investigate the energy predictions and showed that the use of the GGA + U method removes the significant imaginary frequencies observed for U3Si2 when the correction is not considered. Total and partial electron density of states calculations were also performed to understand the role of GGA + U methods and orbitals on the bonding and stability of U-Si compounds.

Effect of Fe, Co, Si and Ge impurities on optical properties of graphene sheet

The electronic and linear optical properties of pure graphene and impurity-graphene (with Fe, Co, Si and Ge impurities) sheets are investigated by using the full potential linear augmented plane wave plus local orbital (FPLAPW+lo) in the framework of the density functional theory (DFT). The calculated results are obtained within the generalized gradient approximation using the Perdew–Burke–Ernzerhof scheme in the presence of spin-orbit interaction. The band structure, partial electron density of states, dielectric function, absorption coefficient, optical conductivity, extinction index, energy loss function, reflectivity and the refraction index of these sheets for parallel and perpendicular electromagnetic wave polarization to sheet are investigated. The optical conductivity of Si-graphene and Ge-graphene sheets for the parallel electromagnetic wave polarization to the sheet starts with a gap about 0.4eV confirms that these sheets have semiconductor behavior. Also the optical spectra of these sheets are anisotropic along these two wave polarizations. The dielectric function in the static limit of pure graphene sheet for perpendicular electromagnetic wave polarization to sheet does not significant change in the presence of Si, Ge, Fe and Co impurities. The static refractive index of Fe-graphene and Co-graphene sheets for parallel electromagnetic wave polarization to sheet is much larger than the corresponding value of pure graphene sheet.